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THE 
 
 WONDERS OE SCIENCE. 
 

Digitized by the Internet Archive 
 in 2016 
 
 https://archive.org/details/wondersofscienceOOmayh 
 
HUMPHRY AND HIS 
 
THE 
 
 WONDERS OF SCIENCE; 
 
 OR, 
 
 YOUNG HUMPHRY DAYY 
 
 (THE CORNISH APOTHECARY’S BOY, WHO TAUGHT HIMSELF NATURAL PHILOSOPHY, 
 AND EVENTUALLY BECAME PRESIDENT OF THE ROYAL SOCIETY). 
 
 Ik fife fff a ©Dnkrf«I §031 
 
 WRITTEN FOR ROYS. 
 
 BY 
 
 HENRY MAYHEW, 
 
 AUTHOR OF “THE STORY OF THE PEASANT-BOY PHILOSOPHER;” “LONDON LABOUR 
 AND THE LONDON POOR,” etc. 
 
 “Majestic steep ! ah, yet I love. 
 
 With many a lingering step to rove, 
 
 Thy ivied rocks among; 
 
 Thy ivied, wave-heat rocks recall 
 The former pleasures of my soul, 
 
 When life was gay and young. 
 
 Davy’s Ode to St. Michael’ 
 
 Enthusiasm— Nature’s child — 
 
 Here sung to me her wood-songs wild, 
 All warm with native fire 
 I felt her soul-awakening flame. 
 
 It made my bosom burn for fame, 
 
 It bade me strike the lyre.” 
 
 Mount in Cornwall . Written at the age of 18 . 
 
 WITH ILLUSTRATIONS RY JOHN GILRFRT. 
 
 fiction. 
 
 LONDON: 
 
 W. KENT & Co. (Late D. BOGLE), 86, FLEET STREET. 
 
 MDCCCLVIII. 
 
THOMAS HAERILD 
 
 LONDON: 
 
 cy% 
 
 SALISBURY SQUARE, 
 
 FLEET STREET. 
 
A WORD OR TWO 
 
 BY WAY OF 
 
 EXPLANATION AND DEDICATION 
 
 TO 
 
 MICHAEL FARADAY. 
 
 My dear Sir, 
 
 I inscribe your name on one of the 
 fly-leaves of this little book, with the same 
 devotion as youths are wont to carve upon the 
 trunk of some forest tree the name of those 
 whom they admire most in the world; and I 
 do so for many reasons. 
 
 First of all, because Davy was, as it were, 
 the foster-father of your great genius ; and, 
 secondly, because it allows me to tell the lads 
 for whom this book has been written the graceful 
 story of the way in which the hero of it first 
 befriended you — the young “ bookseller’s ap- 
 prentice, very fond of experiment, and very 
 averse to trade” — in your own dignified lan- 
 
yin 
 
 PREFACE. 
 
 guage; and, moreover, because I know your 
 zeal in the cause of education, and that you are, 
 like all generous minds when fired with the 
 beauty of fine truths and discoveries, unable to 
 rest, as it were, till you have imparted them to 
 others, and so made them as happy as yourself 
 with the wondrous knowledge. Indeed, it is 
 the glorious privilege of intellectual pursuits 
 that they are not marked by that selfishness,” 
 which made you as a boy desirous of escaping 
 from trade;” for wisdom, happily, can share 
 its riches with the world, and yet be all the 
 richer for the sharing. None know better than 
 yourself that every science is built up of an 
 infinity of such contributions ; and that, had the 
 human mind been impressed with a desire to 
 hoard its intellectual gains — to keep them 
 locked in the coffers of the brain — how little 
 even you — who have added, by your many pro- 
 found discoveries, more to the knowledge-fund 
 of the world than any other single philosopher — 
 could yourself have known. There is no finer 
 instance, perhaps, of human magnanimity than 
 the chemist working unseen in his laboratory — 
 watching alone for hours the action of different 
 kinds of so-called dead matter upon each other, 
 in the hope of being able to add his little mite 
 
PREFACE. 
 
 IX 
 
 of truth to that store of mental riches, which is 
 to benefit not only his own generation, but all 
 those to come for ages after. Nor can we de- 
 tract from the natural greatness of the act by 
 ascribing it to any lower principle of our soul — 
 such as that petty craving for praise which we 
 call “ vanity” in women, and a desire for fame 
 among poets and philosophers ; for every true 
 scientific mind knows that there is sufficient 
 reward in the intense beauty of a new discovery 
 — the first flash across the brain of some deep 
 insight into the mysteries of Nature — to repay 
 him, over and over again, for all the long puzzling 
 of his thoughts ; and that, were he even alone in 
 the world, without a voice to cheer him on, he 
 must still continue spelling out passage after 
 passage of the Great Poem of Creation, from 
 the mere love of the Poem itself. 
 
 I can readily understand that it was some such 
 generous purpose that first rendered you anxious 
 “ to enter the service of science, which,” as you 
 say, you “ imagined made its pursuers amiable 
 and liberal,” for this is impressed in every line 
 of the following letter, which becomes peculiarly 
 interesting as a record of the circumstances 
 which brought together two of the greatest 
 chemical geniuses that the world has yet seen. 
 
X 
 
 PREFACE. 
 
 “ To J. A. Paris, M.D. 
 
 “ Royal Institution , , Bee. 23, 1829. 
 
 “ My dear Sir, — You asked me to give you 
 an account of my first introduction to Sir H. 
 Davy, which I am very happy to do, as I think 
 the circumstance will bear testimony to his 
 goodness of heart. 
 
 “ When I was a bookseller’s apprentice, I was 
 very fond of experiment, and very averse to 
 trade. It happened that a gentleman, a member 
 of the Royal Institution, took me to hear some 
 of Sir H. Davy’s last lectures in Albemarle 
 Street. I took notes, and afterwards wrote them 
 out more fairly in a quarto volume. 
 
 “ My desire to escape from trade, which I 
 thought vicious and selfish, and to enter into the 
 service of Science, which I imagined made its 
 pursuers amiable and liberal, induced me at last 
 to take the bold and simple step of writing to 
 Sir II. Davy, expressing my wishes, and a hope 
 that, if an opportunity came in his way, he 
 would favour my views; at the same time, I 
 sent the notes I had taken at his lectures. 
 
 “ The answer, which makes all the point of 
 my communication, I send you in the original, 
 requesting you to take great care of it, and to 
 
PREFACE. 
 
 XI 
 
 let me have it back, for you may imagine how 
 much I value it. 
 
 “ You will observe that this took place at the 
 end of the year 1812, and early in 1813 he 
 requested to see me, and told me of the situation 
 of Assistant in the Laboratory of the Royal Insti- 
 tution, then just vacant. 
 
 “At the same time that he thus gratified my de- 
 sires as to scientific employment, he still advised 
 me not to give up the prospects I had before me, 
 telling me that Science was a harsh mistress; 
 and, in a pecuniary point of view, but poorly 
 rewarding those who devoted themselves to her 
 service. He smiled at my notion of the superior 
 moral feelings of philosophic men, and said he 
 would leave me to the experience of a few years 
 to set me right on the matter. 
 
 “ Finally, through his good efforts, I went to 
 the Royal Institution early in March of 1813, as 
 Assistant in the Laboratory ; and in October of 
 the same year went with him abroad, as his 
 assistant in experiments and in writing. I re- 
 turned with him in April 1815, resumed my 
 station in the Royal Institution, and have, as 
 you know, ever since remained there. 
 
 “ I am, dear Sir, very truly yours, 
 
 “ M. FARADAY.” 
 
ni 
 
 PREFACE. 
 
 The following is the note of Sir H. Davy, 
 alluded to in Mr. Faraday’s letter : — 
 
 To Mr. Faraday. 
 
 “December 24, 1812. 
 
 “ Sir* — I am far from displeased with the 
 proof you have given me of your confidence, 
 and which displays great zeal, power of memory, 
 and attention. I am obliged to go out of town, 
 and shall not be settled in town till the end of 
 January: I will then see you at any time you 
 wish, 
 
 “ It would gratify me to be of any service to 
 you. I wish it may be in my power. 
 
 “ I am, Sir, 
 
 “ Your obedient, humble servant, 
 
 i “ H. DAVY.” * 
 
 And now let me add, by way of excuse for 
 the many short-comings of the present volume, 
 that I have found some little difficulty in develop- 
 ing my object, which was to show youths how 
 one of the greatest natural philosophers had, 
 when a lad, like themselves, made himself ac- 
 quainted with the principles of science, and thus 
 
 * Extracted from Dr. Paris’s “ Life of Davy.” 
 
PREFACE. 
 
 Xlll 
 
 to induce them to “go and do likewise;” for, 
 assuredly, there is no education like that self- 
 education w^hich is sure to follow directly a fer- 
 vent taste is created for any particular branch of 
 knowledge. To create such a taste was my sole 
 motive for writing this book. Nevertheless, 
 when I came to deal with the subject, I dis- 
 covered that it was impossible to follow literally 
 the scientific history of Davy’s mind, since he 
 had begun by adopting the most flighty theories. 
 To have evolved all his visionary notions wdien 
 a lad, in a work that was meant to have an 
 educational tendency, would have been merely to 
 have taught error. I have, however, in adapt- 
 ing the book to the present state of science, de- 
 viated as little as possible from the biographical 
 facts, and I have, moreover, in all things striven 
 to be true to the character of my hero, which 
 after all is the great truth required in “story- 
 books.” Again, by a pardonable license, I believe 
 I have made the boy foreshadow some of his 
 after-discoveries — such as the safety-lamp — 
 and for all these deviations I can only plead a 
 desire to show youths that they have it in their 
 own powder to do as the Cornish apothecary’s boy 
 did, if they will but set about the work quickened 
 with the same determination to succeed. It is 
 
XIV 
 
 PREFACE. 
 
 my belief that our present system of education 
 begets in the minds of youths too great a sense 
 of dependence, and too little reliance on their 
 own powders, so that it is thought by a lad on 
 leaving school to be impossible to learn anything 
 without the help of a master to teach it. Now 
 my object in such books as the present is to 
 show boys that some of the greatest minds the 
 world has yet seen have been self-taught; and 
 by letting the young note how the great men, 
 when they were young too, set about the task of 
 informing themselves, thus to breed in youthful 
 minds not only a faith in their own capabilities, 
 but a taste for the beauties of knowledge, as well 
 as a strong purpose to number themselves, if pos- 
 sible, among the future teachers of mankind. 
 
 And now, my dear Sir, let me, in conclusion, 
 thank you for your generous encouragement of 
 my labours when I was engaged in inquiring 
 into the condition of the “ London Poor? Many 
 know your wisdom, but none are better ac- 
 quainted with your goodness than 
 
 Yours, very truly, 
 
 HENRY MAYHEW. 
 
 Bonn , Nov. 25th, 1854. 
 
CONTENTS. 
 
 CHAP. PAGE 
 
 I. THE WIDOWED AND THE FATHERLESS . 1 
 
 II. young Humphry's resolves . . id 
 
 III. HUMPHRY AND HIS MOTHER . . 34 
 
 IV. THE FIRST DRINK AT THE WELL . . 54 
 
 V. THE FIRST GLIMMER OF THE SAFETY- 
 
 LAMP .... 75 
 
 VI. THE WONDERS OF HEAT: ITS SOURCES . 94 
 
 VII. THE WONDERFUL DIFFUSION OF HEAT . 116 
 
 VIII., THE WONDERFUL EFFECTS OF HEAT . 173 
 
 IX. THE WONDERFUL EFFECTS OF HEAT 
 
 ( continued ) ..... 188 
 
 X. THE WONDERFUL EFFECTS OF HEAT 
 
 ( concluded ) . . ^ . 221 
 
 XI. HUMPHRY AND HIS “ WONDERFUL LAMP ” 265 
 
Xvi CONTENTS. 
 
 CHAP, PAGE 
 
 XII. HUMPHRY PRACTISES as A SURGEON 
 
 ON HIMSELF 293 
 
 XIII. THE FIRST SUN-PICTURES . .303 
 
 XI Y. THE WONDERS OF THE REFRACTJON OF 
 
 LIGHT ' . . .315 
 
 XV. THE WONDERS OF THE REFRACTION OF 
 
 light — ( continued ) . . .341 
 
 XYI. THE WONDERS OF THE REFLEXION OF 
 
 LIGHT . . . . 377 
 
 XVII. THE WONDERS OF COLOUR AND PHO- 
 TOGRAPHY . . . , .391 
 
 XVIII. CONCLUSION . 417 
 
THE WONDERS OF SCIENCE. 
 
 CHAPTER I. 
 
 THE WIDOWED AND THE FATHERLESS. 
 
 “ Well, gentlemen, I have gone over your several 
 accounts, and find that the debts of the late Mr. 
 Robert Davy amount altogether to the sum of 
 1 300 /.” 
 
 These words were addressed to a little group of 
 tradesmen and others who were assembled in a 
 small room over a mercer’s shop, in the town of 
 Penzance. There was Jan Penberthy, the neigh- 
 bouring miller, who, though in his holiday clothes, 
 had sufficient of the flour clinging io his black eye- 
 brows and whiskers to indicate his calling ; and 
 Malachy Carteret, the carpenter and builder, who 
 had slipped on his best coat, as he ran out from his 
 work, to be present at the meeting, and had still 
 the brass ends of his foot-rule projecting from the 
 little fob at the side of his fustian trousers. There 
 was Mr. Trevisky, too, the sporting lawyer, in his 
 check shooting -jacket, all over pockets, and those 
 at the hips large enough for game or law papers, 
 
 B 
 
2 
 
 THE WONDERS OF SCIENCE. 
 
 and who held in his hand a square, horny-looking 
 parchment deed ; and close beside him sat the 
 village apothecary, in a long, snuff-brown great- 
 coat, between the skirts of which might be seen, 
 shining in the light, his high boots, that reached 
 well up to his knees ; and there were two or three 
 other of the village tradespeople besides, all seated 
 at the end of the little apartment, and who, when 
 they heard the amount of their united claims, ex- 
 changed glances with one another in astonishment 
 at the largeness of the sum. 
 
 At a table in front of the little assembly sat 
 Mr. John Tonkin, the old gentleman who had 
 addressed them. Nor was he the least remarkable 
 among the company, for he was habited in the 
 costume that had been fashionable in the previous 
 century. Over his shrivelled and veiny hands 
 flapped deep lace-ruffles, and the top of his head 
 was white as a twelfth -cake, with the large 
 powdered wig that surmounted it. The straight, 
 stand-up collar of his Quaker-cut coat was as if 
 mildewed at the back with the powder that fell 
 from his peruke, and the large fan-like frill that 
 protruded from his waistcoat — which was long as 
 a modern groom’s — was speckled brown in places 
 with snuff, as thick as nutmeg on a custard ; while 
 from underneath the table at which he sat peeped a 
 pair of gold shoe-buckles and black silk stockings. 
 On a chair by his side lay the cocked hat which 
 
THE. WIDOWED AND THE FATHERLESS. 
 
 3 
 
 completed his antiquated costume, and the under- 
 neath part of which was greyed with hair-powder 
 and long usage. 
 
 Peculiar as was the old gentleman’s dress, yet it 
 had more of a quaint than comical appearance with 
 him ; for his features, though creased with age, 
 and his form, though slightly bowed with his load 
 of years, 'were still of too manly a cast to excite 
 any irreverent feeling, even in the lightest minds ; 
 indeed, he had too stern and austere a look to dis- 
 pose any to smile at the oddity of his costume.* 
 
 * Mr. Tonkin (says Dr. John Davy, in his Memoirs of the 
 Life of his brother) “ will long be remembered in Penzance, 
 both for excellences and peculiarities. The latter marked him 
 as a person of the gone-by time, and attracted the notiee even of 
 the careless observer. He held in aversion modern changes of 
 fashion, and in his old age wore the dress of his youth — the 
 cocked hat, large powdered wig, hand-ruffles, upright collar ; in 
 brief, the professional dress of the beginning of the last century — 
 and his manly form and countenance suited well with this vener- 
 able costume.” Dr. Davy says, moreover, that Mr. Tonkin 
 “ held a distinguished place among his fellow-townsmen, being 
 looked up to for his sterling worth and strength of judgment, 
 and very dear to his friends for his benevolence, kindness, and 
 very generous and friendly disposition.” He was “ of a quick 
 temper,” he adds, “ but his anger was of short duration.” — See 
 Life of Sir Humphry Davy , vol. i. p. 109. 
 
 Sir Humphry himself, in his last letter to Mr. Tonkin, says, 
 “ If I was nearer I would endeavour to be useful to you. I 
 would endeavour to pay some of the debts of gratitude I owe to 
 you, my first protector and earliest friend. As it is, I must look 
 forward to a futurity that will enable me to do this ; but believe 
 me, wherever I am, and whatever may be my situation, I shall 
 never lose the remembrance of obligations conferred on me, or 
 the sense of gratitude which ought to accompany them.” 
 
4: 
 
 THE WONDERS OF SCIENCE. 
 
 After a short pause the old gentleman continued 
 his address to the company before him. “ Now to 
 meet this sum of 1300/. there is the property of the 
 farm at Varfell, which is valued at about 150/. 
 a-year, and upon which Mr. Trevisky’s client has 
 a mortgage to a small amount.* 
 
 At the mention of the name of the attorney, that 
 gentleman proceeded to open the square deed before 
 him, and to throw back the huge skins, that looked 
 like large sheets of bladder, as he glanced his eye 
 down them one after another. 
 
 “ This little property, gentlemen,’' proceeded 
 Mr. Tonkin, “ is all that the widow and her five- 
 children — the eldest of whom, you will permit me 
 to remind you, is but sixteen years of age — have to 
 subsist upon. Mrs. Davy, therefore, I think, has a 
 claim to some little indulgence and sympathy at 
 your hands. Some years must pass before her 
 children are old enough to obtain a maintenance 
 for themselves, and in the mean time they have to 
 be supported, educated, and apprenticed. How t 
 this is all to be done upon such slender means is a 
 matter that I need not tell you adds severely to the 
 widow’s distress ; for not only has she the grief to 
 bear on losing the partner with whom she had lived 
 
 * “ When Mrs. Davy became a widow, she was in her thirty - 
 fonrth year, with five children, all of whom were still to be edu- 
 cated, excepting Humphry her eldest son. Her income at this 
 time was about 150/. a-year, and it was encumbered with a debt 
 of 1300/.” — Dr. Davy's Life of Sir Humphry , vol. i. p. 7. 
 
THE WIDOWED AND THE FATHERLESS. 
 
 5 
 
 in happiness for nearly twenty years, but she has 
 the greater grief, if possible, of knowing that her 
 children are fatherless, and that she herself lacks 
 the means of providing for them in comfort. Her 
 sorrow, then, gentlemen, has a double sting. It 
 arises not only from regret for the past, but a dread 
 of the future. I am sure, therefore, she will, under 
 her great affliction, meet with every consideration 
 from you.” 
 
 At this point Mr. Malachy Carteret — a little 
 man, remarkable for the blackness and bushiness 
 of his eyebrows, which grew so close together as to 
 look like one long one, rather than a pair, and who, 
 from his being considered a “ good prayer -maker ” 
 at the chapel to which he belonged, was always glad 
 of an opportunity of displaying his oratorical powers 
 — ventured to observe, that he was sure all then 
 present felt for Mrs. Davy under her trials, but 
 they had most of them children of their own, and 
 it was their duty to look at home first ; for who 
 could tell how soon they themselves might be called 
 away, and their little ones left in the same distress- 
 ing situation, unless their bills were duly paid? 
 “ Now my little account,” proceeded the carpenter, 
 “ has been standing so long as the new house at 
 Yarfell has been built, and that were the same year 
 as Dolly Pentreath died — I mean her as were 102 
 year old — and that’s soma time agone, you know ; 
 so I’m sure no one can’t say as I’ve been hard about my 
 
6 
 
 THE WONDERS OF SCIENCE. 
 
 little matter. But we were a-thinkjng among our- 
 selves, Mr. Tonkin, that as you’d always been suchy 
 kind friend to the family, and as we hadn’t no wish 
 to trouble Mrs. Davy under her affliction, that 
 maybe a — a — you — you — you wudn’t mind be- 
 coming security yourself for the debts, and then 
 they cud stand over for another year or two if need 
 be. You’ll excuse ma making maself so bould, sir ; 
 but I’m a plain man, and think plain speaking is 
 better than double-dealing at ale times.” 
 
 The old gentleman’s brow fell suddenly, and 
 locking the carpenter full in the face, he said, 
 scornfully, — “ Though you have no wish to trouble 
 Mrs. Davy under her afflictions, you would not 
 object, it seems, to involve her friends in her lia- 
 bilities. You allude, sir, to my past services, and 
 surely the recollection of the melancholy occasion 
 which rendered such services necessary should 
 have made you less eager after what is due to you, 
 and less anxious to entangle in the family diffi- 
 culties a person who, when he found that his assist- 
 ance was needed, has never added to the distress by 
 waiting till asked for it. In this very house, now 
 thirty-seven years ago, it was my sad lot to see 
 three young girls deprived of both father and 
 mother in the same week. Mrs. Davy was one, and 
 the youngest of those three — left almost in her 
 infancy without a friend or counsellor to help her 
 through the world. And now in her womanhood 
 
THE WIDOWED AND THE FATHERLESS. 
 
 7 
 
 the same hard fate attends her — bereft of him whose 
 affection had made him her protector, and finding 
 her children fatherless, as she herself was, at the 
 very time when needing most a father’s care. 
 Surely the remembrance of a double bereavement 
 like this, sir — for hardly is she out of her orphan- 
 age before she is doomed to enter on her widow- 
 hood — should teach you that Providence must 
 have some special design in visiting so much misery 
 upon this poor lady.* Nevertheless, I am happy to 
 say that Mrs. Davy needs no pecuniary assistance 
 from her friends, and requires but little indulgence 
 from those to whom her husband was indebted. It 
 is proposed to increase the mortgage upon the farm 
 at Yarfell to the amount of 1300/., though this — 
 
 * “ Mrs. Davy was the third and youngest daughter of Grace 
 and Humphry Millett Mr. Millett was engaged in busi- 
 
 ness in the town of Penzance as a mercer. He and his wife died 
 young, and in the same week , — he on the 3d of June, 1757, and 
 
 she on the 9th Mr. John Tonkin was their friend, and 
 
 supplied the place of a father to them (the orphan children), and 
 they retained through life a most grateful sense of his kindness, 
 and of the great obligations they owed to him. At the time of 
 the death of Mr. and Mrs. Millett, he (Mr. Tonkin) was residing 
 in their house (I suppose in lodgings) , and there he continued to 
 reside for some years, the children being under the care of a 
 Miss Peggy Adams, their cousin, in whose name the mercer’s 
 business was continued, by the profits of which the family was 
 chiefly supported.” — Dr. John Davy , p. 7. vol. i. 
 
 Dr. Paris, in his life of Sir Humphry Davy (p. 2), says, speak- 
 ing of the philosopher’s mother, “ Her maiden name was Grace 
 Millett, and she was remarkable for the placidity of her temper 
 and the amiable and benevolent tendency of her disposition. She 
 
s 
 
 THE WONDERS OF SCIENCE. 
 
 even if Mr. Trevesky can obtain the money at 4 
 per cent — will reduce the family income to less 
 than 1 00/. a-year ; and immediately the mortgage 
 is completed and the money paid, your accounts, 
 gentlemen, will be discharged. The reason of my 
 requesting your attendance here to-day was not to 
 seek to make any compromise with you, nor to 
 crave any unusual indulgence at your hands, but. 
 merely to ascertain the amount of the collected 
 claims against the late Mr. Davy, and to inform 
 you that steps were being taken for a speedy pay- 
 ment of them, so that you might not trouble his 
 widow with any importunities on the matter. She, 
 poor soul, has enough to bear with in the privation 
 she has recently suffered, and those worldly ones 
 
 had been adopted and brought up with her two sisters, under 
 
 circumstances of affecting interest, by Mr. John Tonkin 
 
 To withhold a narrative of the circumstances which led Mr. 
 Tonkin to the adoption of these orphan children would be to 
 deprive the world of one of those bright examples of pure and 
 disinterested benevolence which cheer the heart and ornament our 
 
 nature The parents of these children having been 
 
 attacked by a fatal fever expired within a few hours of each 
 other. The dying agonies of the surviving mother were sharp- 
 ened by her reflecting on the forlorn condition ir» which her 
 children would be left. For, although the Milletts were originally 
 aristocratic and wealthy, the property had undergone so many 
 subdivisions as to have left but a very slender provision for the 
 member of the family to whom she had united herself.” On the 
 decease of Mrs. Millett (Dr. Paris tells us), Mr. Tonkin imme- 
 diately took charge of her three orphan daughters, and “ con- 
 tinued their kind benefactor until each in succession found a 
 home by marriage.’ ’ 
 
THE WIDOWED AND THE FATHERLESS. 
 
 9 
 
 which threaten herself and children in the future ; 
 but, thank Heaven, she is prepared to meet all her 
 trials with resignation and courage.” 
 
 Then, rising from his seat, he bowed haughtily 
 to the company as he said, “ Now, gentlemen, I 
 wish you a good day.” 
 
 The words were no sooner uttered than Mr. 
 Trevisky, who had previously folded up the deed, 
 and sat fidgetting on his chair for the last quarter 
 of an hour — now twisting a piece of red tape round 
 and round — then paring his nails — and then twid- 
 dling the brass fox’s-head buttons of his shooting- 
 jacket, — the words were no sooner uttered, we 
 repeat, than the lawyer started to his feet, and, 
 pulling out his watch, said, half to himself, 
 “ Egad, I shall be in time for the cock-fight yet ; ” 
 and then, waving his hand rapidly in the air, 
 shouted as he darted from the room, “ I’ll see to 
 that directly, Mr. Tonkin, — I’ll see to it directly.” 
 
 Malachy Carteret was the last to leave, for 
 he purposely remained behind to plead his excuse 
 to Mr. Tonkin for the use he had made of his 
 name. 
 
 “ I hope no offence, I’m sure, sir,” began the 
 little carpenter. “ I always thoft ma money safe 
 enow, but ya see times is hard, and there’s the men 
 to pay every Saturday night, and that’s a great 
 pull. No one feels more for Mrs. Davy than your 
 humble servant M. C. does. Her husband always 
 
10 
 
 THE WONDERS OF SCIENCE,. 
 
 behaved honourable to me, and M. C. is ‘ ever 
 grateful for past favours,’ as my card says. That 
 there wor a bit of poor Mr. Davy’s handiwork, 
 worn’t it, Mr. Tonkin ? ” added Malachy, pointing 
 to the oak mantel-piece, that was elaborately and 
 beautifully carved with birds, fruit, and flowers. 
 
 “ Yes,” returned the old gentleman, dryly : “ Mr. 
 Davy presented it to me when he used to come 
 courting here, at the time his wife and her sisters 
 were under my care.” 
 
 “ Ah, he wor very clever with his tools,” con- 
 tinued the carpenter. “ 4 The last of the carvers,’ 
 we used to call him. I remember him afore he 
 went to London to larn the business — he lived with 
 his uncle Robert then. I used to work for the uncle ; 
 indeed I sarved my time with the late Mr. Davy’s 
 father — the builder, ya know, — so, of coose, I 
 cudn’t mean anything but kindly to the family — 
 only money’s very scarce just now, sir, and IVe 
 a-mashes of bills to meet this quarter : so I hope no 
 offence, I hope no offence, sir. You doan’t want 
 nothing in my way, do you, Mr. Tonkin?” 
 
 The old gentleman shook his head. 
 
 “ Yery well, sir,” proceeded the tradesman ; 
 “ when you do, M. C. will be proud to take your 
 orders — ever grateful for past favours, sir, and 
 hoping for a continuance of your kind support. 
 Allow me to give you one of my new cards, sir ; 
 you’ll see I says as much there.” So saying, the 
 
THE WIDOWED AND THE FATHERLESS. 
 
 11 
 
 pushing little carpenter thrust one of the printed 
 bits of pasteboard into the old gentleman’s hand. 
 
 Suddenly a loud shout was heard in the street 
 beneath. 
 
 Malachy and Mr. Tonkin looked vacantly at one 
 another, as they both inwardly wondered as to the 
 cause of the noise. 
 
 In a few minutes the shouting was repeated, and 
 this time the ear, quickened by curiosity, could 
 distinguish the shrill cries of the village boys and 
 women among the rest. 
 
 The carpenter, in the excitement of the moment, 
 forgot his customary obsequiousness, and rushing 
 towards the window threw open the little diamond- 
 paned casement, making its metal frame twang 
 again as he did so ; and as he craned his neck over 
 into the street he cried, “ Oh, Mr. Tonkin, Mr. 
 Tonkin ! here, you never saw suchy thing in ale 
 your life !” 
 
 The old gentleman was sufficiently curious to be 
 unable to resist sharing in the excitement, and pro- 
 ceeded to join the little carpenter, who was still 
 eagerly surveying the mob that was gathered round 
 about the “ Star Inn,” on the opposite side of the 
 street. 
 
 “ It’s Squire Giddy’s new conveyance, sir !” ex- 
 claimed Malachy. “ The gardener told me last 
 night it had come down from London the day 
 afore, with all its wheels done up in haybands 
 
12 
 
 THE WONDERS OF SCIENCE. 
 
 like an Irish reaper’s legs. It’s the fust as has 
 ever bin seen in these parts, and so of coose the 
 whole town has come to have a peep at it.” 
 
 Ay, so it had ! All Penzance was out to behold 
 the first carriage that had ever appeared in its 
 streets. 
 
 There were the fishwomen from the neighbouring 
 villages of Mousehole and Newlyn, who had stopped 
 in their rounds to join in the throng, and who had 
 their “ eowals ” or panniers of fish slung round the 
 crown of their broad -brimmed hats, with the load 
 of pilchards glittering like lumps of silver at their 
 backs. And there were the ruddy-faced oil-girls, 
 who had put down their heavy pitchers and ceased 
 for a while their cries of “ Buy ma traa-in ! Buy 
 ma traa-in ! ” to eye “ the big box upon wheels,” 
 as they called it. The portly town-crier, too, was 
 there, with his huge dustman - like bell turned 
 upwards, and looking like a big tulip in his hand ; 
 for having found that his audience had suddenly 
 deserted him, and were more attracted by the sight 
 of the new conveyance than with his announce- 
 ment that the grocer “ had just received several 
 chests of the best tea from London,” the bellman 
 had himself helped to swell the crowd, and was 
 now as eager as any to obtain a view of the new 
 wonder. Mingling with these might be seen the 
 forms of the boatmen — half-smugglers, half-fisher- 
 men — from the neighbouring shore, with their tight- 
 
THE WIDOWED AND THE FATHERLESS. 
 
 13 
 
 fitting blue “ Guernseys,” their yellow, greasy -look- 
 ing, fan-tail hats, and their large high jack-boots, 
 that bagged about their legs and looked as rusty as 
 if they had been made out of brown paper ; whilst 
 at the outside of the motley group the eye fell upon 
 the news-boy, mounted on a podgy pony, with his 
 long tin horn in his hand and pad of “ Sherborne 
 Mercurys” under his arm ; and he, in his eagerness 
 to catch sight of the strange -looking vehicle, was 
 leaning over on one side of the saddle, as a butcher- 
 boy loves to ride. All the shop people were at their 
 doors : some in long aprons, and others with white 
 sleeves on their arms over their coats ; and the boys 
 kept darting across from the houses towards the 
 mob ; while the upper windows all down the street 
 were knobbed over with heads, each bent towards 
 the one grand focus of attraction. 
 
 « It’s a queer-looking consarn, aint it, sir?” in- 
 quired Malachy ; “ and there’s a good bit a work in 
 it, I’ve no doubt.” 
 
 “It’s a hideous lumbering affair,” responded the 
 old gentleman, as he turned away from the window, 
 “and it’s a great pity that persons haven’t some- 
 thing better to excite their admiration than the 
 follies of the rich ; but there’s such a love of luxury 
 coming over our people, that soon we shall become 
 as effeminate as those of the East, who are 
 borne about upon couches when they journey 
 from one place to another. In times past we were 
 
14 
 
 THE WONDERS OF SCIENCE. 
 
 a sturdy, energetic race, inured to hardship, and 
 loving, rather than avoiding, exercise ; but now we 
 must have soft, easy seats, and beds of down, or we 
 cannot rest. Not many years back the floors of 
 our nobles’ houses were strewn with rushes, but at 
 present even our gentry are beginning to find a 
 sanded room unpleasant to their feet, and so they 
 must needs have soft carpets to tread upon — as if 
 they had all at once grown as tender-footed as 
 negroes. There’s Squire Austell has already car- 
 petted his best sitting-room ; and mark my words ! 
 there ’s sufficient of the monkey in our natures to 
 make his great and little neighbours ape the Squire’s 
 manners. Ugh ! We shall be as unmanly as fid- 
 dlers before many years have passed over our heads. 
 Haven’t we got to drink slops for breakfast instead 
 of a horn or two of good strong ale, as they did in 
 our fathers’ time ? and do you think, sir, strength, 
 and courage, and energy are to be got out of tea-cups ? 
 Soon we shall find it impossible to eat without 
 silver forks, as they do in London already ; and, by 
 and by, the dinner-bell will ring at the same hour 
 as the curfew-bell used to toll in olden times — for 
 what’s called fashion is setting nearer that way 
 every day. But, thank goodness, we still dine 
 at noon here, and our parties are limited to tea 
 and Pope Joan at three o’clock, instead of grand 
 dinners or dances with Frenchified gavottes, and 
 minuets that begin with the owls and end with the 
 
THE WIDOWED AND THE FATHERLESS. 
 
 15 
 
 lark. I hate such new-fangled customs ! they 
 would put John Bull into stays like a Frenchman, 
 and exchange his top-boots for dancing pumps. 
 Take my word for it, sir, since that four-wheeled 
 aid-to-laziness has appeared in our town we shall 
 shortly find every one of our would-be fine ladies 
 unable to stir a yard from their homes without 
 one.”* 
 
 “You’re quite right, Mr. Tonkin, quite right, 
 sir,” chimed in the little carpenter ; “ our rich folk 
 
 * “ The state of society in the Mount’s Bay only half a century 
 ago,” says Dr. John Davy, “was peculiar and different from 
 what it is at present. Cornwall was then without great roads. 
 The roads which traversed the country were bridle-paths rather 
 than carriage roads. Carriages were almost unknown, and carts 
 even very little used. I have heard my mother relate that when 
 she was a girl there was only one cart in the town of Penzance, 
 and if a carriage appeared in the streets it attracted universal 
 attention. Pack-horses were then in general use for conveying 
 merchandise, and the prevailing manner of travelling was on 
 horseback. In the same town, where the population was about 
 2000 persons, there was only one carpet ; the floors of rooms w ere 
 sprinkled with sea sand, and there w r as not a silver fork. The 
 only newspaper which then circulated in the West of England 
 was the ‘ Sherborne Mercury,’ and it w T as carried through the 
 country, not by the post, but by a man on horseback, specially 
 employed in distributing it Visiting was then con- 
 
 ducted differently from what it is at present. Dinner-parties were 
 almost unknown, excepting at the annual feast time. Christmas, 
 too, was then a season of peculiar indulgence and conviviality, 
 and a round of entertainments were given, consisting of tea and 
 supper. Excepting at these two periods, visiting was almost 
 entirely confined to tea-parties, which assembled at three o’clock 
 and broke up at nine, and the amusement of the evening was 
 commonly some round game at cards, as Pope Joan or Com- 
 
16 
 
 THE WONDERS OF SCIENCE. 
 
 are getting more proud and fond of luxuries and 
 vanities every day of their lives. Why, what do you 
 think ? they’re talking of putting cushions to all the 
 seats of the pews in our chapel, sir, just because the 
 gentlefolks has ’em to their sittings in Madern church ! 
 and I give you my word, sir, I’ve only just finished 
 setting a bright polished steel grate in the withdraw- 
 ing -room, as they call it, at Castle Horneck. It’s 
 just bin had down from London, and I declare one 
 might see to shave one’s self in any part of it. It 
 
 merce Amongst the middle and higher classes 
 
 there was little taste for literature, still less for science, and their 
 pursuits were rarely of a dignified or intellectual kind. Hunt- 
 ing, shooting, wrestling, cock-fighting, generally ending in 
 drunkenness, were what they most delighted in. Smuggling 
 was carried on to a great extent, and drunkenness and a low 
 scale of morals were naturally associated with it. . . . Few 
 
 places have exhibited greater changes within the last half century 
 than Penzance. Not a single family belonging to the great 
 gentry now in existence west of Havle, or in the Mount’s Bay, 
 was known one hundred years ago.” 
 
 Carriages, it may be added, are of French invention. Under 
 Francis I. (a.d. 1515-1547), who was contemporary with our 
 Henry VIII., there were but two in Paris, one of which belonged 
 to the Queen, and the other to Diana, the natural daughter of the 
 French Henry II. There were but three in Paris in 1550; 
 Henry IV. of France (a.d. 1589-1610) had one, but of very rude 
 construction, and without straps or springs. The first courtier 
 who set up this equipage in France was John de Laval de Bois- 
 Dauphin, who could not travel otherwise on account of his enor- 
 mous bulk. Previously to the use of carriages the kings of France 
 travelled on horseback, the princesses were carried in litters, and 
 ladies rode behind their squires. The first carriage seen in Eng- 
 land was in the reign of Mary, about 1553 ; but the art of making 
 them was unknown in this country at that time. Close carriages 
 
THE WIDOWED AND THE FATHERLESS. 
 
 17 
 
 never was made to put a fire in, I’m sure. But 
 there ’s nothing I can do for you in my little way ; 
 is there, Mr. Tonkin ? I’ve got the newest designs 
 for furniture just arrived from town by the pack- 
 horse as came in last Monday.” 
 
 Mr. Tonkin shook his head, and turned towards 
 the window. 
 
 “ I hope no offence, sir,” continued Malachy ; 
 “ another time, maybe, I shall be honoured with 
 your commands, and then I can only say that your 
 
 of good workmanship began to be used by persons of the highest 
 quality at the close of the sixteenth century; Fitz-Allen earl of 
 Arundel is said to have been the first who used them, and this was 
 in 1580 ; their construction was various. They were first made in 
 England about the year 1590, when they were called ‘ whirlicotes.’ 
 In the year 1601, an Act was passed to prevent the effeminacy of 
 men riding in carriages (43d Elizabeth). The Duke of Bucking- 
 ham, in 1619, was the first who had a carriage with six horses 
 to it ; and the Duke of Northumberland, on obtaining his libera- 
 tion from the Tower (where he had been imprisoned since the 
 Gunpowder Plot) and hearing that Buckingham w T as drawn about 
 with six horses to his carriage, ordered, out of rivalry, eight 
 horses to be put to his, and in that manner passed from the 
 Tower through the City.” — Haydn's Dictionary . 
 
 “ In the twelfth century carpets wrere articles of luxury. It is 
 mentioned by old English historians, as an instance of Bechet’ s 
 splendid style of living, that his sumptuous apartments were, 
 every day in winter, strewn with clean straw or hay. This was 
 about the year 1160. The manufacture of woollen carpets w r as 
 introduced into France from Persia at the end of the sixteenth or 
 beginning of the seventeenth century. Some artisans, who had 
 quitted France in disgust, came over to England and established 
 the carpet manufacture among us about 1750. Our Kidder- 
 minster, Axminster, and Wilton manufactures are the growth of 
 the last hundred years.” — Ibid. 
 
 C 
 
18 
 
 THE WONDERS OF SCIENCE. 
 
 orders shall be punctually attended to by your 
 humble servant, M. C. and, having delivered 
 himself of this speech, the pushing little carpenter 
 bowed himself backwards out of the room. 
 
young Humphry’s resolves. 
 
 13 
 
 CHAPTER II. 
 
 young Humphry’s resolves. 
 
 “ The first and last Inn in England, kept 
 by Richard Botheras,” was the inscription re- 
 corded on both sides of a sign -board that swung 
 backwards and forwards outside a little lonely 
 homestead — more like a cottage than a tavern — 
 standing at the extreme western point of Cornwall. 
 
 The open door revealed a room without a visitor; 
 the floor was white with sea-sand, and you could 
 tell at a glance, from the evenness with which the 
 sand was strewn, how scanty were the customers in 
 that part of the world, for it was plain that no foot 
 had trodden it that day. Above the ample chimney- 
 board was ranged a row of bright tin mugs, that had 
 been worn more by polishing than use. The top 
 of the little round deal table that stood in the 
 centre of the room was as clean as if it had 
 been newdy planed ; and over the painted chest of 
 drawers, in one corner, stood what appeared like 
 a quire of tea-boards, which, together with the 
 written paper pasted against the wall, and in- 
 
20 
 
 THE WONDERS OF SCIENCE. 
 
 forming the stranger that “ parties were supplied 
 with hot water,” gave one a notion of the many 
 visitors who came in summer to take tea at the 
 Land’s End. 
 
 The host, from lack of custom, was busy in the 
 garden at the back, digging in refuse fish as ma- 
 nure for his next year’s crop ; and the hostess might 
 be seen in the adjoining out-house, with her arms 
 half buried in a cushion of dough, preparing the 
 week’s bread for the humble family. 
 
 Suddenly the innkeeper paused, with his foot 
 resting on his spade. His quick ear had caught 
 the clink of a horse’s hoofs on the neighbouring 
 granite. The man put his hand across his brows, 
 and looked under it in every direction to see who 
 was coming. 
 
 In a minute or two afterwards he ran to his 
 wife, crying, “ Come, tidy thaself a bit, dame ! — 
 Here’s Master Davy on his pony Derby jist at 
 hand : lie’s ale in deep black, too.” 
 
 The good wife was not long in scraping the 
 dough from her hands, and, having invested herself 
 in a clean apron, was quickly at the door beside 
 her husband, awaiting the arrival of the youthful 
 visitor. 
 
 As the innkeeper had stated, the lad was dressed 
 in deep mourning, and the beaver of his hat was 
 completely hidden by the broad crape band that - 
 encircled it, while the gloss upon his clothes indi- 
 

 
young Humphry’s resolves. 
 
 21 
 
 cated the recent loss he had met with. To a casual 
 observer there was but little in the youth’s ap- 
 pearance to mark the budding genius which in- 
 spired him, excepting the ample forehead and the 
 full black eyes beneath it. He was, however, 
 generally considered an “ extraordinary - looking 
 boy.” He was of diminutive stature, while the 
 roundness of his shoulders gave him somewhat — 
 as it has been termed — of a “ bucolic aspect.” 
 His hair was chestnut brown, and hung in neg- 
 lected curls about his brow ; his eyes were dark 
 and piercing, but the rest of his features were any- 
 thing but finely chiselled. His complexion ap- 
 peared paler than ordinary, from the contrast of 
 the suit of black in which he was habited, and 
 the dejected air and wet-looking eye gave a me- 
 lancholy tone to his appearance that immediately 
 enlisted the heart towards the boy.* 
 
 * “ Davy, it may be remarked, possessed, when a boy, a coun- 
 tenance which, in its natural state, was very far from comely ; 
 while his round shoulders, inharmonious voice, and insignificant 
 manner, were calculated to produce anything rather than a 
 favourable impression. In riper years he was what might be 
 called 1 good-looking ; ’ although, as a wit of the day ob- 
 served, his aspect certainly was of the * bucolic’ character.” — 
 Dr. Paris' Life of Sir Humphry Davy, p. 33. The Doctor after- 
 wards describes young Davy as an “ extraordinary-looking boy.” 
 “ His manners were retreating and modest,” says Mr. Poole 
 (one of Davy’s oldest friends), in a letter to Dr. Paris, speaking 
 of Sir Humphry in early life; “he was generally thought 
 naturally graceful, and the upper part of his face was beau- 
 tiful. When he first lectured at the Royal Institution, the 
 
22 
 
 THE WONDERS OF SCIENCE. 
 
 The lad said but a word or two in answer to 
 the greeting of the couple, and jumping from the 
 saddle, gave the reins to the innkeeper, who forth- 
 with led the plump little animal round to the 
 stable. 
 
 The instant after the youth had disappeared 
 among the rocks. 
 
 “ Poor lad ! he seems deeply cut up ; doan’t he, 
 Richard ? ” said the wife, following her husband to 
 the shed. 
 
 ladies said, 1 Those eyes were made for something besides poring 
 over crucibles.’ ” — Dr. John Davy's Life of his Brother , vol. i. 
 p. 136. “ I was very young,” Lady Brownrigg says, in a 
 
 letter to Dr. Davy, “ when I first had the pleasure of seeing 
 your highly-gifted brother. We had been invited by Dr. Richard- 
 son to go to his cottage at Portrush, to meet the famous 
 Mr. Davy. We arrived a short time before dinner ; in passing 
 through a room we saw a youth, as he appeared,” (Davy was 
 twenty-eight years of age at this time) “ who had come in from 
 fishing, and who, with a little note-book, was seated in a 
 window-seat, having left a bag, rod, &c. on the ground. He was 
 very intent on this little book, and we passed through unnoticed. 
 When I went into the drawing-room I felt some little awe at 
 this great philosopher, annexing to such a character, at least, 
 the idea of an elderly grave gentleman — not, perhaps, with so 
 large a wig as Dr. Parr, or so sententious a manner as Dr. 
 Johnson — but certainly I never calculated on being introduced 
 to the identical youth, with a little brown head like a boy, that 
 we had seen with his book at the window-seat, and who when I 
 came into the drawing-room was, in the most animated manner, 
 recounting an adventure which had entertained him on the 
 Causeway, and, from his mode of telling it, was causing loud 
 laughing in the whole room.” — Given in the Life of Sir Humphry , 
 by Dr. John Davy , who speaks of the above account as being 
 “ very descriptive of the appearance and manner” of his brother 
 at this time.” 
 
' young Humphry’s resolves. 23 
 
 “ Ah, that he doa,” returned Richard, as he 
 stooped down under the pony to loosen its girths. 
 “ He’s not tha maze-gerry hoy he was a little while 
 agone, when he used to come over here, Greace, 
 with a hammer a cracking all the stones that lay in 
 his way into ‘midjons and jouds,’ and scrambling, 
 like a young goat, over the rocks after some 
 trumpery bit of stone as took his fancy — -just as 
 our Jan do after daws’ eggs.” 
 
 “ Yes, that he used to,” returned the wife, 
 taking off her clean apron, and carefully folding 
 it up as she talked ; “ and I’ve seed Master Hum- 
 phry come back, after being out all day among 
 the rocks, with his cap full of old stones, as he 
 seemed to prize like as if they was lumps of goold, 
 but such as I wodn’t a picked out of ‘ a stomps ’ — 
 not I. Ah ! there’s sad trouble at Yarfell now, 
 take my word for it, Richard. Mistress Davy, 
 poor thing ! has seen enough sorrow in her time to 
 ha’ broke many a stout heart; and here she’s left 
 with five young ones, and not a ‘ cheeld-yean ’ among 
 ’em as can get a penny to help her. Master 
 Humphry ’s a good scholard, they say; but laming 
 won’t fill the cupboard, Dick ; and they tells me, 
 down at Penzance, that Mr. Davy (rest his soul !) 
 was too fond of wasting his money in mines — as 
 we’ve seen many a family ruined with in our day — 
 to leave his wife anything to fall back upon at 
 this time ; though I’m sure I pity the poor widow 
 
24 
 
 THE WONDERS OF SCIENCE. 
 
 and her little ones from the bottom of my heart, 
 for it isn’t none of their bringings on. Sometimes, 
 do you know, Dick, I fancy as there’s a spell on 
 that poor woman.” 
 
 “ Go along with you and your spells ! ” indig- 
 nantly shouted the husband, as he held the pail 
 of water for the pony to drink from ; “ you’ve 
 always got some stuff of that kind in your head, 
 Greace.” 
 
 “ Well, you may talk as you like, but I shall 
 b’lieve in such things to my dying day,” retorted 
 the superstitious little body. “ Didn’t I go to 
 Madern Well and drop some pins into it ; and 
 didn’t they fall with their pints together, I should 
 like to know ? And wasn’t our old sow took ill 
 the very week afterwards, and died on the very 
 day as we’d settled to kill her — eh ? Oh ! you’re 
 as unb’lieving as a Jew ; you are, indeed, Dick.” 
 
 The innkeeper treated his wife’s argument with 
 a hearty laugh, whereupon the dame proceeded to 
 cite to him a hundred and one such instances as 
 were current throughout the county, and in the 
 midst of which we must leave the worthy couple 
 for the present. 
 
 The restless, pensive boy, had wandered to the 
 extreme point of the land, and here, resting upon 
 a shelf of crag far above the sea, that roared and 
 dashed against the base, he sat for a while, with 
 
young Humphry’s resolves. 
 
 25 
 
 his tearful eye peering across the Atlantic, vacantly 
 gazing at the huge watery disc that heaved like a 
 giant breast before him. Behind the lad towered 
 tremendous pinnacles of granite, some with their 
 monster blocks, ranged in cubes one above the 
 other, like Nature’s solid masonry ; others with 
 massive stones standing right on end; while some 
 seemed tossed about in such confusion as if the 
 “sixth seal” itself had opened, and the heavens 
 had rained rocks upon the land. Here a large 
 square lump protruded like a bond-stone from the 
 straight sides of some tall pile ; there a huge mass 
 was scored through at the top, leaving the blocks 
 standing up on either side of it, as if castellated ; 
 and there again was seen a ponderous lump, so 
 delicately balanced on some high peak, that it 
 seemed as if the least gust would topple it over 
 into the sea beneath ; while the outline of the whole 
 was as jagged as if it had been gnawed, or as if 
 the entire granite pile were some immense crystal 
 that the sea was gradually dissolving away. Be- 
 low the height the crags stretched far out into 
 the sea, their black and bluff heads peeping up 
 at different distances through the waves which 
 compassed them with a ring of the whitest foam ; 
 while at the end of the winding, broken line, there 
 rose one rock higher thail the rest, and on top of 
 this glistened the silver tower of the light-house, 
 that, like a star -tipped wand, pointed the way, 
 
26 
 
 THE WONDERS OF SCIENCE. 
 
 as it gave the first glimpse of home to the re- 
 turning mariner.* Far beyond this, again, the eye 
 could just trace, in the mist of the distance, the 
 cloud-like islands j* studding the crystal ring of the 
 horizon, while all the rest was one wide desert of 
 water stretching away to the Western World, that 
 even the fancy was weary-winged in its struggle 
 to reach. 
 
 Nor was the scene behind the narrow tongue of 
 land that forms the very end of our island less grand 
 and solemn than that which lay before it. To the 
 southward the pathway was along the edge of a 
 precipice that the sea beneath had scooped into a 
 curve, and here, at one extremity, the ocean had 
 drilled huge caldron -like cavities in the rock,| and 
 pouring into these boiled with .a roar that made the 
 cliffs boom again with the noise. Beyond this rose 
 the majestic headland of “ Carn-y -Voel” its sum- 
 mit half veiled by a light scarf of clouds, and its tall 
 sides, built of granite cubes, rising straight as a 
 fortress \^all from out the sea. Here the ocean 
 had worked for itself a little bay, where the smooth 
 green water lay like a mirror, with the shadows of 
 the yellowish-red cliffs above it reflected deep into 
 
 * These are called the 11 Long Ships’ Rocks,” and on one of 
 them is a “ light.” British ships passing this pay one halfpenny 
 a ton, and foreigners one shilling each vessel ; the annual revenue 
 thus obtained amounting to three thousand pounds. 
 
 The Scilly Isles. 
 
 X Known by the name of “ Enys Dodnan .” 
 
YOUNG HUMPHRY’S RESOLVES. 
 
 27 
 
 the pool, and trembling, as the surface rippled, into 
 zig-zag lines that played with a thousand lights and 
 shades. On the other side of this bay a low granite 
 cliff jutted out like a buttress, the green ground 
 above sloping abruptly down ; and against this the 
 waves beat and dashed till the spray played around 
 the rocks like a cloud of smoke, and sparkled in the 
 sun delicately tinted with many a prismatic hue. 
 Here, again, the ocean had burrowed into the thick 
 granite wall, while near the verge of the cliff there 
 was a perpendicular shaft, the sides of which were 
 smooth and circular, as if they had been drilled 
 out of the solid rock ; and looking down these, as 
 down a dark well, the eye could see the white 
 waves tumbling and tossing below with a terrible 
 fury.* 
 
 On the northern side of the promontory, called in 
 Cornish “ Antyer Deweth” or the Land’s End, the 
 headlands were higher than those even on the south, 
 for there one tall rock rose out of the waves tower- 
 ing high into the air, and formed also of granite 
 cubes, which looked in the distance so like a suit of 
 mail, that it had acquired the name of the “ Armed 
 Knight and here at the very top of one of the 
 craggy summits a singular cross of rock was to be 
 seen, while as the eye travelled along the curved 
 and crumpled shore, far away to the north, it rested 
 
 * This is called in Cornish “ ToUPedn-Penwithf' which sig- 
 nifies the holed headland on the left hand. 
 
28 
 
 THE WONDERS OF SCIENCE. 
 
 on tlie point of land known by the name of “ Cape 
 Cornwall,” the outlines and tints of whose slate 
 cliffs, seen through the atmospheric veil, appeared 
 soft and blue with the haze of distance. 
 
 Despite the blocks of granite that protruded 
 through the land, like the bones of the earth itself, 
 the ground roundabout was rich in parts with 
 flowers. Now the soil was purple with the richest 
 heaths, and now it was yellow as a plate of gold 
 with the bloom of the dwarf-furze, the latter filling 
 the air with a perfume like apricots, while the 
 green patches of grass were almost iridescent with 
 the various wild flowers that peeped with their 
 delicate blossoms from out the blades. The air, too, 
 was savoury with the odour of the sea, and fresh 
 with the spray that, like a dew, brushed against the 
 cheek. Still amidst the solemn convulsion of rocks 
 and the vast belt of water which encompassed the 
 beholder as far as the sight could stretch, a feeling 
 of overpowering loneliness — a sense of one’s own in- 
 significance and helplessness, such as travellers are 
 said to feel in deserts — oppressed the mind there — 
 there , at the very brink, as it were, of one’s native 
 country — the last bit of the land with which all 
 one’s affections and associations were linked — and 
 rapt in a ghastly silence, that was broken only by 
 the moan -like booming of the monster sea, as it beat 
 into the cavities of the cliff far beneath the feet, or, 
 now and then, by the shrill shrieking of the cor- 
 
young Humphry’s resolves. 
 
 29 
 
 morant, or the whirr of some passing sea-mew’s 
 wing.* 
 
 The hoy sat, as we said, for a while staring 
 vacantly at the waves that pranced, like curvetting 
 steeds, before him, and as he did so a heavy tear- 
 drop fell now and then on the moss that spotted the 
 rock at his feet. Sometimes his lips would move, 
 though not a word escaped them, and he would 
 
 * Davy is said to have delighted as a boy in visiting the Land’s 
 End. In one of his early poems occurs the following passage, in 
 which the spot is spoken of under its Latin name, “ Bolerium : ” 
 
 “ Thy awful height, Bolerium, is not loved 
 By busy man ; and no one wanders there 
 Save he who follows Nature — he who seeks 
 Amidst thy crags and storm -beat rocks to find 
 The marks of changes, teaching the great laws, 
 
 That raised the globe from chaos ; or he whose soul 
 Is warm with fire poetic.” 
 
 “ It is surely not difficult,” says Dr. Paris, “ to understand how 
 it happened that a mind endowed with the genius and sensibility 
 of Davy should have been directed to the study of chemistry and 
 mineralogy, when we consider the nature and scenery of the 
 country in which accident had placed him. . . .Nor could 
 
 he have wandered along the rocky coast, nor have reposed for a 
 moment to contemplate its wild scenery, without being invited to 
 geological inquiry. . . . ‘How often, when a boy,’ said 
 
 Davy to me (adds the Doctor) , on my showing him a drawing of 
 the wild rock scenery of Botallack Mine, ‘ have I wandered about 
 those rocks in search of new minerals, and, when fatigued, sat 
 down upon the turf, and exercised my fancy in anticipation of 
 scientific renown.’ ” (Botallack Mine is situate at St. Just, 
 a town near to Cape Cornwall, and but a short distance from the 
 Land’s End.) “ The granite and serpentine rocks of his native 
 county were, I believe,” says Dr. John Davy, “ the first he 
 studied when he commenced the pursuit of geology, and both of 
 them were to him particularly attractive. The finest examples of 
 
so 
 
 THE WONDERS OE SCIENCE. 
 
 strike the air with his clenched fist as though a sud- 
 den resolution had crossed his mind ; then a shudder 
 would pass over his frame, and he would clasp his 
 forehead with both his hands, and sway his body to 
 and fro, as he bent his head almost to his knees. 
 Presently, after a slight pause, he would raise 
 his head, and with his neck stretched back, look 
 steadfastly at the heavens as if gazing at some 
 spirit there. And when this fit was passed, he 
 
 these rocks were within a day’s ride of Penzance ; and when he 
 visited home, a young man, he never failed paying the Lizard and 
 the Land’s End a visit, and generally in company with some of 
 his old school-fellows. I remember when a boy,” Dr. D. con- 
 tinues, “ being allowed to join one of these parties to the Land’s 
 End, and it was a merry one — as youthful parties commonly are. 
 After exploring the cliff scenery, we dined at a tavern at St. Just, 
 and I w r ell recollect the boisterous mirth indulged in when the 
 repast was concluded — the gymnastic feats attempted, the shouts 
 of applause, the unconstrained laughter, and all that abandonment 
 of spirit to mirth so common to young persons under excitement, 
 and which, excepting in youth, can scarcely be felt or enjoyed.” — 
 Life of Sir Humphry Davy. 
 
 In the commencement of a work designed by Sir Humphry 
 Davy upon “ The Geology of Cornwall,” the philosopher himself 
 gives the following description of the rocks at the Land’s End : 
 “ In the great arrangement of the masses of granite of Cornwall, 
 the rock appears composed of an immense number of blocks of 
 different sizes. This structure is nowhere more perfectly ex- 
 hibited than in the western cliffs. The incessant agency of the 
 Atlantic, its storms and its waves, have washed away or destroyed 
 all the loose materials of the shore, and left abrupt eminences of 
 rock from 50 to 360 feet in height. The arrangement of the granite 
 is in masses which approach to the cubical form, having, however, 
 rounded edges, heaped upon each other. . . . The masses 
 
 are grand, their colours uniform, and their uniformity' increases 
 the effect upon the eye ; while the arrangements of this kind have 
 
YOUNG HUMPHRY S RESOLVES. 
 
 31 
 
 would resftme his seat, and clasp his hands as in 
 prayer. 
 
 Suddenly the hoy started to his feet, crying, 
 “ Yes, I’ll do it — that I will. I will rescue them 
 all — every one — from the poverty that threatens 
 them. I have promised my dead father to do so. 
 I have prayed God to give me the strength and 
 firmness to carry out my purpose, and in a few 
 years our home shall be as happy as it’s wretched 
 
 a peculiar wildness and sublimity. Nowhere is it seen upon a 
 greater scale, or in a more magnificent assemblage of forms, than 
 from a point between the Land’s End and Castle Treene. Both 
 these grand promontories appear extending into the Atlantic; 
 the cliffs between them are abrupt and lofty ; the waves are 
 broken by a number of small island rocks, which are scattered 
 along the shore. The few portions of soil that appear above the 
 cliff are covered with short green grass, tufted with heath and 
 furze, which, in the autumn, present mixed hues of purple and 
 gold. The rock throughout is of a uniform yellowish red, the 
 tint perfectly contrasted to the blue-greens of the sea.” (Castle 
 Treene, or “ Castle Treryn,” as it is more correctly written, is 
 a headland beyond “ St. Levan churchtown,” as it is sometimes 
 called — though the chapel which formerly stood there has been 
 many years since washed away by the sea, the steps alone now 
 remaining. St. Levan lies a little to the eastward of the head- 
 land called “ Tol Pedn Penwith .” A short distance from St. 
 Levan is u Port Carnow Cove,” which is bounded on the eastern 
 side by rocks that jut far into the waves, and rise to a great 
 height, being heaped one on another, in magnificent order. Here 
 stands the noble headland called “ Castle Treryn,” above whose 
 summit two huge slanting and imposing masses of granite pro- 
 trude. There is a fissure between these masses leading to a 
 smaller group of granite rocks, on the top of which the huge 
 Logan stone (weighing some 65 tons) stands so delicately poised, 
 that by clambering to a fearful height at one of the angles, it may 
 be made to sway to and* fro with the least force. 
 
32 
 
 THE WONDERS OF SCIENCE. 
 
 now. I feel as if I had just woke from a long 
 dream. What a thoughtless, idle fool, I’ve been ! 
 but it’s past — never to return. Poor mother ! I’ve 
 cost her many a tear, I know, of late. How have 
 I wasted this last year, when I should have been 
 at some business seeking the means of adding to 
 my mother’s comforts, instead of lessening the little 
 that is left her at such a time as this ! If I had 
 only worked instead of squandering my time in 
 silly pleasures, I might now have been a help to 
 her rather than the wretched burden I am — with- 
 out the power to earn a crust for myself. What do 
 I know that is of use to any one ? Who would 
 give me a penny for anything that I can do ? and 
 yet I’m old and strong enough to get my own living. 
 Oh, shame ! shame ! that I, at my time of life, 
 should have to take from poor mother’s little store. 
 If I’d had a proper spirit, I should have felt this 
 long ago: but no matter, it’s ended now; and I’ll 
 go to work and so fill my mind with knowledge 
 that mother shall soon be as pleased about me, as I 
 know, poor thing ! she has been pained of late. Yes, 
 and father will watch over me ; I know he will. 
 Oh ! if I could only have changed before he died, 
 what a comfort it would have been to him in his 
 last moments : but as it was, I, like a wretch, let 
 him leave me in doubt as to what was to become of 
 me. Why didn’t I wake up before ? If it had 
 only been a month ago, he might have felt no pain 
 
young Humphry’s resolves. 
 
 83 
 
 on my account. Oh, shame ! shame ! but, thank God, 
 I’m different now, and I’ll go back home and tell 
 mother all I mean to do. I’ve the power in me — I 
 know I have. I’ll go back and tell her not to 
 grieve, and that I’ll do all I can to help her and 
 my brother and sisters for the future.” * 
 
 * Dr. John Davy says, “The greater part of the year fol- 
 lowing” (the period of his quitting Dr. Cardew’s school at 
 Truro, which Humphry did at the age of fifteen, when his school 
 education was considered as complete) “ he was, I believe, in an 
 unsettled state, studying in a desultory manner, by fits and starts, 
 and yielding to the allurements of occasional dissipation, and the 
 amusements wdiich constitute the delight of active youth — as 
 fishing, shooting, swimming, and solitary rambles. This teas 
 perhaps the most dangerous period of his life , and in conversation 
 with me he has so spoken of it . Amusement threatened for a time 
 to obtain the mastery, and keep him down to the common level ; 
 but his good genius triumphed, and, after a few months’ vacilla- 
 tion, he applied himself in earnest to the cultivation of his mind 
 and to the acquisition of knowledge ; and the flame once kindled 
 burnt on till it expired in death.” Speaking of the circumstances 
 which induced Humphry to relinquish all his boyish habits about 
 the period of his father’s death, his brother says: — u This 
 event , probably, had a powerful effect in giving steadfastness to 
 his resolution , and I am quite certain that the circumstances of 
 his family became with him an additional and powerful motive to 
 exertion .” 
 
 “ Like most young persons, Humphry when a boy,” says Dr. 
 John Davy, “was fond of declaiming, and indulged in it in his 
 solitary walks and rambles. On one occasion it is recorded of him , 
 that, on his way to visit a poor patient in the country ” (during his 
 apprenticeship), “in the fervour of declamation, he threw out of 
 his hand a phial of medicine which he had to administer, and that 
 when he arrived at the bed-side of the poor woman he was sur- 
 prised at the loss of it. The potion was found the next day in a 
 hay-field adjoining the path” (p. 55). 
 
 D 
 
34 
 
 THE WONDERS OF SCIENCE. 
 
 CHAPTER III. 
 
 HUMPHRY AND HIS MOTHER. 
 
 The resolution once formed, young Humphry 
 hastened to convey the glad tidings to his mother, 
 and as he rode along he kept talking to himself all 
 the way, running over the many “ fine things” he 
 meant to do for the future, and dreaming that some 
 day he might perhaps become distinguished for his 
 learning and wisdom. He amused himself, too, by 
 speculating as to what he would do with his money if 
 he ever got to be rich. He would have his little bro- 
 ther John well educated then, and comfortably started 
 in life. Yes ! and he would give up his share in the 
 property at Yarfell to his mother and sisters — that 
 he would do first of all ; and if he grew to be? a 
 very wealthy man, he would give a certain sum of 
 money to the Grammar-school, so that the boys 
 might have a holiday every year on his birthday — 
 he would like to be able to do that, for then he 
 would be remembered by them as long as the school 
 lasted. Further, he would give something a year 
 to his aunt Sampson’s Phillis, and his aunt Millett’s ~ 
 maid as well. Poor Mary Launder and Betty 
 
HUMPHRY AND HIS MOTHER. 
 
 35 
 
 White should get something, too ; and he would 
 have a number of old pensioners besides, that had 
 known him when he was young. He would take 
 care, moreover, that his pony Derby and his dog 
 Chloe wanted for nothing in their old age, and 
 wherever he might be he would have a box of 
 apples sent him at Christmas from the tree he had 
 planted in the garden when he was a little fellow.* 
 On reaching the humble farm at Varfell, Hum- 
 phry found his mother seated beside a table, the 
 
 * The greater number of these resolves were fulfilled in after- 
 life. Dr. John Davy says : — “ The interest he took in me more 
 resembled that of a father than a brother, and it is with peculiar 
 pleasure I reflect on his various kindnesses — my numerous obli- 
 gations, many of which were delicately concealed at the time — his 
 valuable hints and generous regard to my studies, leaving me free 
 to follow the bias of my own mind — and his excellent advice in 
 respect to my conduct, in which was always infused a native 
 nobleness of sentiment well adapted to stir up virtue in a young 
 mind.” In one of his letters to his brother, Sir Humphry says, 
 — “ You must study your own plans with respect to study. Pray 
 do not care about the expense, if it adds anything to the comfort 
 or respectability of your situation. I will, if you like, send you 
 40Z. a year, in addition to what my mother sends you. My dear 
 John, let no difficulties alarm you; you may be what you please. 
 Let no example induce you to violate decorum — no ridicule pre- 
 vent you from guarding against sensuality or vice. Live in such 
 a way that you can always say the whole world may know what I 
 am doing.” 
 
 Dr. Paris says: — “No sooner had Davy found himself in a 
 situation which secured for him the necessaries of life, than he 
 renounced all claims upon his paternal property in favour of his 
 mother and sisters .” In a letter to one of his sisters, 'Davy says : 
 — “ I enclose a one-pound note, which you will lay out in books or 
 in anything else you like. I enclose another one-pound note, which 
 I wish to have disposed of in the following manner : — “ To Mary 
 
38 
 
 THE WONDERS OF SCIENCE. 
 
 top of which was black with a hillock of little 
 skirts and bodies that she had been busy making up 
 for the children’s week-day wear. The quick eye 
 of the boy could distinguish as he glanced at the 
 pile of mourning that the gloss of the bombazeen 
 was dulled in places with the tears that had fallen 
 upon it. 
 
 Humphry, from a sense of the grief that per- 
 vaded the house, had entered the room so softly 
 that his presence was unperceived by the widow, and 
 
 Launder, 5s. ; to Betty White, 5s. ; and with the rest you will buy 
 some ribbons or little articles of dress for the Doctor’s Jenny, my 
 aunt Sampson’s Phillis, my aunt Millett’s maid, and my mother’s 
 servant, as New-year’s gifts.” In another letter he writes thus : 
 “ I enclose a ten-pound note, which I beg you will lay out in the 
 way you think best for my sister’s children and any old pensioners 
 that knew me in my youth.” “ No Swiss peasant,” says Dr. Paris, 
 ‘ * ever sighed more deeply for his native mountains than did Davy 
 for the scenes of his early years. He entreated his nurse (when 
 ill at the Royal Institution) to convey to his friends his ardent 
 wish to obtain some apples from a particular tree which he had 
 planted when a boy, and he remained in a state of restlessness 
 and impatience until their arrival.” Moreover, it should be 
 stated, that, in addition to his will, he left at his death a paper 
 of directions, which have been religiously observed by his widow. 
 In these he desires that the interest arising from 100/. stock may 
 be annually paid to the master of the Penzance Grammar-school, 
 on condition that the hoys may have a holiday on his birthday. 
 “ There is something,” adds Dr. Paris, “singularly interesting 
 in this favourable recollection of his native town and of the asso- 
 ciations of his early youth. It adds one more example to show, 
 that, whatever may have been our destinies, and however fortune 
 may have changed our condition, where the heart remains un- 
 corrupted we shall, as the world closes upon us, fix our imagina- 
 tions upon the simplicities of our youth, and be cheered and warmed 
 by the remembrance of early pleasures.” 
 
HUMPHRY AND IIIS MOTHER. 
 
 87 
 
 for a minute or two he stood watching his mother 
 as she sat there with her flooded eyes fixed intently 
 on the large carved oak-chair (her late husband’s 
 handiwork) that stood beside the mantel-piece. Her 
 cheek rested on her hand, and it was plain by the 
 fixedness of her gaze that the seat was no longer 
 empty to her, and that her mind was far away in 
 the past. 
 
 The sight of that sad wife, widowed almost in 
 her youth, was sufficient to have touched many a 
 stouter heart than young Humphry’s. The widow’s 
 hair was still unsilvered by age, and its blackness 
 contrasted forcibly, and even painfully, with the 
 close white muslin cap that half concealed it. The 
 dead black of the crape made her cheek as pale 
 as marble, while the tears that dewed her eyes gav.e 
 them an almost glassy look, so that they seemed 
 jettier than usual. Her face, though young in 
 years, was prematurely old in expression, for the 
 features, which were naturally well formed, were 
 pinched ; and there was an air of mild resignation 
 over the countenance that told you the poor woman 
 had long ago learnt to bear affliction, almost with- 
 out complaint. Nor did it need a second glance to 
 discern the tenderness and affection of her nature,* 
 
 * “In all the various situations of life in which my mother was 
 placed,” says Dr. John Davy, “ she so conducted herself as to 
 gain the regard and good-will of every one. She possessed a 
 most kind and affectionate heart, a pious mind, sound under- 
 standing, and perfect integrity. She was devoted to the perform- 
 
38 
 
 THE WONDERS OF SCIENCE. 
 
 — for though there was a settled melancholy in her 
 face, there was still so much kindliness in its ex- 
 pression that the heart could not help extending to 
 her the sympathy that it knew she would be the 
 first to afford to others who had seen as much 
 trouble as she herself had in the course of the few 
 years that had passed over her head. 
 
 Humphry drew towards his mother’s chair, and 
 resting against the back curled his arm gently 
 about her neck. So unexpected, however, was the 
 embrace, that the widow shrieked with alarm as she 
 was suddenly roused from her melancholy reverie. 
 
 The next moment, pleased at the idleness of her 
 fright, she clasped the pet boy to her ; and while 
 the tears gushed from her eyes she kissed him 
 again and again, as though she loved him the more 
 now that he and her other children were all that 
 she had left to engross her affection. 
 
 “ What ! in tears again, mother ? ” said Hum- 
 phry, in a tone of kindly remonstrance. “ Hay, do 
 
 ance of all her duties, and was remarkably free from all guile and 
 foolish pride. When she became a widow, she w T as in her 
 thirty-fourth year, with five children, all of whom were still to be 
 educated, excepting Humphry, her eldest son. Her income at 
 this time was about 150 1. a-year, and it was encumbered with a 
 debt of about 1300Z., contracted by my father chiefly in conse- 
 quence of losing speculations in mining. Her good resolutions 
 did not fail her on this trying occasion ; she met all her difficulties 
 with courage and prudence.” 
 
 Dr. Paris, speaking of Davy’s mother, says , — 11 She was 
 remarkable for the placidity of her temper and for the amiable 
 and benevolent tendency of her disposition.” 
 
HUMPHRY AND HIS MOTHER. 
 
 not grieve,” lie added, as the widow rested her head 
 on his bosom, “ I have come to promise you that I 
 will do all in my power for my brother and 
 sisters.” * 
 
 “ But what C2LH 7/OU do, Humphry, my good lad ? ” 
 asked the mother, as she looked up through her tears 
 and smiled at the youth. “ It will take you some 
 years before you can earn a livelihood, and even 
 then perhaps you will gain only sufficient for your 
 own wants. What is to become of my little ones is 
 more than I can bear to think of. How you, too, 
 Humphry, are to be put out in the world, I’m sure 
 I cannot say. My means, when all the debts are 
 paid, will be only 100/. a-year, if that.” 
 
 “ There, there ; have no trouble on my account, 
 mother,” returned the lad. “ I’ve made up my 
 mind to lay aside all my idle habits, and to set hard 
 to work at something directly — though I cannot tell 
 what, just now; and you shall see I won’t be long 
 before I make you all happy here.” 
 
 The mother half laughed at the sanguineness of 
 her son, and said, when she had kissed him for his 
 kindness, “ But you talk like a boy, Humphry. You 
 don’t know how hard it is to earn money yet.” 
 
 “Yes I do, mother,” replied the determined 
 
 * “ My brother,” says Dr. John Davy, “ at the time of my 
 father’s death was sixteen years old. Seeing her (Mrs. Davy) in 
 great affliction, he, in a very affectionate manner, begged her 
 1 not to grieve,’ saying that 1 he would do all he could for his 
 brother and sisters .’ ” 
 
40 
 
 THE WONDERS OF SCIENCE. 
 
 youth, as he pressed her hand. “ But I feel I have 
 the power in me, and I’ll do it, you shall see — all by 
 myself too — aye, that I will, if I have to study 
 night and day. You don’t know what a lesson 
 poor father’s death has been to me. I never saw 
 you in grief before, and all this last week my mind 
 has been at work, for your tears were more than I 
 could bear. Not a night of late has past but I 
 have reproached myself over and over again that I 
 had wasted the last year of my life, instead of doing 
 something that would have given me the power to 
 help you at such a time as this. When I heard Mr. 
 Tonkin, too, talking with you the other day about 
 the money you would have to live upon, and heard 
 him say that it was high time I should cease being 
 a burden to you, — yes, those were his words, 
 mother — a burden ” (and the boy would have 
 turned away from the widow, but she held his 
 hand) “ I felt the blood rush into my face with 
 shame, and a new spirit came over me. I didn’t 
 say anything to you, mother, at the time, because I 
 thought I could hardly trust myself ; but I went on 
 thinking I was a burden to you, and the heaviest 
 burden of all, too. So I kept brooding and brood- 
 ing it over, until at last I made a solemn deter- 
 mination that, instead of a burden, I would be a 
 help to you and my brother and sisters for the 
 future. I have sworn it, mother ! I have promised 
 my poor father to do so this very day — alone 
 
HUMPHRY AND HIS MOTHER. 
 
 41 
 
 among the rocks I made the vow, and I’m sure he 
 heard me, for I feel as I never felt before, and I 
 know I’ve the power to do as I have said.” 
 
 The mother in her delight hugged the boy 
 passionately to her bosom, and as her tears fell 
 thick and hot upon him she said through her sobs, 
 “ You have the power, I know, Humphry ; and if 
 this sad bereavement which has come upon us all 
 does but stir you to make use of the genius that is 
 in you, it will be indeed almost a recompense for 
 the heavy loss we have sustained. When you were 
 but a child, I used to tell your dear father of the 
 bright hopes I had of you, Humphry, and that 
 I was sure you would be very clever some day ; 
 though he, poor man ! only smiled at my words, and 
 thought it was my over- fondness that made me 
 fancy as much, saying all mothers did the same. 
 But I knew differently, Humphry ; I could see you 
 were not like other children, and even from an in- 
 fant there was hardly anything babyish about you. 
 When you were only five years old you made rhymes 
 of your own, and used to recite them in the Christmas 
 gambols, and I knew there was no little thing of that 
 age that could do the same thing in these parts.” 
 
 “Yes, I’ve often heard you say so, mother,” 
 added the boy, smiling at the youthful reminis- 
 cence. 
 
 “ You were a very forward child— from a baby I 
 may say, Humphry,” continued the proud mother, 
 
42 
 
 THE WONDERS OF SCIENCE. 
 
 as she passed her fingers through the lad’s hair, and 
 brushed it from his forehead, — for she half forgot 
 her sorrow as the recollection of her pet boy’s feats 
 stole, one after another, across her mind. “ Why, 
 you were only nine months old when you walked 
 off, all by yourself ; and you could speak as well, 
 and fluently, as a little man, before you were two 
 years of age. Shall I tell you, too, what you said 
 when your sister Kitty was born? — little sharp 
 thing as you were ! The servant had been assuring 
 you day after day, that when the baby came you’d 
 be no longer petted in the way you had been,— for 
 then, as the maid said, ‘ your nose would be put out 
 of joint.’ This seemed to make a great impression 
 upon you, for directly you saw little Kitty you put 
 your chubby fat hand up to your face, and cried, 
 4 Mamma ! my nose not out of joint at all.’ ” 
 
 “ Did I?” laughed Humphry. 
 
 “ Yes, that you did,” said the mother. “ Ay, 
 and before* you had learnt to write you used to 
 copy the figures in ‘iEsop’s Fables,’ and print the 
 names of them in big letters underneath. I really 
 think, too, you couldn’t have been more than four 
 years old when you could recite a good part of 
 6 Pilgrim’s Progress.’ All I know is, you did so 
 before you could well read the book; for your 
 memory was so great, that anything you had heard 
 once or twice you could repeat, almost without a 
 mistake, afterwards ; and when you were sent to 
 
HUMPHRY AND HIS MOTHER. 
 
 43 
 
 Mr. Bushell’s school — you remember old Mr. 
 Bushell, Humphry — you made such rapid progress 
 there in your reading and writing, that though you 
 were only six years of age, the old gentleman, 
 against his own interest, recommended your poor 
 father to remove you to the Grammar-school.”* 
 
 “ When you could read, too, I often watched 
 
 * * 1 It is remembered,” says Dr. John Davy, speaking of Sir 
 Humphry’s infancy, “ that he walked off (to use a nursery 
 phrase) when he was just nine months old ; and I have been told, 
 that before he was two years of age he could speak fluently. 
 About this time my eldest sister was born, and he was told by a 
 servant, that on her appearance ‘ his nose would be put out of 
 joint.’ On seeing the baby, it is related of him, that he put his 
 hand to his nose, and said, ‘ Mamma, my nose not out of joint.’ 
 Before he had learned to write, he amused himself with copying 
 the figures in ‘ HSsop’s Fables,’ and under his drawings, in great 
 letters, he contrived to give them their names. His memory 
 was very retentive, in proof of which it is handed down in the 
 family, that when very young he could recite a great part of ‘ Pil- 
 grim’s Progress,’ even before he could well read it. I believe 
 that, like Pope, he lisped in numbers. I remember hearing my 
 mother say, that when scarcely five years old he made rhymes, 
 and recited them in the Christmas gambols. His disposition 
 as a child was remarkably sweet and affectionate. . . The first 
 school he was sent to was that of a Mr. Bushell, at which reading 
 and writing only were taught. This master, then an old man, 
 remarking the rapid progress of his young pupil (he was then 
 six years old) , in a very disinterested manner recommended my 
 father to remove him to the Grammar-school.” 
 
 “ It is a fact,” says Dr. Paris, “worthy, perhaps, of being 
 recorded, that Humphry Davy would, at the age of five years, 
 turn over the pages of a book as rapidly as if he were merely 
 engaged in counting the leaves or in hunting after pictures, and 
 yet, on being questioned, he could generally give a very satis- 
 factory account of the contents. The same faculty was retained 
 by him through life.” 
 
44 
 
 THE WONDERS OF SCIENCE. 
 
 yon at your books, and saw you turn over the 
 pages so fast, that I fancied you were merely 
 counting them, or hunting for pictures; but on 
 talking to you about the book I used to find, to 
 my astonishment, that you had read it through 
 in that short time, and that you really knew all 
 about it, and could give a much better account of 
 it than children who might have taken hours, or 
 perhaps days, to get through it.” 
 
 Humphry drew closer to his mother, and pressed 
 her hand between his palms as he looked up in her 
 face, and smiled with delight to hear her run over 
 all the feats of his youthful genius ; for with the 
 history of each little wonder he felt the faith he 
 wished to have in his own powers grow stronger in 
 him, and he shook his head proudly as he inwardly 
 thought of the greater wonders he would achieve 
 in the time to come. 
 
 “ Go on, mother,” he said, as he seated himself 
 on the stool at the widow’s feet, “ tell me some 
 more things I used to do when I was a little 
 fellow — tell me some more, they fill me with the 
 same hope as you say they did you, and I want 
 to have all the trust I can in myself; for I’ve made 
 up my mind to be a great man, and if I doubt my 
 power to accomplish the task I have set myself, 
 I shall, perhaps, give it up almost at the first, 
 difficulty. Tell me something more, mother; I 
 want all the faith in myself you can give me.” 
 
HUMPHRY AND HIS MOTHER. 
 
 45 
 
 “ I wish I could give you as much confidence in 
 your own powers, Humphry, as I have in them,” 
 returned the widow, 6 4 though now you begin to 
 speak with all the aspirations I have longed to see 
 coming upon you ; and for the last year I cannot 
 tell you how grieved I have been to behold one, of 
 whom I had formed such high hopes, giving him- 
 self up to pleasures that serve to breed only habits 
 of thoughtless amusement rather than wise reflec- 
 tion.” 
 
 “ I know I have pained you, mother,” added 
 Humphry, “ but it’s all at an end now. You re- 
 member when I was at the Grammar-school, how 
 Mr. Coryton used to pull my ears for not minding 
 the lessons he set me. But do you know, mother, 
 I have often thought, that though I learnt little at 
 Mr. Coryton’s school, it was, perhaps, better after 
 all that I should have been left to teach myself ; 
 for what we learn from our own liking, we seldom 
 forget ; and I am sure I remember more about the 
 books I have had from Mr. Tonkin, and that I used 
 to read through one after the other as fast as I 
 could get them, than all the Latin and Greek I was 
 forced to get by heart at school.”* 
 
 * “ The Rev. Mr. Coryton (the master of the Grammar-school) 
 was a man of irregular habits, and ill-fitted for the office of teach- 
 ing youth. He was occasionally severe, and punished heavily 
 slight offences. Pulling the boys* ears was practised by him in 
 the most capricious manner, and my brother was too frequently a 
 sufferer from this infliction. It is recorded of Humphry Davy 
 
46 
 
 THE WONDERS OF SCIENCE. 
 
 “ Ah, hut Mr. Coryton,’’ interrupted the mother, 
 
 “ was a man little fitted for teaching youth, 
 Humphry. He was careless about the boys’ studies, 
 and often very severe for the slightest faults. I 
 remember once you went to school, unknown to me, 
 with a large plaster on each ear, and when Mr. 
 Coryton asked you 4 what was the matter with your 
 ears,’ you told him ‘ that you had put the plasters on 
 to prevent a mortification.’ But if you didn’t stand 
 very well with the master, you were at least in high 
 favour with the boys, Humphry, for you used to do 
 the Latin and English verses for half the school ; 
 and as for writing valentines and love-verses, why 
 I am sure your play-time was mostly taken up with 
 
 that he appeared before Mr. Coryton with a large plaster on each 
 ear, and that when asked by his master ‘ what was the matter 
 with his ears,’ he replied with a very grave face, ‘ that he had put 
 the plasters on to prevent a mortification.’ ” — Dr. John Davy , 
 p. 14. In a letter to his mother, Sir Humphry Davy says, 
 speaking of this school, “ I consider it fortunate that I was left 
 much to myself as a child, and put upon no particular plan of 
 study, and that 1 enjoyed much idleness at Mr. Coryton’s school. 
 
 I perhaps owe to these circumstances the little talents that I have, 
 and their peculiar application. What I am, I have made myself. 
 
 I say this without vanity, and in pure simplicity of heart.” 
 Davy seems, indeed, to have been more distinguished out of 
 school, and by his comrades, than by any great advance in learn- 
 ing. “ From his facility in composing Latin and English verse,” 
 says his brother, “ his assistance in these exercises was often 
 requested, even by boys much older than himself ; and in writing 
 valentines and love-letters, he shone so pre-eminently, and gave 
 his aid so willingly, that he is said to have been generally resorted - 
 to, on all emergencies of boyish loves. Another cause of popu- 
 larity among his comrades was his power of diverting them by 
 
HUMPHRY AND HIS MOTHER. 
 
 47 
 
 scribbling rhymes to first Miss This and then Miss 
 That for some little urchin in a jacket, who fancied 
 himself to be smitten with the young lady. Then 
 of an evening you were always to be found under 
 the balcony of the Star Inn — for you were shel- 
 tered there — with a group of boys round about you ; 
 and, if there happened to be a cart on the spot, you 
 would be sure to mount it, and there you’d remain 
 narrating all kinds of romantic stories to the little 
 mob of school-fellows who came regularly to listen 
 to you. I never knew such a boy for story-telling 
 as you were, Humphry ! I have many a time heard 
 you make up the strangest kind of tales out of your 
 own head ; and while I was in the parlour at work, 
 
 telling them stories ; and so attractive were the tales, commonly 
 of wonder and terror, which he related, that they were in the 
 habit in an evening of collecting at a particular place to wait for 
 him, as under the balcony of the Star Inn, which afforded shelter, 
 and where, if there happened to be a cart, he would get into it, 
 and hold forth to his young audience.” {Idem, p. 15.) “ The 
 
 earliest indication that I am aware of,” says Davy’s brother, 
 “ which he showed of his fondness for experimenting, was in 
 making fire -works. My eldest sister well remembers that she 
 was his assistant in this undertaking, and that their workshop 
 was an unfurnished room, in which, in bad weather, the Rev. Dr. 
 Tonkin (the elder brother of Mr. John Tonkin, the friend of our 
 family), then advanced in age and a valetudinarian, took exercise 
 on his chamber-horse — a large arm-chair attached to spring- 
 boards, which boards served for a table for compounding the in- 
 gredients of the squibs and crackers.” “Davy,” says Dr. Paris, 
 speaking of his youthful amusements, “ was in the habit of pre- 
 paring a detonating composition, to which he gave the name of 
 1 thunder powder,’ and which he would explode on a stone, to the 
 great delight of his young playfellows ” (p. 5). 
 
48 
 
 THE WONDERS OF SCIENCE. 
 
 I used to listen to you, as you and young Batten 
 sat out in tlie porch, with your arms curled round 
 each other’s necks, and you would be there hour 
 after hour ; for you were never tired of inventing, 
 nor he tired of listening to the stories of wonder 
 and terror you both delighted in.” 
 
 “ I can remember it all well, mother,” added 
 Humphry. “ And do you recollect how fond I was 
 of making fireworks, and how Kitty used to help me 
 till her fingers were as black as sticks of liquorice 
 with the gunpowder ; and how we used to mix up 
 the composition for our squibs and crackers on the 
 spring-boards of old Dr. Tonkin’s chamber-horse 
 that stood in the empty room, when we lived at 
 Penzance, and that the poor old gentleman used to 
 take his exercise upon in wet weather ? ” 
 
 “ Yes, that I do, Humphry,” smiled Mrs. Davy ; 
 “ and many a time you have nearly frightened me 
 out of my wits with your 6 thunder-powder,’ as 
 you called it, which you used to delight in putting 
 under the chairs, so that the moment any one sat 
 down, there was such an explosion that everybody 
 in the room felt as though all their bones had 
 been suddenly broken. Your poor father only per- 
 ceived in such tricks an idle, thoughtless disposi- 
 tion ; but women see more keenly into character 
 than men, and I not only recollected, but knew, the 
 quick boy you were, and how rapidly you could 
 acquire anything to which you applied yourself ; 
 
HUMPHRY AND HIS MOTHER. 
 
 49 
 
 besides, I bad noticed your inventive turn from 
 a child, and the force of your imagination in the 
 stories you made up and the poems you had written 
 — for at twelve you had composed an epic that I 
 have by me still ; — and all these things gave me 
 assurances that one day you would take a foremost 
 place among the great men of the country. A 
 mother’s heart may have led me to have these 
 hopes of you, Humphry ; my understanding, how- 
 ever, convinced me that they were not mere dreams 
 begotten by affection, but conclusions calmly come 
 to after narrowly watching — as a mother only can 
 watch — every little turn and trait in your cha- 
 racter.” 
 
 “ No, mother ! ” burst out the boy ; “ they are 
 not dreams, but clear foreseeings ; and you yourself 
 shall witness the realisation of them before many 
 years have passed.” 
 
 “ God grant that I may live to do so, my boy,” 
 murmured the widow, as she raised her eyes to 
 heaven. “ ‘ Life,’ as some wise man says, ‘ has 
 few better things to give than a talented son,’ and 
 it seems to me there can be no greater pleasure 
 to a mother’s heart than to witness the genius 
 which she has watched bud and expand from year 
 to year ripen into excellent wisdom, and come to be 
 acknowledged and reverenced by the world at 
 large — no joy more exquisite to a woman’s nature 
 than that which she must surely experience on 
 
50 
 
 THE WONDERS OF SCIENCE. 
 
 finding that the mind which she had tended from 
 its very dawn — catching up the first glimpses of 
 intellect, and garnering them in her bosom as house- 
 hold wonders and bright things of promise — has 
 fulfilled all her best hopes, and that the visions she 
 had formed of the fame and honour that were to 
 attend her boy in after-life have not been mere 
 dreams of her admiration or her pride. But rather, 
 that the being whom she has loved, and wished to 
 have loved by others, lives to be at length praised 
 and esteemed by all, for the talents and virtues that 
 she was the first to notice and to foster. This, 
 Humphry, is the brightest and sweetest reward a 
 woman can meet with in her old age ; and, having 
 reaped it, she parts from life with a sense of duty 
 fulfilled, and a feeling that the affection with 
 which she welcomed her child into existence, 
 and the care with which she tended him in his 
 youth, have not been unprofitably bestowed, but 
 repaid her in the richest coin the world can offer to 
 a parent.” 
 
 Humphry for a while remained in silence, while 
 his mother’s words sank deep into his soul ; then 
 he said, softly, “ May it be my proud lot, mother, 
 to render you such a reward. I am thankful to 
 the Creator that I have passed through the most 
 dangerous portion of my life with few errors, and 
 I hope to devote myself for the future to pursuits 
 useful to mankind, and which in after years may 
 
HUMPHRY AND HIS MOTHER. 
 
 51 
 
 perhaps obtain for me the applause of enlightened 
 men.”* 
 
 The widow laid her hand on the boy’s head as he 
 sat at her feet, and she said, solemnly, “ My blessing 
 be on you, my son. May God give you strength to 
 maintain your noble purpose ! ” 
 
 Then she threw her arms about him, and bursting 
 into a flood of tears, cried, “ Oh, my boy ! my boy ! 
 you know not how happy you have made me. 
 Your words are like oil to my wounded heart. 
 Sometimes, of late, I have wondered why it should 
 please Providence to visit me so sorely — me , who 
 never knowingly injured any one in thought or 
 act. And yet, even almost in my infancy, I was 
 deprived of father and mother at one blow, so 
 that the very features of my parents are unre- 
 membered by me, and the blessing of their love 
 a joy I was scarcely allowed to taste. And now, 
 before my own children are able to help them- 
 selves, he who would have been their best pro- 
 tector is snatched from me, and I again am alone 
 in life, bereft of the love and care I had hoped 
 
 * The above are Davy’s own words, taken from a fragment of 
 a letter which his brother says exists in one of Sir Humphry’s 
 note-books, kept during his youth, and which was addressed to 
 one of his early home friends, the letter itself being descriptive of 
 his escape from the vices which are the most seductive to youth in 
 towns. “ An active mind,” he writes, 11 a deep ideal feeling of 
 good, a look towards future greatness , has preserved me from 
 these.” 
 
52 
 
 THE WONDERS OF SCIENCE. 
 
 to share for years to come, and left with five 
 young children, and only a woman’s arm to shield 
 them from the bufferings of the world. It needs 
 no little faith in the goodness of God, Humphry, 
 to believe that there is mercy in all this ; and often, 
 in the bitterness of my tribulation, I have been 
 wicked enough to doubt it : for I, with my mind dis- 
 tempered by suffering, could discover no trace of 
 kindness in it all. But now I see the purpose of 
 my affliction. It was to stir you, Humphry, to be 
 a protector to your brother and sisters — to develop 
 the high and noble nature with which you had been 
 gifted, .and to raise up to me a son, the glory of 
 whose future renown should be something like a 
 recompense to me for the partner I have lost — a son 
 who should be the means of contributing not only 
 to the comfort and happiness of my children, but to 
 the welfare of mankind at large. Yes ! I under- 
 stand the reason of my trials now: and look you, 
 my dear boy, how good comes of evil. The first pri- 
 vation I and your aunts suffered was the means of 
 creating for us such a friend as is seldom met with 
 in this world ; I mean Mr. Tonkin, who was not 
 only a father to me and my sisters, but has ex- 
 tended his goodness to our children — for you, Hum- 
 phry, have passed more of your time with him than 
 under your poor father’s roof. And now, no sooner 
 is my husband taken from me than you — the giddy 
 boy, who had of late been so absorbed in pleasure 
 
HUMPHRY AND HIS MOTHER. 
 
 53 
 
 that I had almost begun to think the hopes I 
 had formed were nothing but a mother’s vanity — 
 become quickened in an instant with a new nature, 
 as if suddenly exalted into manhood, instinct with 
 generous purposes and noble determinations ; and, 
 though you are but a mere youth in years, ready 
 to supply the place of a father to your brother and 
 sisters, and a friend and protector to me.” 
 
54 
 
 THE WONDERS OF SCIENCE. 
 
 CHAPTER IV, 
 
 THE FIRST DRINK AT THE WELL. 
 
 A few months had wrought a great change in the 
 household at Varfell. 
 
 The widow, when the stupor of her grief had 
 passed away, and the mental absorption of her first 
 sorrow had given place to the calm reflection of 
 melancholy, soon began to see that the comforts 
 and education of her children demanded energy 
 rather than tears from her. 
 
 Then came the struggle. What could she do to 
 help them ? And what would the people think 
 and say if this or that were done ? 
 
 But Mrs. Davy was not the woman to be 
 daunted by the petty exultation of neighbours ; so 
 that when an opportunity offered for her to embark 
 in business as a milliner in the neighbouring town, 
 it cost her hardly a pang— free as she was from 
 all silly pride — to sink from the worldly rank of 
 the gentlewoman into the humbler station of the 
 trader. 
 
THE FIRST DRINK AT THE WELL. 
 
 55 
 
 Accordingly, after consulting with Mr. Tonkin 
 upon the matter, she was duly installed, in con- 
 junction with a young French lady, as dressmaker 
 and milliner, in a little shop in the town of Pen- 
 zance. 
 
 Nor was Humphry long in finding a fitting occu- 
 pation. Mr. Tonkin, to whom the youth had com- 
 municated all his determinations, and who loved 
 the youth almost as if he had been a child of his 
 own (for the greater part of Humphry’s life had 
 been passed with the old gentleman), was as 
 pleased as the widow had been to hear of the new 
 spirit that had come upon the lad ; and although 
 the boy’s foster-father was not so sanguine as his 
 mother had been of the world-wide renown that 
 awaited Humphry in after life, he had, neverthe- 
 less, sufficient faith in the talents of the youth to 
 believe that he might, by application, ultimately 
 win his way to competence and respect among the 
 circle of his native town. Accordingly, when the 
 ardent boy spoke to the calm old man of the fame 
 and honours he had made up his mind to gain 
 throughout Europe — saying, with all the fervour of 
 a boy-poet’s nature, that he was resolved his mind 
 should become a light to all nations, and that his 
 name should be linked with noble associations in 
 every enlightened country, Mr. Tonkin smiled 
 incredulously (but still with good humour) at the 
 
56 THE WONDERS OF SCIENCE. 
 
 ambitious dreams of the lad, and told him he was 
 afraid one so young as he knew not how difficult it 
 was to excel, even in the most trivial thing, when 
 we had the entire world for rivals ; and that 
 powers which appeared great in the narrow circle 
 of our own family, grew less and less as the arena 
 of competition was widened. Therefore, if the 
 youth, instead of regarding the whole of Christen- 
 dom as the theatre in which his future powers 
 were to be displayed, would but limit his views 
 to the humble town of Penzance, Mr. Tonkin said 
 he thought Humphry might, with industry and 
 prudence, some day attain a reputable position 
 in the neighbourhood ;* adding, that he should 
 consider himself well rewarded for the care and 
 
 * When Davy was offered the appointment of Superintendant 
 of the Pneumatic Institution at Bristol, u he accepted it,” says 
 his brother, “ with the consent of all his friends, excepting Mr. 
 John Tonkin, who had hoped he would have settled at Penzance ; 
 and who,” Dr. Davy tells us in another place, “ was so angry with 
 Humphry for accepting the appointment, that he made some 
 alteration in his will in consequence.” Dr. Paris’s version of the 
 affair is as follows : “ His old and valued friend, Mr. Tonkin, 
 not only expressed his disapprobation of the scheme, but was so 
 vexed and irritated at having Ms favourite plan affixing Davy in 
 Ms native town as a surgeon thus thwarted, that he actually 
 altered his will, and revoked the legacy of his house, which he 
 had previously bequeathed him. Mr. Tonkin died on the 24th 
 December, 1801 ; so that, although he lived long enough to wit- 
 ness Davy’s appointment to the Royal Institution, he could never 
 have anticipated the elevation to which his genius and talents ulti • 
 mately raised Mm .” — Life of Sir Humphry Davy , p. 39- 
 
THE FIRST DRINK AT THE WELL. 
 
 57 
 
 affection he had bestowed upon Humphry if he 
 should live to see him settled as a surgeon in his 
 native town. 
 
 It was a lovely autumn evening, — such an even- 
 ing as, at the decline of the year, is known only in 
 those parts of our island which, from the mildness 
 of their climate, have been styled “ the Florence of 
 the North.” Mr. Tonkin and Humphry had strolled 
 out by Marazion towards St. Michael’s Mount, 
 journeying along the curved shore of the magnifi- 
 cent bay, with the ocean spread out on one side, in 
 a broad expanse of unsullied azure, and fringed 
 with a thin border of silver foam, as the waves 
 came rippling lazily over the yellow sands. As 
 they sauntered along, the breeze at sundown began 
 to set from the land towards the ocean, and, sweep- 
 ing across the warm earth, it came laden with the 
 perfumes of the many exotics that bloom in the 
 open air in that part of the world — the garden of 
 England ; for it was just the hour when the flowers 
 love to pour their odours into the lightened air, 
 like incense from a thousand chalices. The rays 
 of the declining sun gave a faint tint of purple to 
 the atmosphere, and the green sward, that was still 
 lustrous with the slanting light, was striped, here 
 and there, with the long shadows that streamed 
 from every object intercepting the beams ; while 
 the outlines of each form were growing more and 
 
53 
 
 THE WONDERS OF SCIENCE. 
 
 more definite, and the sides and peaks of the rocks 
 glittered towards the west, as if they were blazoned 
 with red gold. The brown cattle were quiet in the 
 fields, and the tranquil flocks on the distant hill- 
 sides rested there like clouds ; the branches of the 
 trees beside the roadway were shaggy, almost to 
 the tops, with the long stalks of wheat that dangled 
 from the twigs, telling of some high-laden harvest- 
 waggon that had lately swept by them. The white- 
 bellied swallows skimmed low over the earth in 
 zigzag lines, twittering as they went ; and there 
 was a soothing stillness all around that bathed the 
 soul in balmy quietude. 
 
 Towards the sea the scene was no less beautiful. 
 The ocean was like a huge green gem, and here 
 and there on its surface tiny boats seemed to revel 
 in the sundown breeze, now that it had sprung up, 
 and leant over on one side, as they went plough- 
 ing through the liquid field, turning up the white 
 surf on their way, and leaving far behind them 
 a long trail, that looked in the distance like a 
 seam upon the water ; while in the offing tall ships 
 stood against the sky, with their sails pouting and 
 shining white in the sun, like a pigeon’s breast. 
 Nearer the shore rose the majestic rocky mount of 
 St. Michael, towering above the sea like one of 
 Nature’s pyramids, with the broken outline of its 
 ivied sides showing sharp and clear against the 
 grey, aerial distance ; one half of it, towards the 
 
THE FIRST DRINK AT THE WELL. 
 
 59 
 
 east, was dusked in deep rich shadow, while the 
 other, towards the west, was bathed in such a 
 glory of ruby light, that the Mount shone as if it 
 had been one huge carbuncle studding the bright 
 shield of the ocean. Then, in the far west, the sky 
 and the sea were as a sheet of molten gold ; and, 
 almost resting on the ring of the horizon, was seen 
 the round, liquid orb of the sun, trembling like a 
 well of light, with the broad beams streaming up- 
 wards from it, and tinting the distant masses of 
 cloud, now ruby and now purple, till they looked 
 like islands of garnet and amethyst in the heavens. 
 
 It was low water, and the couple crossed by the 
 sands from Marazion to the Mount ; and here, after 
 passing the little cluster of fishermen’s houses that 
 skirted the base of the rocky pyramid, and mount- 
 ing a short distance up the cliff, they sat for a while 
 enjoying and discoursing of the many beauties of 
 the majestic scene that encompassed them on every 
 side. 
 
 And the prospect thence was indeed of the 
 grandest character. The shore stretched away, 
 revealing headland after headland, to where the 
 Lizard shot out far into the wave, the rocks there 
 seeming almost phosphorescent in the sun. Then 
 appeared St. Clement’s Island and the coast to- 
 wards the Land’s End, forming a shorter cape, and 
 completing the horn of the crescent of land towards 
 the west, that looked, as the waves grew crimson 
 
60 
 
 THE WONDERS OF SCIENCE. 
 
 in the sunset, as if bathed in a sea of wine. The 
 ocean here wore its most imposing attribute of un- 
 controllable immensity; for the Atlantic, across the 
 Bay of Biscay to the most western land of Spain, 
 lay on the south, and melted into distance there ; 
 while, beyond the extremity of our own island, no 
 shore intervened on the north between the line of 
 the horizon and the land of the New World. 
 
 It was a sight that Humphry loved as deeply as 
 old Mr. Tonkin to look upon, and the couple sat for 
 some time silently watching both the seas rolling 
 there towards the far distant Spanish and American 
 shores. 
 
 The boy, however, less capable of continuous 
 attention to the same subject, got to weary of the 
 scene sooner than the old man; and when Mr. Ton- 
 kin noticed Humphry’s admiration begin to flag, he 
 availed himself of the quietude of the time and 
 place to incite a taste in the lad for the profession 
 he wished him to follow. 
 
 Presently the old doctor caught sight of one of 
 the little transparent zoophytes that had been left 
 on the rocks by the receding tide. In size it was 
 not larger than a bird’s egg, of a globular form, 
 with several transparent ridges ranged along it, from 
 pole to pole, as it were, and it was nearly as pellucid 
 as the purest rock-crystal. 
 
 “ Look, my boy,” said Mr. Tonkin, turning to 
 Humphry, and pointing to the little ball of jelly at 
 
TIIE FIRST DRINK AT TIIE WEI.L 
 
 Page CO. 
 
THE FIRST DRINK AT THE WELL. 
 
 61 
 
 his feet; “here is an orb almost as wonderful as the 
 sun we have been lately gazing at. It gives light, 
 too, like it ; and though it looks there as if it were 
 only a few drops of the ocean gelatinised, it is 
 quickened with life, and performs motions that our 
 wisest engineers can but clumsily imitate.” 
 
 The eager boy was about to seize the wonder, so 
 that he might examine it more minutely. 
 
 “ Nay, if you touch it,” cried the old man, hastily, 
 as he grasped the youth’s arm, and held him back, 
 “ it will immediately dissolve, — thaw, as it were, to 
 death — so frail is its life, and nothing but a little pool 
 of water will remain of a creature that once could 
 make the sea glow with its fire. These little things 
 are by some styled the ‘ lucid gems of the waters.’ 
 By daylight, when in the ocean, they are visible only 
 by the bright rainbow hues that mark their path as 
 they paddle along ; but by night, Humphry, they 
 blaze with phosphorescent fire, so that some have 
 termed them 6 the stars of the sea.’ In warm and 
 calm evenings they often look like balls of light 
 rolling on the surface of the water, and the more 
 rapid their motion the more intense is the glow they 
 emit. Those eight transparent ridges you see there,” 
 continued the doctor, as he pointed with his cane to 
 the tiny watery globe, “ support as many rows of 
 broad, pellucid paddles, and these are all instinct 
 with life, and by their rapid motion cause the 
 animal to glide, meteor-like, through the waves. We 
 
62 
 
 THE WONDERS OF SCIENCE. 
 
 wonder at the recent invention of the steam-boat, 
 and speak with pride of the paddle-wheels with 
 which we are to walk upon the waters ; but the tiny 
 paddles here, boy, are far more perfect than any 
 ever contrived by human ingenuity, for in that little 
 aqueous ball the cumbrous machinery which is re- 
 quired to move our vessels along, is not needed, since 
 each float, self-moving without even a visible muscle 
 or nerve to stir it, keeps time with all the rest.” * 
 
 “ What wonder,” cried the poetic boy, “ is here 
 packed in a little living crystal, as it were, that can 
 make fire flash from what looks almost like a globe 
 of water, and that can perform the most rapid mo- 
 tions without, as you say, Mr. Tonkin, any visible 
 means of movement ! ” 
 
 “ Yes, indeed, my lad,” went on the old man ; 
 “there is a large store of marvels locked in that 
 little glassy casket. How does it get its food ? 
 How digest it ? and how is its frail body nou- 
 rished ? for we can trace no blood - vessels, nor 
 heart, nor glands — indeed, hardly any organs at 
 all — in the little clot of half-liquid life. All we 
 know, is, that it is furnished underneath with so 
 many tentacles or filaments, that serve it for claws, 
 and that these, which are set round an aperture that 
 we call a mouth, draw the food it lives upon into its 
 
 * The little zoophyte here described is a kind of small “ jelly- 
 fish” known by the name of the “ Beroe.” It may be often seen 
 on our shores. 
 
THE FIRST DRINK AT THE WELL. 
 
 63 
 
 body — which is literally nothing but a stomach. If 
 we were to watch long enough, we should see the 
 food thus seized and swallowed gradually dissolve 
 and be reduced to a fluid state, while the more 
 solid and indigestible portion would be rejected 
 by the aperture through which it entered. The 
 nutritive matter we know to be absorbed by the 
 walls of the stomach, every part of which ap- 
 pears to be endowed with equal power in this 
 respect; and it is then conveyed to the remoter por- 
 tion of the body by the simple imbibition of one 
 part from another, without any proper circulation 
 through vessels. In some animals of this class the 
 external covering of the body and the lining of the 
 stomach so closely correspond in their structure as 
 to admit of being changed one for the other — for 
 the animal may be turned inside out without its 
 functions being in any way deranged.” 
 
 “ Can it be ?” said Humphry, filled with delight. 
 “ Where can I learn these things, sir ? Why was I 
 not taught them at school ? ” 
 
 “ You shall learn them, my boy,” replied the old 
 man, pressing the lad’s hand with pleasure to find 
 the taste that he had longed to develope for his own 
 favourite study springing up in Humphry’s mind. 
 “ And think, if that little lump of jelly — which is, 
 perhaps, the simplest form of life, where the vital 
 mechanism is seen in its rudest form — can stir you 
 to so much wonder, — think, I say, Humphry, what 
 
84 
 
 THE WONDERS OF SCIENCE. 
 
 admiration will be excited in you when you come to 
 comprehend the beautiful processes and organism 
 exhibited in complicate animals like ourselves ! If 
 a living, digesting creature — a thing almost without 
 sense — a mere moving mouth — can appear so won- 
 derful to you in its structure, what marvels shall 
 you not find in the constitution of a thinking, 
 speaking, reasoning being like man!” 
 
 Then the old doctor ran over to the youth the 
 many sources of knoivledge that the study of hu- 
 man life opens up to the thoughtful and inquiring 
 mind. 
 
 He told the eager boy — as they sat there in the 
 subdued light of the evening, with the hum of the 
 sea that rippled into the caverns at the base of the 
 Mount, falling almost musically on the ear — how, in 
 the organism of the nerves and brain, we get our 
 first insight, rude though it be, into the subtle 
 processes of the senses, and even the mind itself. 
 He told him, also, how, in the senses themselves, lay 
 the rudiments of all the sciences ; how, without the 
 sense of vision, there could have been no “ optics, 
 and consequently no astronomy — for to the blind the 
 movements of the planet's, and even the very exist- 
 ence of the stars, must, of course, have remained 
 unknown : in like manner, without the sense of 
 hearing there could have been no “acoustics” and 
 no music ; and without the sense of muscular effort 
 no knowledge of weight, and consequently of “ gra- 
 
THE FIRST DRINK AT THE WELL. 
 
 65 
 
 vitation ” — the main-spring, as it were, of the me- 
 chanism of the universe. 
 
 Mr. Tonkin explained to the youth, moreover, that 
 had we been formed without the exquisite organ of 
 the hand there would have been little work done, 
 and but little art achieved ; and without the organs 
 of the mouth, there could have been no inter-com- 
 munication of thought — no transfusion of mind into 
 mind, by which one wise man now-a-days contains 
 stored in his own brain the wisdom of almost all 
 those who have preceded him. And further, if we 
 had had no appetites, and no pains nor uneasinesses 
 to stir us to action, we should, even with the beau- 
 tiful muscular apparatus with which our frames 
 are fitted, have remained idle and inactive all our 
 time, starving to death with delight. 
 
 “ Some persons,” said Mr. Tonkin, “ have sup- 
 posed that plants may be susceptible of feeling, as 
 well as ourselves and the rest of the animal race. 
 But that trees and herbs are incapable of knowing 
 either pain or pleasure ” (he added) “ is made evi- 
 dent, physiologically, by the fact that they are sup- 
 plied with no organs of locomotion, and conse- 
 quently deprived of the means of avoiding the one 
 and seeking the other. For, so benevolently is the 
 world arranged, that wherever feeling is given, the 
 power of acting is immediately associated with it , 
 indeed, it requires hardly a moment’s thought to 
 perceive that it would have been incompatible with 
 
 F 
 
66 
 
 THE WONDERS OF SCIENCE. 
 
 All-Kindness to have made creatures sensible to 
 pain, and yet have denied them the means of escape 
 from it.” 
 
 After this the old man pointed out to Humphry, 
 that in the comparison of one system of life with 
 another, and so tracing the delicately interwoven 
 chain of animal creation, we perceive that the first 
 type of sentient existence was a mere stomach — a life 
 of pure appetite — susceptible of no other feeling than 
 hunger, and fitted only with organs for seizing and 
 assimilating its food ; while as we advance gradu- 
 ally in the scale of development, we find nerve after 
 nerve added, and a new set of feelings and actions 
 brought out, with each new set of fibres. “We dis- 
 cover, besides,” he continued, “ that when a little 
 kernel of nervous matter was superadded to the 
 previous sentient apparatus, the wondrous sense of 
 vision was first awakened in animal life, and how 
 the addition of another such little kernel made an 
 animal for the first time hear, and another gave 
 the first sense of odour to the world, while another 
 added taste to the food and drink.” 
 
 And when he had thus briefly explained to the 
 youth the uses and characteristics of. the several 
 organs in man and the lower animals, the old 
 gentleman went on to point out to him how these 
 same organs were nourished, and the destruction 
 that was continually going on in the body — 
 “ for,” said he, “ we cannot move a muscle, not even 
 
THE FIRST DRINK AT THE WELL. 
 
 67 
 
 wink our eyelids, without wasting some tissue or 
 other” — was being as continually repaired by the 
 food consumed. Pursuing this subject, he then 
 proceeded to explain to young Humphry how the 
 blood was made to circulate by means of the cun- 
 ningly-wrought chambers of the heart through the 
 veins and arteries, distributing health and vigour 
 to the different organs in its course — now reno- 
 vating the tissues, now depositing little specks of 
 bone, then extending the filaments of hair, and 
 then exciting thought and developing feeling in 
 the nerves and brain, stimulating action in the 
 muscles, and diffusing warmth throughout the 
 whole frame, — all these different functions being 
 performed by the one wondrous substance in which, 
 even when examined by the highest microscopic 
 power, it was impossible to detect even the rudi- 
 ments of the many various tissues it formed. 
 
 “ Such,” said Mr. Tonkin, 66 is a part of the mar- 
 vellous process of secretion, — a process so subtle that 
 even the wisest can only wonder in their ignorance 
 concerning the function ; for it is a mystery to them 
 how, by means merely of little glands, so many 
 different things can be produced from one and the 
 same fluid. How, for instance, skin, cartilages, 
 muscles, hair, nails, bones, tears, and the infinite 
 variety of products which our bodies are made up 
 of and evolve, can all come from the same ruby 
 stream, and that a small nut-like organ only shall 
 
68 
 
 THE WONDEKS OF SCIENCE. 
 
 be necessary to eliminate each different substance 
 from it. Then, again, there is the beautiful pro- 
 cess of breathing, by which the vital air is com- 
 bined with the blood, and the blue fluid of the veins 
 changed into the crimson stream of the arteries 
 and he recounted to him the while how respiration 
 among animals was merely a process of burning, 
 accompanied with the evolution at each exhalation 
 of so much invisible smoke from the lungs — the same 
 smoke, indeed, as comes from burning charcoal : 
 and he told Humphry that he would one day come 
 to see how the rotting wood underwent precisely 
 the same chemical change as the breathing man, 
 and that what is a process of death and decay in 
 the one is a process of life and health in the other. 
 
 “ Indeed,” concluded the old gentleman, “there is, 
 perhaps, no sphere of knowledge so replete with 
 wonder and beauty as that which unfolds to us the 
 mysteries of our own existence — no science which 
 gives us greater wisdom or deeper insight into the 
 constitution of our natures, as well as that of the 
 elements around us. To comprehend such a sub- 
 ject, even vaguely, requires an intimacy with almost 
 every branch of learning, dealing as it does at 
 once with the material and spiritual ; while a j ust 
 appreciation of the wonders it reveals cannot fail to 
 inspire us with the highest regard for life, even in 
 its rudest forms, and render us more keenly alive - 
 to suffering than the rest of humanity, from the 
 
THE FIRST DRINK AT THE WELL. 
 
 69 
 
 greater sense it gives us of the causes of pain, 
 while it arms us, at the same time, with the means 
 of relieving anguish, restoring health, and often of 
 prolonging existence. 
 
 “ Some there are,” he added, “ who prefer poetry 
 to philosophy; but science, Humphry, rightly under- 
 stood, is merely the translation of the Great Poem 
 of Nature — that which the Almighty himself con- 
 ceived when he designed Creation. There may be 
 high beauty in music, boy ; but, to my mind, there 
 is even higher beauty still in comprehending the phe- 
 nomena by which the Creator has fitted us to enjoy 
 it. In the rich glories of colour there is, certainly, 
 an exquisite feast of visual delight; but what array 
 of tints, be they ever so beautifully blended — what 
 tracery of form, be it ever so cunningly put toge- 
 ther — can fill the mind with ecstasy equal to the 
 contemplation of that splendid little translucent 
 globe, the eye— a crystal world in itself, filled with 
 an infinity of wonders — by which we are enabled to 
 perceive the light, and to tell one hue from another? 
 What work of art, however consummate the execu- 
 tion — what picture, however choice the painting or 
 grand the composition — what architecture, however 
 commanding the mass or harmonious the details — 
 and what poem, even though the verse be melli- 
 fluent as music on the water, though the imagery 
 be luminous and profuse as the stars in winter, and 
 the thoughts subtle as the mountain air, can bear 
 
70 
 
 THE WONDERS OF SCIENCE. 
 
 the least comparison, either as regards the skill of its 
 art, the craft of its design, or the nice adjustment of 
 its parts, with the organism of the smallest ani- 
 malcule fashioned by the Great Artist, Architect, 
 and Poet of All?” 
 
 The sentence was barely finished when the sharp 
 report of a gun rattled amidst the rocks, and Hum- 
 phry, whose eyes had been turned upward as he 
 listened to the wonders recounted by the doctor, 
 saw the gull, which but a moment before he had 
 noticed almost lying on the air, poised on its white 
 outstretched wings, bound suddenly upwards with 
 a shriek, and the instant afterwards it tumbled 
 heavily on the crag at Mr. Tonkin’s side. 
 
 The old gentleman stretched out his hand and 
 grasped the still warm and quivering form of the 
 bird. “ If the wings of this body had been moved 
 by some piece of curious mechanism, Humphry,” he 
 said, — “if by some cunning combination of cog- 
 wheels, and levers, and springs, it had been made to 
 beat the air and to rise by clock-work into the sky, 
 how would men have prized the marvellous appa- 
 ratus ! Monarchs would have given immense wealth 
 to possess it: and yet the machine would have been, at 
 best, but a clumsy toy compared with the exquisite 
 arrangement here ; for in this wonderful piece of 
 divine mechanism the force was supplied by means 
 of little threads of nerves that the unaided eye can 
 scarcely trace — the movement given by muscles so 
 
TIIE FIRST DRINK AT THE WELL. 
 
 71 
 
 beautifully elastic that no artificial fabric can imi- 
 tate their play — and the bones jointed together so 
 aptly, that when our wisest engineers wish to get 
 movements in all directions, they can only copy 
 their arrangement, instead of designing any such 
 hinges for themselves. Then, again, to give light- 
 ness to the whole, these same bones were filled with 
 air, and the living, flying machine, so made more 
 buoyant in the thin fluid in which it was destined 
 to soar. But let us suppose, Humphry, that it might 
 be within the compass of art to reproduce such an 
 apparatus as this by mechanical means ; still what 
 mechanism, however skilful, could have supplied the 
 wonderful motive power that lately quickened it ? 
 What spring, or arrangement of weights, could imi- 
 tate the action of life ? Could steam even, or electri- 
 city itself, have moved the wings and guided them, 
 like the subtle principle that stirred and directed 
 this body only a few moments past ? And then, what 
 cunning engineery could ever have performed the 
 function of the senses ? Could mechanism have 
 made the animal see ? Could the galvanic fluid— 
 the most spiritual, perhaps, of all our motive powers 
 — have made it love its young, or know when to 
 repair its strength with food ? Ah ! had the thought- 
 less fool who, for wanton sport, Humphry,— who 
 for the mere sake of hitting a moving mark in the 
 air — known and pondered over all this, do you 
 not think he would have found more pleasure 
 
72 
 
 THE WONDERS OF SCIENCE. 
 
 in watching the performance of all its wondrous 
 functions than in destroying the beautiful principle 
 which animated them ? Had he needed its body for 
 food, hunger would have excused him. But no ! It 
 was simply the petty pleasure — the little spasm of 
 exultation — that we derive from success in trials of 
 skill which led him to put an end to the life of the 
 poor bird, that had surely as much divine right to 
 its place in creation as even a king himself. 9 ’ 
 
 Humphry was overjoyed with the lesson of kind- 
 ness and wisdom he had learnt. He had been so en- 
 raptured with the knowledge that Mr. Tonkin had 
 poured into his mind that he sat almost like one 
 entranced, with his spirit lulled in a dream of bright 
 things he had never heard or thought of before. 
 
 The boy till now had been more smitten with the 
 beauty of creation than curious as to its mysteries. 
 True, in his romantic visits to the extremity of the 
 island, as well as to the Mount of St. Michael, he 
 had been often led to wonder how the huge masses 
 of rock had come there ; and he had many times 
 pondered over the origin of metals, as in his ram- 
 bles he had passed the openings of the mines that 
 perforated the surface of his native country, wonder- 
 ing as he went along why a vein of one ore should 
 be deposited here, and another there. As he no- 
 ticed, too, the Atlantic waves lashing the Land’s 
 End, he would repeatedly question himself as to 
 
THE FIRST DRINK AT THE WELL. 
 
 73 
 
 what became of the rocks that the sea was for ever 
 crumbling into sand ; and he would form fanciful 
 theories in his own mind, as to how the detritus of 
 one ancient country became at last the substratum 
 of some new one. Again, the ebbing and flowing 
 of the ocean had led his mind to ruminate vaguely 
 upon the mighty pulsation of the tides, while the 
 sight of the liquid orb of the sun sinking below the 
 ring of the horizon, away towards the invisible 
 shores of America, had often turned his thoughts 
 to the revolutions of the planets, and set him rudely 
 speculating as to the source of the light and the 
 heat of the sun itself. 
 
 Still the youth as yet had found more pleasure 
 in contemplating the golden glories of sunset, than 
 in seeking to comprehend the wisdom that de- 
 signed them. The sea, too, to him had been more 
 an object of grandeur than a stimulus to thought, 
 while the sight of the rocks had filled his mind 
 with admiration far oftener than they had quick- 
 ened it with inquiry. The mystery, and even the 
 beauty, of the principle of life, however, had never 
 before been heeded by Humphry; so that, when he 
 heard Mr. Tonkin relate the many wonders wrought 
 in the changes that were continually going on in his 
 own frame, the boy was almost overwhelmed with 
 the flood of new thoughts that poured through his 
 brain, and he felt as if he could have sat and 
 listened to the old man the long night through. 
 
74 
 
 THE WONDERS OF SCIENCE. 
 
 Accordingly, when Mr. Tonkin came to a con- 
 clusion, Humphry begged him to proceed, saying 
 he had begotten emotions in him that he had never 
 known before ; and he felt as if a burning thirst had 
 come upon him for the truth, and he could drink of 
 such knowledge for ever without quenching it. 
 
 Mr. Tonkin was pleased to find he had stirred 
 the boy’s thoughts so effectively ; and he promised 
 him that, before long, he would place him in a 
 position where he should be able to pursue the 
 subject as far as his powers could carry him. 
 
 Not many weeks after the above conversation, 
 Humphry, to his exceeding delight, was articled to 
 Mr. Bingham Borlase, the surgeon and apothecary 
 of Penzance ; and there, alone in his little chamber, 
 at night, he wrote the following passage in his 
 note-book 
 
 “ I have neither riches nor birth to recommend 
 me; yet, if I live, I trust I shall not be of less 
 service to mankind and to my friends than if I 
 had been born with these advantages.”* 
 
 * This memorable passage was written in a diary kept by 
 Humphry Davy during his youth. His brother, after quoting it, 
 adds, “and this early sentiment never forsook him; even in his 
 last days he had a feeling of the same kind, looking forward, 
 were his life spared, to greater exertions.” 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 75 
 
 CHAPTER Y. 
 
 THE FIRST GLIMMER OF THE SAFETY-LAMP. 
 
 Humphry was hardly at home in his new quarters, 
 when an incident occurred that directed his mind 
 towards the investigation of one of the most subtle 
 and mysterious principles in nature. 
 
 Mr. Borlase had returned from his day’s rounds, 
 and as he was busy unfastening the long leggings 
 that covered his black silk stockings, he informed 
 the family, who, with the boy, were gathered round 
 the tea-table in the little parlour adjoining the 
 shop, that he had heard that day of a fearful 
 explosion which had occurred, during the last 
 month, in one of the Welsh coal-mines. 
 
 “ It seems,” said the doctor, as he took his place 
 at the table, “ that there were two ‘ shifts,’ or sets, 
 of men employed at the pit. The first went to work 
 at four in the morning, and were relieved by the 
 next set at eleven ; and so secure was the mine con- 
 sidered — so little thought of danger, indeed, entered 
 the minds of the pitmen — that the second shift of 
 
76 
 
 THE WONDERS OF SCIENCE. 
 
 men often entered tlie mine before the first had 
 left it. This happened to be the case, they tel] 
 me, at the time of the accident; for shortly after 
 the second set of hands had descended the shaft, 
 the people above-ground were alarmed by a terrible 
 report, followed by others so quickly, that it sounded 
 like the firing of infantry, and a sheet of flame was 
 seen to flash from the mouth of one of the shafts. 
 The ground shook as if with an earthquake, the 
 tremor being felt for half-a-mile round the work- 
 ings ; while the dull, subterranean boom of the ex- 
 plosion was heard, they say, nearly four miles off. 
 Yast clouds of dust rose high in the air, in the 
 form of an inverted cone, and large masses of 
 timber and fragments of coal were shot straight 
 up from the pit-mouth, as from a huge piece of 
 artillery, and fell with a heavy crash near it ; 
 while the dust, borne by the wind, descended in a 
 shower upwards of a mile from the spot, and as it 
 did so, it caused a gloom, I am assured, like early 
 twilight, in the neighbouring villages, inhabited 
 chiefly by the families of the miners. 
 
 “ The boom was no sooner heard,” continued 
 Mr. Borlase, “the tremor of the earth felt, and 
 the darkness from the shower of ashes perceived, 
 than the wives and children of the miners rushed 
 frantically towards the pit. Horror and dismay 
 were painted on every face. The crowd thickened 
 from all sides, so that in a short time several hun- 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 77 
 
 dreds of women and children were gathered round 
 the shaft. The air, the people say, resounded with 
 shrieks and cries of despair for the fate of husbands, 
 fathers, and sons, from many a bursting heart. 
 
 “ The machinery, it was then found, had been 
 rendered useless by the explosion, so that it was 
 near upon an hour before thirty-two persons — all 
 that survived the dreadful catastrophe — had been 
 brought to daylight, and of these twenty-nine only 
 lived to relate what had occurred in the mine 
 below. 
 
 “ It was now discovered that one hundred and 
 twenty-one, men and boys, had been in the pit when 
 the accident happened, so that eighty-nine poor souls 
 still remained entombed in the workings. Those 
 who had their friends restored to them appeared, 
 it is said, to suffer for a while as much from an 
 excess of joy as they had, a short time before, from 
 the depth of despair ; while those who were yet in 
 the agony of suspense filled the air with shrieks 
 and howlings, and ran about wringing their hands 
 and throwing their bodies into the most frantic and 
 extravagant gestures. 
 
 “ After some little time, it appears that nine 
 persons volunteered to descend into the pit, with 
 the faint hope that some engulfed below might 
 still survive. As the fire-damp, however, would 
 have been instantly ignited by candles, those who 
 went to search the mine lighted their way by c steel- 
 
78 
 
 THE WONDERS OF SCIENCE, 
 
 mills,’ as they are called, which,” added Mr. Bor- 
 lase, turning round to Humphry, “ are small 
 machines for giving light, by turning a cylinder 
 of steel against a piece of flint ; for it has been 
 found, I should tell you, that though the fire-damp 
 is immediately ignited by flame, it is not explosible 
 by sparks.” 
 
 The remark evidently sank deep into the boy’s 
 mind, for he knit his brows and bit his lips as if a 
 sudden thought had flashed across his brain. But 
 Humphry was too much interested in the narrative 
 to interrupt the doctor, so he said not a word, and 
 waited anxiously for Mr. Borlase to proceed. 
 
 “ The men who had descended the pit,” continued 
 that gentleman, “ attempted to make their way to- 
 wards the spot where they knew the miners must 
 have been at the time when the explosion happened. 
 Their progress, however, was soon intercepted by 
 the prevalence of what is called the 4 choke-damp,’ 
 — an atmosphere which it is suffocation to inhale, — 
 and the sparks from the steel -mill, they say, fell 
 into this like dark drops of blood. 
 
 “ Deprived of light, therefore, and nearly stifled, 
 they were forced to grope their way back to the shaft. 
 
 “ As each came up he was surrounded by a group 
 of anxious inquirers, but not a ray of hope could be 
 elicited. It was impossible, they told the' people, 
 for any breathing thing to live in the mine. At - 
 first, the assertion seemed to obtain some credit, 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 79 
 
 but hope still lingered. All there recollected how 
 persons had survived similar accidents, and stories 
 were told how, upon opening a mine forty days 
 after an explosion, men had been found still alive, 
 having subsisted during the time on horse-beans 
 and candle-ends. Then distrust began to enter the 
 minds of the crowd, and some suggested that want 
 of courage or bribery had induced the men who had 
 descended to magnify the danger ; so that when it 
 was proposed by the owners to close the mouth of 
 the pit, and so shut out the air from it — for the most 
 experienced ‘viewers’ had pronounced the mine to 
 be on fire — the proposition was received with cries 
 of ‘Murder !’ and with expressions of determination 
 to oppose such a proceeding with violence ! 
 
 “ All that night, they tell me,” the doctor pro- 
 ceeded, “ many of the widows lingered about the 
 mouth of the pit, with the hope of hearing the cries 
 of a husband or a son. 
 
 “ The next morning it was again proposed to 
 exclude the air; still the populace, made furious by 
 their misery, would not allow the project to be 
 carried out until some others had again descended 
 the shaft. But none could now be found hardy 
 enough to enter the jaws of the burning cavern. 
 At length, however, two brave fellows were induced 
 to make the perilous attempt, and they nearly lost 
 their lives in so doing. 
 
 “ The account given by these adventurers (for 
 
80 
 
 THE WONDERS OF SCIENCE. 
 
 they confirmed the opinion as to the pit being on 
 fire) ultimately convinced the people of the impos- 
 sibility of their friends surviving in so deadly an 
 atmosphere, and reconciled them to the plan of ex- 
 cluding the air. Accordingly the shaft was closed, 
 with the eighty-nine poor souls entombed in it, and 
 more than a month elapsed before the mine was 
 opened again and in a state to admit of an examin- 
 ation. 
 
 “ During this interval, I leave you to imagine,” 
 went on the apothecary, “what must have been the 
 terrible suspense of those whose love made it impos- 
 sible to eradicate all hope from their bosoms. The 
 widows, anxious to believe that their husbands still 
 lived in the closed mine, gave a ready credence to 
 the idle tales of escape that were continually being 
 circulated through the country. These inventions, 
 however, had the effect of daily harrowing up afresh 
 the sorrows of the people ; so that when the morn- 
 ing came that had been appointed for the re-opening 
 of the pit, the distress of the neighbourhood burst 
 forth once more with almost redoubled fury. 
 
 . “ A great concourse of people assembled round the 
 mine on that sad day : some came out of curiosity, 
 others out of public sympathy, but the greater part 
 came there with broken hearts and streaming eyes, 
 intent on once more beholding the loved form of a 
 father, brother, husband, or son. 
 
 “ Soon a message was despatched for a number 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 81 
 
 of coffins to be in readiness at the pit-mouth. Up- 
 wards of eighty of these had been ready prepared, 
 and they had to pass by the miners’ villages on 
 their way to the shaft. As soon as a cart-load of 
 them was seen, the howling of the women, who had 
 not yet found their way to the melancholy spot, 
 floated on the breeze in low, fitful gusts, presaging a 
 scene of the greatest distraction and confusion ; and 
 as each load of coffins came to the pit, it brought a 
 long train of wretched mourners in its wake. 
 
 “ The bodies of the ill-fated men were found 
 under various circumstances. One, from his posi- 
 tion, must have been asleep when the explosion 
 happened ; others were huddled together in ghastly 
 confusion — twenty-one were found in a heap in one 
 spot. The power of fire was visible upon all: 
 some were scorched ; others almost torn to pieces ; 
 while others, again, appeared as if they had been 
 stifled at their work. 
 
 “ Then came the heartrending scene,” added 
 Mr. Borlase, “ of mothers and widows examining 
 the mangled remains for marks by which to identify 
 the bodies of their lost sons and husbands. Few, 
 however, were able to recognise their relatives by 
 their features; their clothes, their shoes, and — 
 when these were too much burnt to be known again 
 —their tobacco-boxes, or some token of affection, 
 were often the only indications by which the lost 
 friend could be singled out from the rest. 
 
 G 
 
82 
 
 THE WONDERS OF SCIENCE. 
 
 “ Every family had made some arrangements for 
 receiving the dead bodies of their kindred, but the 
 doctor had very properly stated that, in his opinion, 
 such a proceeding might spread a putrid fever 
 through the neighbourhood, and the first body, 
 when exposed to observation, presented so horrible 
 and corrupt an appearance, that the people were 
 induced to consent that each corpse should be in- 
 terred as soon as it was discovered — on condition 
 that the hearse, in its way to the chapel-yard, 
 should pass by the door of the deceased. 
 
 “ And the condition was duly complied with,” 
 concluded the doctor, solemnly. “ Hour after hour, 
 and day after day — for the finding and removal of 
 the bodies continued for upwards of a week — the 
 funeral carriage might be seen slowly wending its 
 way through the half-desolate miners’ villages, 
 passing first by the door of one closed cottage, 
 and then by another, while at the hatches of the 
 others stood groups of women, the greater part of 
 whom were habited in black, with little things by 
 their side, and some with infants in their arms, 
 mostly wearing some humble mark of mourning. 
 As the hearse moved on, the women, with tears in 
 their eyes, would tell one another whose body was 
 then on its way to its last home, and each would 
 have some little story to recite of good done and 
 charity bestowed by the ill-fated man, while all 
 would sigh to think what would become of the 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 83 
 
 wretched widows iand little orphans who, as the 
 bier stopped at the cottage, might be seen, with 
 streaming eyes and dejected heads, to issue forth 
 and follow the funeral carriage slowly and sadly 
 to the grave. 
 
 “ For ten long, melancholy days,” said Mr. Bor- 
 lase, mournfully, “ were the shutters of the houses 
 closed in the miners’ villages, and for ten days did 
 the bell of the neighbouring chapel continually toll 
 — for the finding of the bodies lasted all that time: 
 and by this one terrible accident there were no less 
 than ninety-two pitmen hurled into eternity, while 
 as many as forty widows and one hundred and six 
 orphan children were deprived of their protectors 
 and ordinary means of subsistence.” * 
 
 Mr. Borlase, on finishing his melancholy story, 
 turned to Humphry, and saw the tears trickling 
 from his cheeks. 
 
 There was a silence among all present, as if the 
 awe of the calamity was still pressing on their 
 hearts. 
 
 Presently the impulsive boy started to his feet 
 
 * The details of this accident are taken from the account of an 
 explosion which occurred at Felling Colliery, near Sunderland, 
 on the 12th of May, 1812, and of which a narrative was prefixed 
 by the Rev. John Hodgson to the published form of the funeral 
 sermon he preached on the occasion. It was this fearful explo- 
 sion which led to the formation of the Society for the Prevention 
 of Accidents in Coal Mines ; and it was at the request of the 
 members of this body that Humphry Davy was induced to perfect 
 his safety -lamp. 
 
84 
 
 THE WONDERS OF SCIENCE. 
 
 and cried, “ I’ll put an end to this shocking misery, 
 please God I will, some day.” 
 
 The quick eye of young Humphry saw a smile 
 play faintly on the doctor’s lip, and he added, “ I 
 know, sir, you have reason to doubt my power to 
 do as I say, and, perhaps, it may take me years of 
 hard study to gain the knowledge to enable me to 
 compass my end ; but though it cost me a lifetime 
 I will master it at last. I have sufficient faith 
 in the goodness of the Creator, to believe that these 
 terrible afflictions come upon us only through our 
 ignorance, and that if we but study His will, 
 as expressed in the laws of the universe in which 
 He has placed us, He has given us the faculty to 
 avert misery, and to turn the current of Nature to 
 our own welfare rather than injury.” 
 
 Mrs. Foxell (Mr. Borlase’s sister), who was pre- 
 siding at the tea-table, and who had already learnt 
 to esteem Humphry highly for the generous qualities 
 of his nature, was moved almost to tears with the 
 benevolent impulses of the boy ; for she was natur- 
 ally of a kindly disposition, and the melancholy 
 details of the accident had so affected her, that 
 when she heard the youth vow he would one day 
 put an end to such calamities, the transport of 
 joy she felt was too much for her woman’s heart, 
 and though she would have cheered him on, there 
 was an hysteric spasm in her throat that prevented 
 her utterance for a time. 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 85 
 
 Presently , the lady said, “ Do not be discouraged 
 by what my brother may say to you, Humphry. 
 He has lived too long in the world to be as hope- 
 ful as_ you are, and he is so accustomed to scenes of 
 anguish that suffering is, with him, almost an every- 
 day occurrence. But you and I, boy, are, thank 
 Heaven, unused to such sights, so that the mere 
 recital of them stirs us to the depths of our natures. 
 Besides, it is only a woman who can fully compre- 
 hend the distress wrought by such a catastrophe as 
 my brother has recounted to us ; for the real suffer- 
 ing in all such cases falls lighter on those who are 
 even destroyed by it than it does upon those who 
 are left behind. It is not so much the dead husbands 
 I grieve for, as the living widows ; the lost fathers 
 felt but a momentary pang, but the fatherless child- 
 ren have years of misery to pass through : and it is 
 because my sex teaches me to understand these 
 things deeper than yours, that I, for the sake of the 
 poor living victims — the wives and babes, beggared 
 in heart as well as in means — would not have a 
 word said that would take away one spark of hope 
 from your noble purpose. Though the prospect of 
 success may appear barren to some minds, never- 
 theless if you, Humphry, can, in the ardour of your 
 sympathy, imagine such an object to be barely possible 
 of attainment, I say to you, Go on ; and God speed 
 you in your good work. You wish such a result 
 to be possible, and therefore believe it to be so, and 
 
86 
 
 THE WONDERS OF SCIENCE. 
 
 believing it, perhaps you may find it to be as you 
 fancy ; whereas if you had no faith in it you would 
 never work at it, and consequently could never 
 accomplish it. Think, too, if you should one day 
 gain your end, what honour would await you — how 
 many thousand poor creatures would hail you as 
 their preserver — what evils you would be the means 
 of preventing — ay, and even what wealth you might 
 reap from such a discovery, for you could secure it 
 to yourself, and so derive a large income from the 
 profits of it.” 
 
 “ No, my good madam,” replied Humphry, half 
 indignant at the idea of enriching himself by such 
 means, “ I would never think of such a thing. 
 My sole object would be to serve the cause of 
 humanity, and, if I succeeded, I should be amply 
 rewarded in the gratifying reflection of having done 
 so. All I desire is a competence, and this, I hope, 
 my profession will yield me ; more wealth might be 
 troublesome, and distract my attention from pursuits 
 in which, even now, I delight. Biches,” he added, 
 “ could not give me either fame or happiness ; 
 they might, undoubtedly, enable me to put four 
 horses to my carriage, but what would it avail me 
 to have it said that Humphry Davy drives his 
 carriage and four?”* 
 
 * The above generous sentiments are taken, almost verbatim, 
 from a letter of Mr. Buddie — “ a person,” says the biographer 
 of our hero, “ whose extensive practical knowledge justly entitled 
 him to be considered as the highest authority on all subjects con- 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 87 
 
 The noble disinterestedness of these sentiments 
 produced a deep impression upon all present, for 
 they were uttered, not in the same passionate tone 
 as that in which the boy had previously spoken, 
 but calmly and almost gravely, as if they were the 
 result of long reflection, and showed that the youth 
 had already learnt to prize fame more than wealth, 
 — that his mind was bent on winning an honourable 
 reputation rather than amassing a worldly fortune. 
 
 Old Mr. Borlase, the venerable father of Hum- 
 phry’s master, looked with wonder and admiration 
 at the youth, and drawing him closely to him, ex- 
 claimed, “ There’s a brave lad ! You remind me, 
 
 nected with the art of mining,” and who was of great service to 
 Davy in carrying out his invention of the safety-lamp. That 
 gentleman, writing to Dr. Paris, says, “ Sir Humphry Davy ac- 
 companied me into some of our fiery mines, to prove the efficacy 
 of his lamp. Nothing could be more gratifying than the result 
 of the experiments, as they inspired everybody with perfect confi- 
 dence in the security which his invention had afforded. Sir 
 Humphry was delighted, and I was overpowered with feelings of 
 gratitude to the great genius which had produced it. I felt, how- 
 ever,” continues Mr. Buddie, ** that he did not contemplate any 
 pecuniary reward, and in a private conversation I remonstrated 
 with him on the subject. I said, ‘ You might as well have secured 
 this invention by a patent, and received your five or ten thousand 
 a-year for it.’ The reply of this great and noble-minded man was, 
 i No, my good friend, I never thought of such a thing,’ ” &c. as 
 above given. “ I expostulated,” adds Mr. Buddie, “ saying, 
 that his ideas were much too philosophic and refined for the occa- 
 sion. He replied, ‘ I have enough for all my views and purposes ; 
 more wealth might be troublesome,’ ” and so on, the remainder 
 of the speech being nearly word for word with that w r hich young 
 Humphry has been here made to deliver. 
 
88 
 
 THE WONDERS OF SCIENCE. 
 
 Humphry, of my poor brother the clergyman, who 
 is dead and gone now, rest his soul ! — I mean him, 
 you know, that wrote the 6 History of Cornwall ; ’ 
 a wonderful book it is, too ! — he’d just the same 
 notions when he was a youngster, and used to say, 
 that money was only of value for the happiness it 
 could bring, and that there was more real pleasure 
 to be found in seeking and discovering the truth 
 than the richest fortune could purchase. I am 
 sure, for my part, lad, I hope you may succeed in 
 your noble object ; and I have seen quite enough 
 changes in my time to think nothing impossible 
 now. Why, I have heard my grandfather say that, 
 when he was a boy, coal itself was seldom used as 
 fuel, and now see what wonders are being worked 
 by it. Haven’t we just had one of those wonderful 
 steam-engines, which have been of late years in- 
 vented by Mr. Watt, put up at the Wherry Mine 
 close by?”* 
 
 The boy nodded quickly, as if he was well ac- 
 quainted with the locality. 
 
 “ And there,” continued the old gentleman, “ that 
 great monster of brass and iron goes on, day after day 
 
 * Watt’s first patent was in the year 1769, and that for his 
 double engine was in 1781. Dr. Davy, in speaking of the Wherry 
 Mine as being a place of favourite resort with his brother during 
 his youth, says, “ The steam-engine there (an invention,” he 
 adds, “ which had only a short time before been perfected by 
 Mr. Watt) was one of the earliest that had been introduced into 
 Cornwall.” 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 89 
 
 and night after night (though the shaft of the mine, 
 you know, is in the sea, and the workings entirely 
 underneath the sands), acting at a distance over the 
 surface of the ocean, and drawing up the water from 
 beneath its bed ; and all, too, by means of a few 
 bushel of coals. I am sure when I first saw the 
 engine lifting up its arms, and snorting away as if 
 with the heavy labour it was doing, it put me in mind 
 of the old fable, I learnt at school, of Prometheus, 
 who stole fire from the sun, you know, boy, and made 
 men with it out of the materials of the earth. For 
 it struck me as being a huge steam man — a kind of 
 monster labourer, as it were, that would work on 
 for ever, without needing any sleep, and without 
 knowing any fatigue ; and that wanted only coals, 
 instead of bread and meat, to keep it going. Ah ! 
 we live in wonderful times, my lad, that we do ; 
 and whatever the world will come to in a few years, 
 when I am dead and gone, is more than I can say. 
 Why, Mrs. Foxell here was reading to me the other 
 day, out of the ‘ Sherbourne Mercury,’ a paragraph, 
 saying, that a Mr. — Mr. — What was the name, my 
 dear ? ” 
 
 “ Symington,” answered the lady appealed to. 
 
 “Yes; that’s it! — Mr. Symington,” proceeded 
 the old gentleman, “ had been making some experi- 
 ments on the Clyde to propel a vessel, without sails 
 or oars, over the water — what do you think of that ? 
 — and that he had actually got a large boat to move 
 
90 
 
 THE WONDERS OF SCIENCE. 
 
 some three or four miles an hour by means of paddles 
 worked by a steam-engine on board the vessel.* 
 Dear, dear ! What shall we come to next, I wonder ! 
 They say in the paper, too, that the experiment was 
 perfectly successful; so that, I dare say, in a few 
 years our sailors will be no longer at the mercy of the 
 winds, and if they have only a stock of coals aboard, 
 they’ll be able to traverse the seas which way they 
 like. Ah ! coal is a wonderful thing, that it is, 
 Humphry. But I’m afraid that when we sit and 
 warm ourselves by the fire, we seldom give heed to 
 the dangers and hardships suffered by the poor 
 creatures who are far away under-ground, digging 
 it out of the bowels of the earth for us.” 
 
 “ That’s true enough,” interposed the doctor, 
 “ and it’s long been an opinion of mine that the 
 greatness of England will soon depend, not so much 
 on the energy of its people as the extent of its coal- 
 fields. You have heard, doubtlessly, that Mr. Mur- 
 doch, in our own county here, has, within the last 
 year or two, made a successful application of the 
 
 * W. Symington (according to Haydn’s Dictionary) made a 
 passage on the Forth and Clyde Canal in 17S9. In 1807, Fulton 
 started a steam-boat in America, on the river Hudson. In 1812, 
 steam-vessels first began plying on the Clyde ; but it was not till 
 the year 1815 that the first steam-vessel made its appearance on 
 the Thames. This was a boat from Glasgow ; for it was only in 
 that year the first steamer was built in England. Ten years after- 
 wards (1825) Captain Johnston received 10,000Z. for making the 
 first steam voyage to India in the Enterprise. In the year 1852 
 there were 1227 steam-vessels belonging to the United Kingdom. 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP, 91 
 
 gas from coal to the purposes of illumination ; he 
 has produced by it a light much more brilliant than 
 that of any lamp, and which requires no feeding 
 nor trimming, nor has it any wick ; and I am told 
 that he speaks confidently of its being possible to 
 light our streets and houses by such means.* But 
 I must confess, that I myself can hardly go with 
 the gentleman so far as that.” 
 
 “ Well, for my part, Bingham,” interrupted the 
 father, “ I am ready to believe anything. I have 
 lived to see mail-coaches introduced throughout the 
 country for expediting the post, and letters that 
 used to take near upon a fortnight to go from here 
 to London, now carried the same distance in little 
 more than two days.f So nothing they could do 
 
 * Gas was first evolved from coal by Dr. Clayton, in 1739. Its 
 application to the purposes of illumination was first tried by Mr. 
 Murdoch, in Cornwall, in 1792. Ten years after this (in 1802) 
 Bolton and Watt’s foundry, at Birmingham, exhibited the first 
 display of gas-lights during the rejoicings for peace. The first 
 manufactory permanently lighted by gas was a cotton mill at 
 Manchester — this was in 1805. Gas was first used for lighting 
 Pall Mall, in London, in 1809, and in 1814 it had become general 
 throughout the metropolis. The gas -pipes in and round London 
 are now said to be more than 1100 miles in length. 
 
 f Mail-coaches were first set up at Bristol, August 2, 1784, 
 and at the end of 1785 they became general in England. This 
 plan for the conveyance of letters was the invention of Mr. 
 Palmer, at Bath. The mails had previously been conveyed by 
 carts with a single horse, or by boys on horseback. From the 
 establishment of mail-coaches the prosperity of the Post-office 
 commenced. The year before their introduction the postal re- 
 venue was only 146,000Z. and it ultimately increased to 2,500,000/. 
 
92 
 
 THE WONDERS OF SCIENCE. 
 
 would astonish me after that ! No, not even if I 
 was to hear that the mail-coaches themselves were 
 driven by coals, and at twice the rate they go at 
 now.” 
 
 This was considered so wonderful a stretch of 
 imagination on the part of the old gentleman, that 
 the whole company laughed heartily at the apparent 
 impossibility of such an achievement. 
 
 “ You may smile,” went on the old man, “ but 
 steam is only in its infancy yet, depend upon it; 
 and the engineer at the Wherry Mine, when I 
 was talking to him about the machine there, told 
 me that there was force enough in a bushel, or 
 eighty-four pounds of coals, when properly con- 
 sumed, to raise 70,000,000 pounds weight one foot 
 high. Now, the ascent of Mont Blanc, from the 
 valley of Chamouni, is said by travellers to be 
 the most toilsome feat that a strong man can 
 execute in two days ; nevertheless, I find by cal- 
 culation” (and the old gentleman drew a bit of 
 paper from his waistcoat pocket), “ that the 
 combustion of only two pounds of coal would be 
 sufficient, by means of a steam-engine, to lift a 
 man to the summit. Again, the great Pyramid of 
 Egypt is composed entirely of granite, it stands on 
 eleven acres of ground, and is 500 feet high, so 
 that its entire weight has been calculated to be 
 about 13,000 million pounds; consequently about 
 180 bushels of coal would be sufficient to raise the 
 
THE FIRST GLIMMER OF THE SAFETY-LAMP. 93 
 
 entire mass twelve inches from its base.* So that 
 you see, Humphry, what a wonderful thing coal is, 
 and the large amount of force that lies locked up in 
 every pound of it.” 
 
 “ I do, sir,” said the boy, “ and it is this which 
 makes me wish to decrease the suffering attendant 
 upon the working of so valuable a mineral. The 
 account of the accident, which Dr. Borlase has just 
 told us, has so harrowed my feelings, that I shall 
 spare neither time nor labour in seeking to discover 
 the causes upon which such calamities depend, so 
 as to find out the means by which to prevent 
 them for the future. It may be some years before 
 I shall be able to perfect my plans, but perfected 
 they shall be one day if my life be spared ; and then 
 I have no fear that a discovery, having for its object 
 the preservation of human life and the diminution 
 of human misery, will be either neglected or for- 
 gotten. However high the gratification of possess- 
 ing the good opinion of society, there is a still more 
 exalting pleasure in the consciousness of having 
 laboured to be useful.” j* 
 
 * See Sir John Herschel’s “ Introduction to the Study of 
 Natural Philosophy.” 
 
 •f* These are Davy’s own words, being the concluding passage 
 of his work “ On the Safety-Lamp.” 
 
94 
 
 THE WONDERS OF SCIENCE. 
 
 CHAPTER VI. 
 
 THE WONDERS OF HEAT : ITS SOURCES. 
 
 Humphry was so full of his project, that all the day 
 long he could think of little else, and at night he lay 
 awake in his bed for many hours, planning an infinity 
 of rude schemes for accomplishing the object he had 
 in view. He devised and fashioned a number of 
 odd contrivances, too, for the purpose, but each in 
 its turn was found to be of little or no avail. 
 
 Nevertheless, the idea was too great to be hastily 
 abandoned, and the sense of the fame that success 
 in such an undertaking would assuredly give to his 
 name had entered so deep into the boy’s mind, that 
 he got to crave more and more for worldly honours ; 
 and he would sit of an evening, alone among the 
 rocks, dreaming of the time when he, a poor Cornish 
 boy, was to be ranked among the intellectually 
 noble, and reverenced throughout Europe for his 
 genius and his benevolence. 
 
 Nor did the lad fail, when he visited his mother, 
 to confide to her all his hopes of success and renown ; 
 and when the widow heard that he was bent on dis- 
 
THE WONDERS OF HEAT. 
 
 95 
 
 covering the means of saving the lives of the poor 
 miners — a class whom she had long learnt to pity, 
 for she had been brought up in the midst of them, 
 as it were — she felt prouder than ever of her darling 
 boy, and shed many a tear of joy over him. 
 
 Mrs. Foxell, too, when she beheld Humphry’s 
 vexation at the repeated failures of the models he 
 constructed, encouraged the lad in every way, re- 
 minding him that he himself had said the project 
 would cost him years of hard study to accomplish. 
 
 Accordingly, after many disappointments, Hum- 
 phry himself began to see that he could only hope 
 to attain the result he desired by making himself 
 acquainted with all that was already known upon 
 the matter. He was ignorant even of the laws of 
 combustion in general, and the rude experiments he 
 had made had set his mind craving for knowledge 
 on the subject. “ Why did this thing burn, and 
 that not ? ” he would inwardly inquire. “ How 
 came it that one body, as gunpowder for example, 
 went alight all of an instant, and another, like 
 tinder, took a long time to smoulder away ? And 
 why was phosphorous so easy to kindle, and wood, 
 comparatively, so difficult, that the slightest friction 
 would inflame the one, whereas it required a long 
 time to light the other by such means? What 
 mysterious process,” he would ask himself, “ went 
 on when any substance burst into flame, and whence 
 came the light and heat that were then given out 
 
96 
 
 THE WONDERS OF SCIENCE. 
 
 from materials that, a few moments before, had been 
 dark and cold? Could the light and heat have 
 been imprisoned in the substance, and were they set 
 free during the combustion ; or were these powers 
 generated merely by the burning of the bodies ? ” 
 Then Humphry’s mind darted off to the deeper 
 question, “ What were the principles of light and 
 heat themselves ? Were they one and the same, or 
 two distinct powers in nature ? In a winter’s day*” 
 he mused, “ we have the same light from the sun, 
 and but little heat ; whilst in all cases of artificial 
 illumination there is great heat and but little light, 
 compared with that of the solar rays.” 
 
 These and many other such puzzling inquiries 
 passed through Humphry’s brain, and left his mind 
 in such a state of perplexity that he could not rest 
 without a clearer insight into the subject. He soon 
 saw, too, how silly he had been in setting to work 
 before he had availed himself of the discoveries of 
 those who had gone before him ; for, he would say, 
 how could he think of finding out, by himself, all 
 that was known of the science of heat and light, 
 when each of those sciences, as Mr. Tonkin had told 
 him, had taken thousands of the wisest minds — ay, 
 and thousands of years of intense study — to build up ; 
 for in them was contained the accumulated expe- 
 rience of all mankind from all time. Yet, because 
 the truths were free to the world, he had refused 
 to avail himself of them, and, like a proud fool, had 
 
THE WONDERS OF HEAT. 
 
 97 
 
 thought he could compass his end without any such 
 knowledge at all. 
 
 It was not long before Humphry was hard at 
 work making himself master of the laws of heat. 
 He had borrowed of Mr. Tonkin the best book then 
 extant upon the subject, and often when the streets 
 of the little town in which he lived were silent as 
 the tomb — and the distant bell of Madern Church, 
 as it tolled the morning hours, was heard to boom 
 upon the still air, almost like a moan — and the sound 
 of the waves that rippled upon the neighbouring 
 shore stole on the ear softly as the murmur of a 
 sea-shell — the candle might be seen burning in the 
 boy’s chamber, making the little diamond panes of 
 the casement shine like plates of amber in the dark- 
 ness (for every other window in the street looked 
 black from the want of light), while the observant 
 eye could trace on the white wall on one side of the 
 room, the huge distorted shadow of the lad bending 
 over his books. 
 
 As Humphry read on, and got to see clearer and 
 deeper into the nature and properties of the subtle 
 principle he was studying, he grew more and more 
 enraptured with the wonders and the knowledge 
 that were opened up to him at every step ; and often 
 when some new discovery burst upon his mind he 
 would, in the fervour of his admiration, fall upon 
 ms knees, there alone in his chamber at night-time 
 
 H 
 
98 
 
 THE WONDERS O'F SCIENCE. 
 
 and thank God that he had come to know so much 
 of His goodness and glory ; then he would rebuke 
 himself, too, for having remained so long ignorant 
 of the many beauties that lay concealed in the wis- 
 dom and exquisite fitness with which the phenomena 
 of the universe are linked together. “ What fairy 
 tale of enchantment,” he would say to himself, “ can 
 display magic like this ? What work of human 
 invention can fill the mind with such amazement 
 and delight at the subtlety of the art, as the mind 
 feels when it first learns the wondrous story of 
 Creation ? ” 
 
 When Humphry had read through the books that 
 he had obtained of Mr. Tonkin and Mr. Borlase, 
 he proceeded to repeat the most striking of the ex- 
 periments in connexion with the subject, so as to 
 impress the knowledge more firmly on his mind. 
 But before doing this he reviewed the whole mat- 
 ter, and arranged it after his own manner — for he 
 was not the boy to follow in a beaten track, and 
 found no little delight in the exercise of his own 
 genius. 
 
 “ First,” said Humphry, as he pondered over the 
 science of heat in general, “ the sources of it have 
 to be considered ; that is to say, whence is the heat 
 of the earth derived ? The universe is a vast re- 
 servoir of caloric, and it is capable of being evolved, 
 by some means or other, from almost every substance 
 
THE WONDERS OF HEAT. 
 
 99 
 
 that surrounds us ; and though its production arti- 
 ficially is now so common that it has lost all wonder 
 with us, there must have been a time when the 
 elimination of it from substances on the earth must 
 have been a matter of such amazement as to have 
 produced a feeling of awe, on the part of the multi- 
 tude, towards those who first discovered the art. 
 This, perhaps,” the boy went on, “ is the origin of 
 the fable of Prometheus, who was, probably, the 
 first man who found out the way to kindle a fire, 
 and so was thought to have stolen the heat from 
 the sun. Tradition says, the first artificial fire was 
 produced by lightning striking a decayed tree. 
 Our minds can, even now, almost conceive the 
 terrible awe of the people who first witnessed the 
 liberation of fire on the earth — who beheld, for the 
 first time, the transparent red flames burst forth 
 from the combustible and lick the air like burning 
 tongues, while the smoke rolled upwards from them 
 in dense leaden clouds. Then the intense pain felt 
 on touching the fire must have made the populace 
 almost believe that they had been stung by demon 
 serpents, while the roar of the wind, as it rushed 
 towards the blazing mass to supply the place of the 
 lighter air that had been driven upwards by it, 
 must have sounded to the people like spectral 
 voices, and the ultimate dissipation of the huge 
 solid substance into invisible gases must have ap- 
 peared like the most marvellous magic to them. 
 
100 
 
 THE WONDERS OF SCIENCE. 
 
 Thus it came that men at last got to worship the 
 fire, for its wonder and its terror, though we kindle 
 it nowadays almost without a thought or a fear.” 
 
 “ The sources of heat at present known to man,” 
 continued the boy, as he wrote down the divisions 
 of the subject in his note -book, “ are many. 
 First, there is the heat of the sun , and , perhaps , 
 that of the moon ; philosophers, however, have 
 concentrated the moonbeams upwards of 300 times, 
 by means of a burning-glass, nearly 3 feet in dia- 
 meter, and yet the most delicate thermometers have 
 shown not the least increase of temperature. This 
 is said to arise from the feebleness of the light of 
 the moon, as compared with that of the sun ; for the 
 lunar rays have been calculated to possess 300,000 
 times less illuminating power than the solar ones, 
 whilst the light of the sun itself has been shown by 
 experiment to have 12,000 times the intensity of the 
 flame of a wax-candle, so that a little fragment of 
 the great luminary the size of such a flame would 
 possess the illuminating power of 12,000 wax- 
 candles ; and, since the diameter of the sun is nearly 
 four times greater than the distance of the earth 
 from the moon, this may give us soigae notion of the 
 vast flood of light and (if the two are connected) of 
 heat that are being continually streamed forth from 
 the sun into the universe. Of the intensity of the 
 solar heat , the law of the decrease of all radiant 
 matter enables us to form some conception ; for this 
 
TOE WONDERS OF HEAT. 101 
 
 teaches us that the heat of the sun’s rays, after 
 travelling to the distance of the earth, must be 
 diffused over at least 300,000 times a greater space 
 than it is at the sun itself, and consequently that 
 the intensity of the heat must be that number of 
 times more highly concentrated at the sun’s surface 
 than it is on reaching our atmosphere. Now, one 
 of the largest burning mirrors that have ever been 
 constructed, and which had the power of concen- 
 trating the sun’s rays rather more than 17 ? 000 
 times, melted a piece of Pompey’s pillar in less than 
 a minute, a piece of cast-iron in a quarter of a 
 minute, a copper halfpenny in sixteen seconds, and 
 fragments of slate and tile in three and four seconds. 
 A lens that increased the intensity of the sun’s heat 
 about 10,000 times fused pieces of platinum, gold, 
 asbestos, quartz, &c. in three seconds ; so that — 
 as the solar fire must, at the sun itself, be 30 times 
 more intense than the calorific power of its rays, 
 even when thus concentrated, at the surface of the 
 earth — it is evident that the fury of the sun’s heat 
 must at its source be sufficient to dissipate the most 
 obstinate metals in vapour, and to make the most 
 infusible of the earths as liquid as glass. 
 
 “ Then, again, there is the heat of the stars ; 
 for if each of these be suns, and they, like our own 
 sun, give off heat, together with light, while the 
 heat radiated by them decreases in the same pro- 
 portion as their light, it is clear that the united 
 
102 
 
 THE WONDERS OF SCIENCE. 
 
 beams of the starry host must give a certain general 
 temperature to the realms of space. This tempera- 
 ture philosophers have calculated to be as low as 
 that at which quicksilver freezes, and which degree 
 of cold appears to be attained in the Arctic regions, 
 during the long absence of the sun through a polar 
 winter. According to the principles which regulate 
 the radiation of light and heat, it is demonstrable 
 that the starbeams can only maintain a temperature 
 in infinite space which, when compared with the 
 heat we derive from the sun, must be as much in- 
 ferior to it as the light of a moonless midnight is to 
 the light of midday at the equator ; and it is plain, 
 that the rate at which the earth cools down or 
 radiates back into space the heat it receives from 
 the sun must have its limit in the temperature of 
 planetary space itself, so that, had this been higher 
 or lower, the earth’s surface must have been hotter 
 or colder than it is. 
 
 “ But, besides the preceding celestial sources of 
 heat in nature, we must also (if we suppose that 
 such things as give light to the earth radiate heat 
 as well to it — though in ever so minute a degree) 
 enumerate that peculiar cone or pyramid of luminous 
 mist which is seen an hour or two after sunset, at 
 certain months of the year, in the line of the ecliptic, 
 and to which astronomers have given the name of 
 ‘ the zodiacal light* Travellers in tropical regions 
 tell us that this is sometimes so brilliant that it 
 
THE WONDERS OF HEAT. 
 
 103 
 
 seems a second sunset, lasting almost to midnight, 
 and that the clouds which are scattered over the 
 deep azure of the distant horizon appear to flit past 
 the glowing nebulosity as before a golden curtain, 
 while above these other clouds are seen reflecting 
 from time to time brightly variegated colours. 
 
 “ Then, again, there are the brilliant corusca- 
 tions of the aurora borealis (or ‘ northern dawn ' 
 or ‘ polar light' as it is sometimes called), though 
 this appears to be rather an emanation from the earth 
 itself than any celestial phenomenon. According 
 to the best accounts, the light of the aurora exists 
 almost within the bounds of our own atmosphere, 
 and seems to stream from one of the poles of our 
 globe, as if the earth had suddenly acquired the 
 power of becoming self-luminous like the stars and 
 sun.* This brilliant exhalation is rendered more 
 interesting by the fact, that the great Herschel 
 himself, from repeated observations of the spots 
 on the sun, came to the conclusion that such 
 spots are parts of the dark solid body of the sun 
 itself, laid bare to our view by fluctuations in the 
 solar atmosphere, and that from that atmosphere 
 alone the light and heat proceed — the shining matter 
 
 * Professor Challis, of the Cambridge University, calculated the 
 height of the bow of light proceeding from the aurora (seen at 
 Cambridge, March 9, 1847) to be 177 miles above the surface of 
 the earth. The limits of our own atmosphere are placed, by Sir 
 John Herschel, at the 100th part of the diameter of the globe, or, 
 in round numbers, 80 miles above the surface. 
 
104 
 
 THE WONDERS OF SCIENCE. 
 
 of the sun being, not a fluid, but a mass of brilliant 
 or phosphoric clouds, glowing with the beams of 
 the luminous strata of the solar atmosphere far 
 above them — in the same manner as the aurora 
 with us is said sometimes to illuminate a stratum 
 of clouds below it. 
 
 “It is impossible to say what increase of heat 
 our atmosphere may derive from the beams of the * 
 aurora and the zodiacal light, but as we have no 
 reason for supposing the rays in these cases to be 
 destitute of all heat, it is evident that, when enume- 
 rating the several sources of caloric in the universe, 
 some mention should be made of them; for who 
 can tell what would have been the effect upon the 
 general stock of heat in nature without such phe- 
 nomena, or how low the temperature of the earth’s 
 surface might have been if the heat of the planetary 
 space in which it moves had been less than it is ? 
 
 “ But a far more important source of caloric to 
 the earth lies in its subterranean heat , or the in- 
 crease of temperature which is found to ensue as we 
 descend below the surface of our globe. Carefully 
 conducted experiments have shown that, in our own 
 climate, the temperature increases about 1° for every 
 50 feet that we go down. At 354 feet below the 
 ground the heat is found to be 60°, in those parts 
 where the surface of the earth itself has a mean 
 temperature of but 50°. At 792 feet under the 
 soil the thermometer rises to 70°; at 1434 feet it 
 
THE WONDERS OF HEAT. 
 
 105 
 
 marks 80°; at 1872 feet it reaches 90°; whereas 
 at 2556 feet it is as high as 100°. Now, if this 
 rate of increase (viz. 1° in every 50 odd feet) 
 continued uniformly as we descended, it would 
 follow that, at a depth of rather less than 2 miles, 
 water would be constantly at the boiling point, 
 and at 9 miles below the surface everything would 
 be red-hot, whilst at rather more than 20 miles the 
 granite rocks themselves would be in a continual 
 state of fusion. In the c United Mines 9 of Cornwall 
 one of the levels is so hot, that though a stream of 
 cold water is allowed to flow through it, in order to 
 reduce the temperature, the miners are compelled 
 to work nearly naked, and will bathe in water at 
 80° to cool themselves. At the Tresavean Mine, 
 in the same county, which is nearly 2000 feet deep, 
 the temperature is greater than the intensest heat 
 of summer in the dog-days. 
 
 “ There is, however, no evidence to prove that 
 the increase of temperature beneath the surface 
 proceeds at a uniform rate when we descend to a 
 greater depth than 1500 feet below the level of the 
 sea. It will be seen by the rates of increase above 
 given that the temperature underground rises at 
 first 1° in every 35 \ feet, whereas at great depths 
 the increase amounts only to 1° in every 68 feet ; 
 and, as far as our observations have extended, the 
 subterranean heat appears to bear a close relation 
 to the thermic condition of the climate at the sur- 
 
106 
 
 THE WONDERS OF SCIENCE. 
 
 face ; for it is found, on descending to a depth of 
 about 60 feet in our own climate, the heat of the 
 earth no longer fluctuates with the different seasons, 
 but remains always at the same point during winter 
 and summer, whilst at the tropics the stratum of 
 invariable temperature is situate at only 1 foot below 
 the soil. 
 
 “ But whether the subterranean heat be due to 
 the absorption of the solar rays, or whether it arises 
 (as some have supposed) from a vast body of central 
 fire in the earth, it is certain that we have many 
 indications of prodigious elevations of temperature 
 beneath the soil. These appear to be due to great 
 chemical changes taking place in the substances 
 forming the crust of the earth. Every schoolboy 
 knows that a mixture of sulphur and iron-filings 
 buried under the ground will, in a short time, 
 become so heated as to burst into flames. Now 
 these two materials form the mineral called ‘ iron 
 pyrites/ which prevails through every coal-field, 
 and the moisture acting on these is known to gene- 
 rate heat enough to inflame neighbouring combust- 
 ibles — many coal-mines having been set on fire 
 spontaneously by such means. In the 6 United 
 Mines/ where the heat is found so oppressive, it is 
 undoubtedly owing to the decomposition of immense 
 quantities of pyrites that are known to exist at a 
 short distance from the works. 
 
 “ Of the prodigious subterraneauJkbaf existing 
 
THE WONDERS OF HEAT. 
 
 107 
 
 in some parts of the earth we have the most un- 
 mistakeable evidence. In some places boiling hot 
 springs — as the Geysers of Iceland — issue from the 
 ground (in these eggs have been cooked in 4 mi- 
 nutes) ; and even in our own country the wells of 
 Bath have a temperature of 115°, while at those of 
 Carlsbad, in Bohemia, the heat of the water is as 
 high as 167°. In other parts, 4 fumaroles 9 or 
 eruptions of steam, burst from the soil ; while in 
 others there are 4 solfataras 9 or jets of sulphurous 
 vapour; and in others, again, — as in the valleys 
 of the Eifel, at the lake of Laach in Germany — 
 4 mofettes ,’ or vast exhalations of carbonic acid gas, 
 occur. Further, there are Artesian fire-springs — 
 like those termed 4 ho-tsing 9 in China, where a pro- 
 vince has been lighted (by the gas issuing from 
 them) for several thousand years. Moreover, erup- 
 tions of boiling acid mud, called 4 salses 9 are not 
 unfrequent. The volcano at Carguaraizo, in Peru, 
 threw up a torrent of hot mud in the year 1698, 
 that covered nearly 80,000 acres of ground ; and in 
 1797, an entire village near Rio Bambo was buried 
 under a similar mass. 
 
 44 All these phenomena are evidences of intense 
 subterranean heat, many of them being simply the 
 products of underground combustion : but lofty jets 
 of flame have likewise been known to blaze up from 
 the earth, to such a height that they could be seen 
 at a distance of 24 miles from the eruption ; as, for 
 
108 
 
 THE WONDERS OF SCIENCE. 
 
 instance, at the village of Baklichli, near Baku, on 
 the Caspian Sea. During earthquakes , too, the 
 earth has been known to open and to vomit forth 
 flames, and gases, and enormous fragments of rocks, 
 accompanied with a noise of subterranean thunder ; 
 while in some places the heaving soil has been 
 inflated by the force of the compressed vapours 
 beneath, and expanded like a bladder filled with air. 
 Such was the case among the plains of Malpais in 
 Mexico, in the month of September, 1759, when a 
 tract of ground, 3 to 4 miles in extent, rose up like 
 a huge bubble — flames bursting from the earth the 
 while over more than half a square league — and the 
 volcano of Jorullo being formed at the summit. 
 
 “ In volcanoes , or burning mountains, again, we 
 have manifestations of the intense elevation of tem- 
 perature existing at certain places within the crust 
 of the earth. The explosions from the volcano of 
 Guacamayo, in South America, are heard almost 
 daily at a distance of 80 miles ; whilst the noise of 
 the detonations from one in the Sunda Islands, near 
 Java, have been distinguished 970 miles from the 
 spot. But the most remarkable instance on record 
 of the fury and power of the subterranean fires is 
 to be found in the eruption of one of the Icelandic 
 volcanoes, called ‘ Skaptaa Jokul,’ which occurred 
 on the 8th of June, 1783. During this eruption the 
 large river Skaptaa entirely disappeared, and the 
 day after, a torrent of burning lava rushed down the 
 
THE WONDERS OF HEAT. 
 
 109 
 
 sides of the mountain and not only filled, but over- 
 flowed the channel of the stream, though in many 
 places it was 600 feet deep and 200 feet broad. 
 Then pursuing the course of the river, the fiery 
 current poured over a lofty cataract, and filled up 
 in a few days an enormous cavity that the waters 
 had been hollowing out for ages. A short while 
 after this another large river, the Hverfisfliot, dis- 
 appeared from its bed, and this was filled up by 
 another fiery torrent, which overflowed the country 
 in one night to the extent of more than 4 miles. 
 It has been estimated that these two streams of 
 burning molten rocks were together 90 miles in 
 length by 20 odd miles in breadth, and, in some 
 places, between 500 and 600 feet deep, while there 
 were in the aggregate forty thousand million tons 
 of red-hot rock poured out of the bowels of the 
 earth in the short space of ten weeks, during which 
 the eruption lasted.* 
 
 “ Another of the natural sources of heat to the 
 earth is to be found in the electric discharges 
 known under the names of forked and sheet light- 
 
 * To give a just idea of this fearful event it should be added, 
 that, at the most moderate calculation, 1300 human beings lost 
 their lives through the eruption ; it likewise caused the death of 
 20,000 horses, 7000 horned cattle, and 130,000 sheep. The 
 fisheries on the southern coast of the island, moreover, were 
 destroyed by it; and Iceland has not to this day, it is said, 
 recovered from the disastrous event of the year of the eruption 
 of Skaptaa Jokul. 
 
110 
 
 THE WONDERS OF SCIENCE* 
 
 ning. Of lightning there appear to be three kinds . 
 (1) The zigzag , which is linear and sharply defined 
 at the edges ; (2) the sheet , which illuminates whole 
 clouds, that seem to open and reveal the light within 
 them ; and (3) the globular , which appears in the 
 form of fire-balls. The two first of these kinds last 
 but for the thousandth part of a second, while the 
 globular form moves much more slowly. Of the 
 amount of heat contained in each of the different 
 species we have no precise knowledge, though, from 
 the experiments by which we produce discharges of 
 electricity artificially, on a small scale, we learn that 
 it must be considerable. If a spark which is drawn 
 from a small Leyden j ar, and which has force enough 
 to leap only some few inches through the air, has 
 power to inflame combustibles, and even to fuse the 
 metals in an attenuated form, what must be the 
 heat evolved from an electric discharge where the 
 insulating body consists of whole acres of clouds 
 rather than a few square inches of tin-foil, and 
 whence the fluid has power to leap through hun- 
 dreds of feet of the atmosphere towards the nearest 
 conductor ? That the electric flash possesses great 
 heating power, we have repeated proofs ; for it 
 melts all wires that are not sufficiently substantial 
 to allow it a free passage, inflames decayed trees, 
 overthrows buildings, and often fuses even the 
 rocks themselves — the tubes called ‘ fulgurites ,’ 
 which occur in beds of sandstone, and consist of 
 
THE WONDERS OF HEAT. 
 
 Ill 
 
 fused sand (glass), are known to geologists to have 
 been produced by such means — while at Funzie, 
 in Fetlar, the lightning is recorded to have torn up 
 a rock 105 feet long from its bed, and hurled the 
 fragments to a considerable distance from the spot. 
 Moreover, the electric heat is the greatest that we 
 are enabled to produce artificially, and so much ex- 
 ceeds that of the strongest furnace, that platinum, 
 which remains stubborn and infusible in a forge at 
 a white heat, melts in the arc of flame produced by 
 a powerful voltaic battery — like wax. 
 
 “ These are the natural sources of heat,” the 
 youth wrote on ; “ the artificial methods of gene- 
 rating heat, however, are much more various. We 
 can evolve heat by mechanical means — as, for in- 
 stance, by 'percussion or pressure . The blacksmith 
 hammers a nail until it becomes red hot, and from 
 it he lights his match ; and in coining, the blank 
 piece of metal becomes greatly heated by the 
 sudden and violent action of the press. By the 
 compression of air in a small tube, by means of a 
 condensing syringe, a sufficient quantity of heat 
 may be evolved to light German tinder ; and it has 
 been well said, ‘ that, locked in a pint measure of 
 air, there exists sufficient heat to make several 
 square inches of metal red hot.’ A piece of Indian- 
 rubber, suddenly and forcibly drawn out, becomes 
 warm in consequence of the extension, as may be 
 easily perceived by applying it to the lip the 
 
112 
 
 THE WONDERS OF SCIENCE. 
 
 moment it is stretched. Again, by the concussion 
 of a flint and steel so much heat is produced that 
 the sparks which fly off consist of small particles of 
 iron that have been fused by it. Moreover, when 
 a few grains of fulminating silver are struck by a 
 hammer, the heat produced is sufficient to ignite 
 gunpowder and to cause a violent explosion. 
 Again, friction is a prolific source of heat. The 
 Indian ignites two pieces of wood by rubbing them 
 together ; and even two pieces of ice may be made 
 to melt each other by the same means. It has been 
 truly observed, too, that an unlimited supply of 
 heat seems capable of being derived by friction 
 from certain materials. Water has been made to 
 boil in two hours and a-half, merely by boring 
 into a mass of metal that was surrounded by the 
 fluid. 
 
 “ But not only can we produce heat artificially 
 by mechanical means ; we can do so far more 
 plentifully and easily by chemical action, for it has 
 been found, that whenever two or more substances 
 rapidly combine, heat is invariably produced. In 
 fermentation (which is nothing more than a de- 
 composition of elements loosely united, and their 
 re-union in a more perfect state of combination) 
 considerable increase of temperature takes place. 
 During the making of vinegar there is much heat 
 evolved — the temperature rising, in some processes, 
 from 60° to 85°. Again, in the process of respira- 
 
THE WONDERS OF HEAT. 
 
 113 
 
 tion (which is merely the combination of the char- 
 coal in the blood, with a certain portion of the air 
 drawn into the lungs) the heat evolved is sup- 
 posed to be the cause of our bodies remaining 
 almost at a constant temperature. A little powder 
 of the metal called antimony thrown into a jar 
 of chlorine gas spontaneously ignites and burns 
 with brilliancy, combining with the gas so readily 
 that it takes fire and produces at first a liquid, 
 and afterwards a soft solid called the ‘ butter 
 of antimony.’ Further, there is an oil-like fluid 
 consisting of two gases (nitrogen and chlorine) 
 that have been made to unite with each other, and 
 this compound has such an affinity for combustible 
 bodies, that even if a long rod, the extremity 
 of which has been dipped in oil, be made to touch 
 only a globule of it — the size of a mustard-seed — 
 confined under water, it instantly explodes with 
 a flash of light, and with such violence that it 
 disperses the water in a shower, and breaks into 
 atoms the vessel in which it is contained ; so that 
 experienced chemists always protect the face by a 
 mask when making the experiment. Again, if oil 
 of vitriol and spirits of wine, or if aqua fortis and 
 spirits of turpentine, be suddenly mixed, sufficient 
 heat is set free to ignite the spirits. When caus- 
 tic potash, too, dissolves in water, a considerable 
 increase of temperature ensues. So if spirits of 
 wine and water are mixed together, the mixture 
 
 i 
 
114 
 
 THE WONDERS OF SCIENCE. 
 
 becomes much hotter and occupies a smaller space ; 
 whilst if four parts of strong oil of vitriol be mixed 
 with one part of snow or pounded ice, the heat 
 developed is sufficient to boil water, whereas if one 
 part of the acid be added to four parts of snow, 
 intense cold is produced. More than this, if a piece 
 of clean platinum be immersed in a vessel con- 
 taining a mixture of oxygen and hydrogen gases, 
 such intense heat is evolved that the metal becomes 
 suddenly red-hot, and the gases are made to com- 
 bine so rapidly that a violent explosion ensues, and 
 the two gases become water. 
 
 “ But the most ordinary mode of obtaining heat 
 artificially is combustion , though this is merely 
 a process of rapid combination after all. It is by 
 the heat evolved during the process of combustion 
 that our houses are warmed in winter, our food 
 cooked, the steam-engines of our factories and 
 mines set in motion, our metals smelted, cast, and 
 wrought, our glass made, our dishes hardened, and 
 an infinity of useful services rendered to us ; in- 
 deed, so much do we owe to combustion, that we 
 are unable to comprehend the state which man 
 must have been in before the method of producing 
 heat artificially by such means was discovered. 
 
 “ Lastly, there is the heat generated by nervous 
 energy; for if the sole source of warmth to the 
 animal frame lay in the chemical processes that 
 are continually going on within it, why should a 
 
THE WONDERS OF HEAT. 
 
 115 
 
 suddenly excited emotion (as in states of anger and 
 blushing) have power to produce so considerable 
 an increase of temperature in the human frame? 
 Indeed we have personal knowledge, that almost 
 every muscular movement produces sensible warmth, 
 even as any violent excitement of the mind is at- 
 tended with the same result. We know, too, that 
 the injury of one little thread-like nerve can reduce 
 a member of the body to a state of stony coldness ; 
 and that after death, when the chemical decom- 
 positions are proceeding as actively as during life, 
 the body possesses no animal heat whatever.” Phy- 
 siologists, moreover, have shown that, if the respi- 
 ration be kept up artificially in an animal after its 
 head has been cut off, the blood becomes arterial- 
 ized, and the several chemical changes go on as 
 during life , — but without the body being in the least 
 warmed by them . 
 
116 
 
 THE WONDERS OF SCIENCE. 
 
 CHAPTER VII. 
 
 THE WONDERFUL DIFFUSION OF HEAT. 
 
 When Humphry had written thus far concerning 
 the sources of heat (for the boy was delighted to 
 note down his thoughts on the various subjects he 
 was studying*), he began to ponder over the 
 several modes in which heat was communicated to 
 bodies removed from the different sources of it ; 
 for, said he to himself, “ if there had been no means 
 of propagating heat from one part of space to an- 
 other, the fires could not have warmed us, and the 
 sun would have been only a moon to our globe, 
 while we should have been deprived of some of our 
 most agreeable sensations. Hence, in the considera- 
 
 * The note-books of Davy during the time of his apprenticeship 
 have been preserved, and show (says his brother) “ the ardour 
 with which he entered upon his studies, and the extensive reach 
 of his mind in the various branches of knowledge which he pro - 
 posed to pursue. One of them, bearing the date of 1795, is,” 
 (Dr. John Davy adds,) “ on many accounts, a literary curiosity. 
 It is a small quarto, with parchment covers. Outside one of the 
 covers is the figure of an ancient lyre drawn with his pen, and on 
 the other an olive leaf encircling a lamp ; as if,” remarks his 
 biographer, “ in anticipation of his great discovery of confining 
 
THE WONDERFUL DIFFUSION OF HEAT. 117 
 
 tion of such a subject, it becomes necessary to attend 
 to, and distinguish between, the several ways in 
 which a body at an elevated temperature commu- 
 nicates its heat to others that are either in contact 
 with it or at a distance from it, as well as the 
 several conditions which determine the reception or 
 absorption of the heat by different substances. 
 
 dame in the safety -lamp. At the commencement of it is the fol- 
 lowing plan of study : — 
 
 1. Theology; 
 
 Or Religion, Ethics, 1 f Taught by Nature. 
 
 or moral virtues, / L ,, by Revelation. 
 
 2. Geography. 
 
 3. My Profession. 
 
 1. Botany. 
 
 2. Pharmacy. 
 
 3. Nosology. 
 
 4. Anatomy. 
 
 5. Surgery. 
 
 6. Chemistry. 
 
 4. Logic. 
 
 6. Physics. 
 
 1. The doctrines and properties of natural bodies. 
 
 2. Of the operations of nature. 
 
 3. Of the doctrines of fluids. 
 
 4. Of the properties of organised matter. 
 
 5. Of the organisation of matter. 
 
 6. Simple astronomy. 
 
 7. Mechanics. 9. History and Chronology. 
 
 8. Rhetoric and Oratory. 10. Mathematics. 
 
 To give some distinct idea of the bent of his studies at this time,’ , 
 continues his brother, “ I shall briefly notice the principal topics 
 which appear in this MS. volume. It opens with ‘ Hints towards 
 the Investigation of Truth in Religious and Political Opinions , 
 composed as they occurred, to be placed in a more regular manner 
 hereafter.’ His first essay is * On the Immortality and Immate - 
 
 5. Language. 
 
 1. English. 
 
 2. French. 
 
 3. Latin. 
 
 4. Greek. 
 
 5. Italian. 
 
 6. Spanish. 
 
 7. Hebrew. 
 
118 
 
 THE WONDERS OF SCIENCE. 
 
 “ Now, heat may be communicated from one body 
 to another in three different ways, — 
 
 1 . By emission of rays of heat from a distance ; 
 
 2. By conduction along the particles of a solid 
 
 body; 
 
 3. By convection or circulation among the par- 
 
 ticles of a fluid. 
 
 riality of the Soul;' the second bears the title of l Body, orga- 
 nised matter and his third is ‘ On Governments .’ Then there 
 
 follow a variety of essays on metaphysical and moral subjects. 
 These topics occupy more than one -half of the book ; the other 
 part, which appears to have been written after, commences at the 
 opposite end, inverted. This is devoted partly to religious essays ; 
 but besides these,” adds Dr. Davy, “ there are some verses and 
 the beginning of a romance, called ‘ An Idyl, 1 which is in the 
 form of dialogue, the characters being ‘ Trevelis a warrior and 
 friend of Prince Arthur, and Morrobin a Druid;’ the scene, 
 1 A cliff at the Land’s End in Cornwall.’ 
 
 “ From the same source of information — his note-books — 
 it appears, that in the beginning of the year 1796 he entered 
 on the study of mathematics. One book is almost entirely 
 confined to this subject, and he seems to have finished the 
 elementary course in more than twelve months, when he was 
 commencing the eleventh book of Euclid, having gone through 
 most of the other branches. He engaged in these studies with- 
 out a master, and perfectly voluntary on his part, from the con- 
 viction of their usefulness preliminary to the study of chemical 
 and physical sciences. His passion for poetry at the same time 
 appears to have kept pace with the expansion of his faculties, and 
 not to have been damped even by the application to mathematics, 
 for his early note-books contain many desultory verses. His 
 early chemical reading was confined to two works of a very diffe- 
 rent description, ‘ Lavoisier's Elements of Chemistry and 
 * Nicholson's Dictionary of Chemistry.' This new study seems 
 very soon to have excited in his mind a most lively interest. He 
 was not satisfied with merely reading and acquiring the ideas cf 
 others. He criticised the theoretical views of the great French 
 
THE WONDERFUL DIFFUSION OF HEAT. 119 
 
 “ The propagation of heat by the emission of heat- 
 rays from a warm or burning body at a distance, is the 
 one that first demands attention. This mode of com- 
 munication is generally styled ‘ radiation ofheat]&rA 
 it is evident that the heat-rays emanating from one 
 body may be communicated to another, either directly, 
 by the process of transmission through the intervening 
 substances, or indirectly, by reflexion from the sur- 
 faces of those opposing them; for the heat-rays, 
 like those of light, always proceed in a straight line, 
 and are susceptible, likewise, of being reflected or 
 driven off at an equal angle from polished surfaces.” 
 
 philosopher” (Lavoisier, the author of the new Theory of Com- 
 bustion, which was propounded only some few years before); 
 “he doubted, rejected, and advanced speculations of his own. 
 Speculation appears to have led him to experiment, and experiment 
 to further speculation, with such rapid progress that in a few 
 months he had formed a new hypothesis (concerning the principle 
 of heat) , and flattered himself that he had triumphed over an im- 
 portant part of the doctrine of the French school. 
 
 “ Humphry Davy himself writes in one of his note-books, 
 dated 1799, * About twenty months ago I began the study of 
 Chemistry. The system of Lavoisier, almost the only elementary 
 book in my possession, was the first that I studied.’ ” That the 
 subject of heat was the first chemical principle that engaged the 
 boy’s attention we have further evidence in the fact, that, a few 
 years afterwards, his “ Researches on Heat and Light ” were pub- 
 lished in the form of essays, in a miscellaneous volume edited by 
 Dr. Beddoes. In the preface to this work the editor says, re- 
 ferring to the views propounded by Davy, 1 It is not neces- 
 sary, in praise or excuse of his system, to add that at the time 
 the theory was formed the author was under twenty years of age, 
 pupil to a surgeon-apothecary in the most remote town of Corn- 
 wall, with little access to philosophical books, and none at all to 
 philosophical men.’ ” 
 
120 
 
 THE WONDERS OF SCIENCE. 
 
 Having settled thus much in his own mind, and 
 arranged the subject with that logical precision 
 which was a marked feature in the genius of the 
 youth, he proceeded to test experimentally the 
 emissive energies, or, in other words, the radiating 
 powers of different substances. 
 
 For this purpose he provided himself with a 
 square tin canister: one of the four sides of this 
 he brought to as high a polish as he possibly could; 
 the second side he coated with a mixture of lamp- 
 black and gum-water ; over the third side he 
 pasted a piece of paper, and the fourth he covered 
 with glass. Then, having provided himself with a 
 thermometer from the surgery below, he proceeded 
 to arrange the canister at some distance from the 
 thermometer, but on a level with it. After this he 
 filled the canister with boiling-hot water, and then 
 proceeded to note how the thermometer was affected 
 when the canister was turned round, and each of 
 its sides successively brought before the instrument. 
 The boy soon ascertained, to his great joy, that the 
 heat was thrown off most rapidly from the blackened 
 side of the canister ; next to that, he found the 
 surface covered with paper to radiate heat more 
 rapidly than the other two ; then the glass side 
 was discovered to possess more emissive power 
 than the polished surface, while the polished sur- 
 face itself had the least radiating power of all. 
 
 Delighted with the result of the experiment, and 
 
TIIE WONDERFUL DIFFUSION OF HEAT. 
 
 m 
 
 pleased with the knowledge it gave him as to the 
 emissive energies of different substances for heat, 
 the boy, to assure himself that he was not mis- 
 taken, held his hand at a short distance from the 
 canister, and caused the differently-coated sides to 
 pass successively before it. As he did so, he could 
 feel the heat increase gradually as the polished side 
 passed from before his hand and the blackened one 
 came round in front of it ; so that, had he not been 
 aware of the fact, he would hardly have believed 
 that the water in the canister was as hot at that 
 part where the bright tin had been left as it was 
 where the side had been blackened over. 
 
 Next the lad tried another modification of the 
 same experiment. Having blackened one canister 
 entirely over, and brightly polished the outside of 
 another which was of the same size, he filled the 
 two vessels with boiling water, and putting a ther- 
 mometer into each he placed them upon a table at 
 opposite corners of an empty room, and then found 
 that the thermometer in the blackened vessel fell 
 much quicker than that in the polished tin one ; so 
 he now saw that the reason why the black side of 
 the canister in the first experiment felt hotter than 
 the polished surface did to his hand was, that the 
 water there was parting with its heat at a more 
 rapid rate, so that in the entirely blackened vessel 
 it necessarily cooled down sooner than in the 
 bright tin one. 
 
122 
 
 THE WONDERS OF SCIENCE. 
 
 Humphry was so delighted with the truths he 
 had thus discovered, that he tried a number of 
 other experiments as to the radiating power of dif- 
 ferent substances, and at last came to the con- 
 clusion that lamp-black, sealing-wax, wool, paper, 
 glass, and black-lead, were much better radiators 
 of heat than the metals ; their power of giving 
 off heat being in the order in which they are 
 here mentioned, — a surface of lamp-black cooling 
 quicker than one of sealing-wax, and sealing-wax 
 again more rapidly than writing-paper, and so on 
 down to the metals, which cooled the slowest of 
 all. 
 
 Then, having dealt with different substances, 
 the youth set to work to ascertain what effect an 
 alteration in the arrangement of the surface pro- 
 duced in the radiating power of the same sub- 
 stance. Accordingly he tarnished, by means of acid, 
 one of the sides of the polished tin canister he had 
 previously employed, and found, on filling the vessel 
 again with hot water, that the dulled surface parted 
 with its heat quicker than the bright one. After 
 this, he proceeded to roughen another of the sides 
 with some emery paper, and then, on re-filling the 
 vessel, he discovered that the scratched surface 
 cooled at a greater rate than the smooth polished one. 
 
 “ So, then,” said young Humphry to himself, 
 “ not only have different substances various radiat- 
 ing powers for heat, but also a difference in the 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 12.3 
 
 arrangement of the surface of the same substance is 
 attended with a like effect.” 
 
 Still the lad had to examine the result produced 
 by bodies of different densities , and this he did by 
 means of a vessel of cast-iron and one of wrought- 
 iron, when he found that the cast metal parted with 
 its heat quicker than the hammered or wrought 
 metal ; so that it was evident a lighter material was 
 a better radiator of caloric than a heavier one — for 
 the particles of the iron in being wrought had 
 been brought closer together, and the metal thus 
 rendered of greater density. 
 
 This done, Humphry made an entry in his note- 
 book, “ that not only did rough or dull surfaces 
 part with their heat quicker than smooth or bright 
 surfaces, but that light bodies were better radiators 
 than heavy ones.” 
 
 The young experimentalist was overjoyed with 
 the progress he had made, and he would have 
 rambled off into a number of speculations as to the 
 effect which the principles he had discovered must 
 produce in nature (for he saw that the different 
 surfaces of different countries must yield a like 
 result) ; but he was too intent on pursuing the in- 
 vestigations he had undertaken to allow himself, yet 
 awhile, to apply them to the explanation of terres- 
 trial phenomena. Moreover, he had still to learn the 
 different rates of cooling among bodies in the air 
 and in a vacuum. To do this, however, an air-pump 
 
124 
 
 THE WONDERS OF SCIENCE. 
 
 was necessary, and how he was to obtain such an ap- 
 paratus puzzled his ingenuity for a considerable time. 
 
 At length the youth remembered to have seen a 
 large syringe among Mr. Tonkin’s instruments, and 
 having obtained the loan of this, he applied it to a 
 stand, and used it as the pump for extracting the 
 air from the receiver. When the instrument was 
 complete, Humphry found that bodies which took 
 between two and three minutes to cool in the air 
 were as long as five minutes in parting with the 
 same quantity of heat in a vessel from which all the 
 air had been exhausted. So he now perceived, that 
 the same substances gave off their heat twice as 
 quick in the open air as they did in vacuo . 
 
 The next step was to ascertain the different 
 amounts of radiation among different bodies on the 
 earth. For this purpose the boy borrowed as many 
 thermometers as he could procure among his friends 
 in the town ; and early one evening, after the sun 
 had declined, and when the soil was parting with 
 the heat it had received in the course of the day, he 
 proceeded to test, by means of the instruments, the 
 several rates at which the various substances upon 
 the earth were being cooled down. One of the 
 thermometers he suspended in the air four feet above 
 the grass -plat in the garden at the back of the 
 doctor’s house ; another he placed on some wool 
 which he had spread on a raised board ; another he 
 deposited on the surface of the raised board itself ; 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 125 
 
 and a fourth he rested on the grass-plat. Shortly 
 afterwards he proceeded to note the temperatures 
 indicated by the several thermometers in the differ- 
 ent situations, when he found that the one in the 
 air stood at rather more than 60°, while that resting 
 on the wool was at 54°J, and that lying on the 
 board at 57°, whereas the one on the grass -plat 
 marked only 51°. In an hour or two after this, the 
 boy noticed that the blades of grass were suffused 
 with dew, and that the fibres of the wool also were 
 beaded over with little drops of moisture, but to a 
 less extent than the grass, while the surface of the 
 board remained almost dry. 
 
 “ So then,” he said to himself, “ wool is a better 
 radiator than wood , and, cooling quicker, condenses 
 the moisture of the air more rapidly upon it ; but 
 grass again, as the thermometer showed, cooled 
 quicker even than the wool, and therefore collects 
 more dew than either.” 
 
 This induced young Humphry to try another ex- 
 periment, in order to ascertain whether those bodies 
 which cooled most rapidly collected the most dew 
 on their surfaces. Accordingly he placed a piece 
 of bright polished metal and a piece of glass (for the 
 surfaces of these substances were nearly the same) 
 on the gravel-path, and was delighted to perceive 
 that in a short time the glass was covered with 
 moisture while the metal remained perfectly dry. A 
 strip of flannel was then put beside the other two, 
 
126 
 
 THE WONDERS OF SCIENCE. 
 
 and, being a good radiator, it soon became spotted 
 with dew-drops. After this the boy coated the 
 piece of polished metal with lamp-black, and found 
 it then, like the others, capable of condensing the 
 moisture of the air upon its surface. 
 
 “ It is as I expected,” cried the lad ; “ the dew 
 which the ancients imagined to be shed from the 
 stars is simply the condensation of the vapour in 
 the atmosphere upon cold surfaces ; and, conse- 
 quently, those bodies which have the greatest ra- 
 diating power, and so become cold the quickest, are 
 found to have the largest deposition of dew formed 
 upon them, while those which, like polished metals, 
 part with their heat but slowly, and so remain for a 
 long time at the same temperature, have but little 
 moisture condensed upon their surface. The depo- 
 sition of dew,” he went on musing, “ is precisely 
 similar to the condensation of moisture that occurs 
 on the outside of a bottle of very cold water when 
 brought into a warm room. The cold surface of 
 the glass abstracts heat from the vapour in the air 
 of the apartment, and so causes it to be condensed 
 in the form of little watery globules on the surface. 
 In the same manner the earth, parting at night 
 with the heat it has received during the day from 
 the sun, becomes cooler than the atmosphere above 
 it: — for thermometers show, that when the grass 
 is at 51° in the evening, the air only four feet above 
 it is more than 60° — and accordingly the cold sur- 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 127 
 
 face of the blades acts upon the vapour in the atmo- 
 sphere, precisely the same as the outside of the cold 
 bottle does upon the air in a warm room.” 
 
 So pleased was the lad with the insight that his 
 investigations had given him into some of the mys- 
 teries of nature, that he continued his experiments 
 on this subject for many nights ; and in the course 
 of these he found, that not only had different bodies 
 different dew-collecting powers, but that different 
 colours even possessed the same property ; for on 
 exposing a piece of yellow, of green, of red, and of 
 black glass to the night air, he perceived that the 
 moisture appeared first on the yellow glass, then on 
 the green , but that none at all showed itself on 
 either the red or black glasses. 
 
 To his astonishment, however, he at length dis- 
 covered, that when the evenings were cloudy , and 
 there seemed to be a greater quantity of moisture in 
 the atmosphere, the pieces of flannel and glass, and 
 little piles of swan’s-down with which he had studded 
 the gravel-walk, remained unmoistened with dew ; 
 whereas, when the nights were clear and apparently 
 dry> they, one and all, with the exception of the 
 polished metals, became rapidly suffused with mois- 
 ture. This for awhile entirely baffled the boy’s 
 comprehension. “ How came it that more dew was 
 deposited on dry clear nights than on dull damp 
 ones ?” Surely, such being the case, the dew can- 
 not be said to proceed from the vapour in the atmo- 
 
128 
 
 THE WONDERS OF SCIENCE. 
 
 sphere ; for if it does, reasoned Humphry, it is evi- 
 dent that when there is more moisture in the air 
 there should be more dew deposited on the earth. 
 
 At length it struck the boy that, penhaps, the 
 clouds themselves might interfere in some way or 
 other with the result ; so the next fine clear night 
 he strewed the gravel-walk, as before, with frag- 
 ments of such substances as he had already found 
 to be the best collectors of dew ; and then, at the 
 other end of the path, he placed pieces of the same 
 substances under a small awning, which he made out 
 of his pocket-handkerchief, fastened at each corner 
 to a short stick. This he did in order to see what 
 effect would be produced by screening bodies from 
 the sky — since the clouds, he fancied, might act in 
 some such manner. 
 
 On returning to the garden after a short interval, 
 Humphry was rejoiced to find that there was a 
 copious deposition of dew on the pieces of glass and 
 wool that he had left exposed to the sky, while the 
 surfaces of those which were screened by the little 
 awning above them remained perfectly dry. 
 
 “ Yes,” cried the lad, 66 the clouds do act as 
 screens. They give back, perhaps, some of the 
 heat that the earth at night is radiating into space, 
 and so prevent bodies cooling down as rapidly as 
 they otherwise would.” 
 
 However, to satisfy himself that the clouds really 
 did interfere with the radiation of bodies on the 
 
THE WONDERFUL DIFFUSION OF HEAT. 129 
 
 earth, Humphry arranged an apparatus for testing 
 the point. This consisted of a thermometer, the 
 bulb of which was first incased in wool (for that 
 substance he knew to part readily with heat) and 
 afterwards fixed in the focus of a small concave 
 mirror. Then on the next windy night, when the 
 clouds were drifting swiftly across the sky — leaving 
 the heavens occasionally clear, and occasionally hid- 
 ing the light of the stars — the anxious lad turned 
 the mirror towards the blue vault above, and, on 
 doing so, he could hardly repress his glee as he 
 beheld the quicksilver in the tube of the thermo- 
 meter descend and ascend, each time the sky became 
 clear or clouded. Though, by means of another 
 thermometer, he knew the temperature of the sur- 
 rounding atmosphere to be 60°, Humphry neverthe- 
 less found that, when the sky was unclouded , the 
 mercury in the one attached to the mirror indicated 
 only 45°, whilst immediately that a cloud passed 
 over the firmament , and so prevented the bulb from 
 parting with its heat, the quicksilver rose rapidly 
 again to the temperature of the air around. So 
 intensely did Humphry exult in the result of this 
 experiment, that he remained long, watching the 
 thermometer rise and fall, as the clouds swept one 
 after another across the sky. 
 
 The next day, Humphry, now that he had made 
 himself acquainted with the circumstances that 
 
 K 
 
130 
 
 THE WONDERS OF SCIENCE. 
 
 regulated the emission or radiation of heat from 
 bodies, began to turn his attention to the reflexion 
 of it from such substances as impeded the progress 
 of the rays ; “ for,” said he, “ if bodies at an ele- 
 vated temperature have the power of sending out 
 rays of heat in all directions — in the same manner 
 as luminous bodies emit rays of light — it follows that 
 substances opposing the passage of the heat-rays 
 must either absorb them, and so become heated 
 themselves — or they must transmit them and so 
 allow the rays to proceed in their original direction 
 — or else they must reflect them and so bend 
 them into another course.” 
 
 For the study of the reflexion of heat the lad 
 procured two concave mirrors, made of tin-plate 
 and about 1 foot in diameter. These he arranged 
 so as to slide up and down a pillar, to which they 
 were respectively attached. Thus provided, Hum- 
 phry proceeded to place a small “ Florence flask,” 
 filled with hot water, in the focus of one of the 
 mirrors, while in the other focus he arranged a 
 thermometer after this fashion: — 
 
THE WONDERFUL DIFFUSION OF HEAT. 131 
 
 Now, though the mirrors were some feet apart, the 
 mercury in the tube, to the boy’s great delight, rose 
 almost to the heat of the boiling water in the flask. 
 
 After a few moments’ reflection, the lad fancied 
 the effect might perhaps be due to the radiation 
 of the heat from the flask itself, rather than to the 
 reflexion of it from the mirrors. So, to satisfy him- 
 self whether or not such were the case, he placed 
 a sheet of pasteboard immediately in front of the 
 mirror near the thermometer, and thus prevented 
 any rays being reflected from the one to the other. 
 No sooner, however, had he done so than the mer- 
 cury was seen to fall in the tube — even though 
 the source of heat was as near to the thermometer 
 as before ; but directly he removed the pasteboard 
 from between the mirror and the thermometer, the 
 quicksilver rose rapidly again, and stood at the same 
 number of degrees as it previously did. 
 
 Having convinced himself upon this point, he 
 then drew the thermometer away from the focus 
 and nearer to the heated flask, so that, if the effect 
 were due to radiation, the mercury, as it approached 
 the source of heat, should rise higher in the tube. 
 The contrary result, however, was found to ensue ; 
 and it will be seen on reference to the preceding 
 engraving, that by radiation only a few of the heat- 
 rays (which are indicated by the diverging unbroken 
 lines) would fall upon the thermometer, whereas by 
 reflexion a much larger number of such rays become 
 
132 
 
 THE WONDERS OF SCIENCE. 
 
 concentrated upon the bulb in the focus of the opposite 
 mirror — as shown by the dotted lines in the diagram. 
 
 Humphry was now anxious to see whether, by 
 reflexion of the heat-rays, he could ignite combust- 
 ible bodies at a distance ; but for this purpose he 
 changed the situation of the mirrors, arranging 
 them vertically one above the other, instead of 
 horizontally, or each on a level with the other, as 
 before. Then he made 
 a small basket of iron 
 wire, and having filled 
 this with burning char- 
 coal, he suspended it 
 below the upper mir- 
 ror, so that it hung 
 exactly in its focus, 
 whilst above the lower 
 mirror he fixed a small 
 piece of phosphorus, 
 and this was exactly 
 in the focus also. — 
 
 Thus, oi 
 tion of 
 m e n t, 
 the boy 
 was as 
 
 astonished as he was delighted to perceive that the 
 phosphorus was immediately inflamed by the re- 
 flected rays of heat. Some fulminating silver was 
 
THE WONDERFUL DIFFUSION OF HEAT. 133 
 
 then exploded in like manner. After this Hum- 
 phry boiled some water in a flask that he substi- 
 tuted for the piece of phosphorus in the focus of the 
 lower mirror, and finally cooked a chop, by the same 
 means, at some considerable distance from the fire. 
 
 Next, instead of the two mirrors, he rolled up a 
 sheet of bright gilt paper, with the metallic side in- 
 wards, into the form of a long cone or funnel, so that 
 the opening was larger at one end than at the other ; 
 then holding the larger end towards a clear fire, 
 he found the rays of heat were concentrated into 
 a focus at a little distance beyond the smaller end, 
 and there he caused a bit of phosphorus again to 
 inflame, by means of the reflected heat. The sub- 
 joined diagram exhibits the arrangement.* 
 
 Humphry now began to wonder what effect 
 would be produced by a piece of ice placed in the 
 
 * A lucifer match may be conveniently employed for the same 
 purpose, and it will be found that the match, by means of the cone, 
 may be inflamed at a greater distance from the fire than it could 
 possibly be without it. 
 
134 
 
 THE WONDERS OF SCIENCE. 
 
 focus of one of the mirrors ; and he thought for a 
 long time whether the rays of cold would be re- 
 flected from the ice, as those of heat had been from the 
 hot water and the burning charcoal. As the winter 
 had long set in, he found no difficulty in obtaining 
 such a piece as he required from one of the 
 neighbouring ponds, and then arranging the mir- 
 rors as before, he placed it in the focus of one of 
 
 them, while in that of the other he fixed the ther- 
 mometer which he had previously employed. 
 
 To the lad’s astonishment he discovered that the 
 mercury immediately began to fall, and at length 
 stood at 32°, or the freezing point. “ So then!” 
 he cried, “ it is possible to reflect rays of cold 
 as well as those of heat . And yet,” said he to 
 
 himself, after musing for a while, “ is it the ice, 
 after all, that is radiating cold to the thermometer, 
 or the thermometer itself, which, being warmer 
 than the frozen water, is really and truly radiating 
 heat to the ice ? ” If, instead of the thermometer, 
 he had placed a red-hot body in the one focus, while 
 the ice remained in the other, Humphry knew well 
 enough that the warmer body, as it became cool, 
 would be giving off heat to the colder one. “ Why 
 
 then, ” he asked himself, “ should he fancy that the 
 thermometer itself — because it was only a few 
 degrees warmer than the ice — lacked the power of 
 parting with its heat to the colder body, in the same 
 manner as the red-hot charcoal ? ” 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 135 
 
 The lad was soon convinced of his previous 
 fallacy ; and when he saw that the apparently 
 contradictory effect was no anomaly after all, he 
 could hardly refrain from smiling at the simplicity 
 which had led him to believe at first that rays 
 of cold were reflected from the ice to the ther- 
 mometer, instead of the rays of heat being given 
 off by the thermometer to the ice. 
 
 As yet, however, Humphry had experimented 
 concerning the reflexion of heat with mirrors only 
 of polished metal; and one day, when he was re- 
 counting to Mr. Tonkin the curious effects he had 
 produced, the old gentleman asked the lad what he 
 imagined would have been the effect if, instead of 
 metal mirrors, he had used glass ones. 
 
 Humphry answered confidently, that, as the re- 
 sults were due only to the reflexion of the rays 
 from the concave surface, a glass mirror, of course , 
 would have given precisely the same effects as the 
 metal ones. 
 
 “ Try it,” was all the old man said, as he smiled 
 at the positiveness of the boy’s reply. 
 
 Nor was the young experimentalist long in doing 
 so, for he saw by Mr. Tonkin’s manner that some 
 strange difference in the effect would ensue — though 
 for the life of him he could not divine what it was 
 to be. 
 
 Accordingly, at the earliest opportunity, the boy 
 substituted the glass concave mirror, which Mr. 
 
136 
 
 THE WONDERS OF SCIENCE. 
 
 Tonkin had lent him for the purpose, for one of 
 the metal ones which he had previously employed ; 
 then filling the little wire basket with red-hot 
 charcoal, as before, and hanging it in the focus 
 of the upper mirror, he once more suspended a 
 piece of phosphorus in the focus of the lower 
 mirror, which was now of glass instead of metal . 
 To his utter amazement, however, the phosphorus 
 was no longer capable of being inflamed in such a 
 manner. 
 
 It was but the work of a moment to remove the 
 combustible from the focus of the glass mirror, and 
 to place a thermometer there in its stead ; and this 
 soon showed that there was now little , if any , heat 
 reflected. 
 
 “ How wonderful !” cried the startled boy. 
 “ What can be the cause of it ? I’ll arrange the 
 mirrors differently,” he added, “ and see if I can 
 find it out.” 
 
 But no sooner did Humphry put his finger on 
 the glass than he drew it suddenly back, as he 
 exclaimed, “ How hot the lower mirror has become! 
 and I remember when I used the metal one, that 
 I was surprised to find, on removing it, though 
 the heat was sufficient to boil water and ignite 
 bodies in its focus, the metal surface of the mirror 
 itself was scarcely warmed. But now that glass is 
 used,” he went on, “ the mirror itself is rendered 
 hot , while in the focus of it there is scarcely any 
 

 
 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 137 
 
 perceptible increase of temperature . So, then,” 
 
 lie added, “ the glass absorbs the heat-rays, and 
 therefore does not reflect them, while the metal 
 on the other hand reflects , because it does not 
 absorb them. Still it’s very strange,” mused Hum- 
 phry, as he proceeded to blacken a small card, 
 “ for the glass mirror must reflect the light of the 
 fire, though it absorbs the heat from it. I’ll try 
 whether such is the case or not.” 
 
 The card was then placed in the focus, and a 
 bright spot of light was seen shining like silver 
 in the centre of the blackened surface. 
 
 “ Yes,” cried the lad, “ it reflects the light, but 
 not the heat of the fire. How strange ! I wonder 
 whether the same effect would be produced by the 
 sun’s rays ! ” 
 
 Accordingly the next day, when the sun was 
 shining brightly, Humphry arranged the mirror in 
 the garden, so that the beams might be concen- 
 trated in its focus ; and then, to his greater asto- 
 nishment, he found that he could inflame com- 
 bustibles by the solar heat with the glass mirror, 
 in the same manner as he had previously done by 
 artificial heat with the metal ones. 
 
 “ The light and heat of the sun, then,” said 
 Humphry, as he stood watching the white fumes 
 of the burning phosphorus rise in the air, “ are 
 capable of being reflected by glass, whereas the 
 light only of an artificial fire can be concentrated 
 
138 
 
 THE WONDERS OF SCIENCE. 
 
 into a focus by it — the heat in the latter cas8 
 being absorbed.” 
 
 The metal mirror, likewise, was found to possess 
 the power of reflecting both the solar light and heat, 
 in the same manner as it had been before made to 
 reflect both the light and heat of an artificial fire. 
 
 The experiment with the glass mirror, however, 
 clearly showed that solar heat differed in some way 
 or other from terrestrial heat ; but how , was a 
 source of continual wonder to the lad. 
 
 From the reflexion of heat, Humphry proceeded 
 to the transmission of it. 
 
 Light passes readily through certain substances, 
 which are therefore said to be transparent , while 
 others impede the progress of the beams, and are 
 consequently called opaque . “ Is there, then,” 
 
 mused the boy, “ such a property as transparence 
 and opacity for heat , as well as light, among bodies ? 
 Are some substances pellucid , as it were, to heat 
 like they are to light ? and are some as imperme- 
 able to the one as they are to the other ? 
 
 The lad knew well that the heat of the sun was 
 capable of being transmitted through glass as well 
 as its light, for he had often concentrated the 
 solar beams by means of a magnifying or “ burn- 
 ing” lens, as it is called: glass, therefore, was 
 transparent to the solar heat as well as light ; but 
 was it so to the rays of artificial heat ? 
 
THE WONDERFUL DIFFUSION OF HEAT. 139 
 
 To ascertain this, Humphry borrowed old Dr. 
 Tonkin’s large reading lens, and held it before the 
 fire so that the focus fell upon the bulb of a ther- 
 mometer. But though the light of the burning 
 coals was seen concentrated into a bright spot upon 
 the bulb, still the mercury in the tube gave no in- 
 dications of any increase of temperature. The lens, 
 however, which was scarcely warmed when the sun’s 
 rays passed through it, became greatly heated when 
 the rays of the artificial fire were made to fall upon 
 it — thus showing, that while it transmitted the solar 
 heat it absorbed the terrestrial. 
 
 It was evident, therefore, that though the heat of 
 the sun has the power of passing freely through 
 glass, artificial heat , on the other hand, is com- 
 pletely stopped by it. 
 
 Humphry then thought he should like to try the 
 effect of a piece of black glass, for this would be 
 perfectly opaque to light, and he longed much to see 
 whether it would be equally impermeable to heat. 
 On holding a square piece before the fire, the boy 
 was surprised to perceive the thermometer he had 
 arranged behind it rise rapidly, thus showing that 
 though black glass was in- transparent to light , it was 
 by no means opaque to heat That the quicksilver 
 was made to mount in the tube solely by the influence 
 of the heat-rays which traversed the black glass — 
 and not by any indirect radiation from the fire — 
 Humphry assured himself, by placing a piece of white 
 
140 
 
 THE WONDERS OF SCIENCE. 
 
 glass, of' the same size and thickness as the black one, 
 before the thermometer : the quicksilver, however, 
 was immediately seen to fall. “ How marvellous is 
 this !” he exclaimed. “ Light and heat, then, are 
 capable of being separated one from the other 
 and there are bodies in nature which, like white 
 glass, are transparent to light, but opaque to heat ; 
 while there are others, like black glass, that allow 
 the heat -rays to pass through them, though they 
 are incapable of being traversed by the luminous 
 ones.” 
 
 The boy was so full of the new truth that had 
 thus become impressed upon his mind, that he 
 hurried off to Mr. Tonkin to confer with him on the 
 result. From him Humphry learnt that there 
 were other substances, besides glass, that gave 
 equally curious effects, — the most striking of these, 
 the old gentleman told the boy, were alum and rock- 
 salt % for though both were transparent to light, they 
 had by no means the same power of transmitting heat ; 
 for it would be found, that while a small plate of 
 rock-salt allowed the rays of heat to pass almost 
 freely through it, a similar plate of alum was nearly 
 impermeable to them. 
 
 The young philosopher was not long in trying 
 the experiment. Having procured two such plates 
 as Mr. Tonkin had advised, he used them as small 
 screens in front of the fire, and found that a ther- 
 mometer behind the rock-salt rose rapidly; whereas, 
 
THE WONDERFUL DIFFUSION OF HEAT. 141 
 
 behind the alum, it was scarcely affected, for the 
 heat was nearly all stopped by it. 
 
 The possibility of separating heat from light 
 made a powerful impression upon the ardent boy, 
 and he wondered whether he could arrive at the 
 same result with the solar beams as he had with 
 the rays of an artificial fire. For a long time he 
 pondered over the matter, and conceived and tried 
 a number of fruitless experiments in connexion 
 with it. 
 
 At length, however, he remembered to have read 
 somewhere, that by means of a glass prism the 
 beam of white light proceeding from the sun might 
 be separated into all the colours of the rainbow. 
 
 Accordingly he set to work to repeat the experi- 
 ment. Having darkened his room he made a hole 
 in the window-shutter, and placed behind it a glass 
 prism, with one of the sharp edges downwards and 
 one of the flat sides uppermost, as shown in the 
 annexed illustration : — 
 
 Immediately that the arrangement was complete, and 
 
142 
 
 THE WONDERS OF SCIENCE. 
 
 the beam from without fell on the glass within, the 
 wall on the opposite side was iridescent with a strip 
 of variegated light, as if a slice of a bright rain- 
 bow were clinging to it. The lower end of the 
 luminous band was a rich warm red, and this 
 passed, by a tint of orange, into a bright yellow, 
 which again died away, by deepening hues of green, 
 into a narrow strip of dark blue, while, at the 
 upper end, the indigo tint became warmed into a 
 brilliant edging of violet. 
 
 When the rapture of the boy on first beholding 
 the sight had, in a measure, subsided, he proceeded, 
 by means of a thermometer, to ascertain the tem- 
 perature of the several rays. First he tried the 
 upper end of the spectrum, and found that in the 
 blue ray the mercury marked 56°. Then passing 
 downwards Humphry was overjoyed to see the 
 quicksilver mount as he proceeded towards the 
 middle, where, in the yellow ray, the instrument in- 
 dicated a temperature of 62°, i. e. 6° higher than in 
 the blue ; while at the lower end — at the extremity 
 of the red ray — the temperature was found to be as 
 high as 79°, i. e . 17° higher than it was in the yellow. 
 
 There was then, altogether, as much as 33° dif- 
 ference between the heat at the extreme ends of the 
 luminous band — the red ray being upwards of half 
 as hot again as the blue one — so that light and heat 
 were capable of being separated even in the solar 
 beams themselves; for the yellow contained the 
 
THE WONDERFUL DIFFUSION OF HEAT. 143 
 
 most light of all, and yet it was 17 ° colder than the 
 extreme verge of the red ray, where there was only 
 a faint luminous blush to be perceived. 
 
 The next step was to ascertain the circumstances 
 regulating the reception or absorption of heat. 
 
 Humphry had now investigated the laws which 
 governed the radiation or emission of the rays of 
 heat from bodies at an elevated temperature. He 
 had ascertained that these rays not only emanated 
 from heated substances at different rates, and so 
 caused them to cool down more or less rapidly, but 
 that — though their tendency was to proceed, like the 
 rays of light, in a straight line — they were capable 
 of being reflected or bent back by certain bodies 
 opposing their progress, and that in such cases the 
 reflecting bodies themselves did not become heated 
 by them. Other bodies, again, he had found to have 
 the power of transmitting the rays of heat, that 
 is to say, of allowing them to pass through their 
 substance rather than reflecting or driving them bach 
 from their surface ; and such transmitting bodies, 
 moreover, were likewise scarcely warmed by the 
 heat that traversed them. Now he was about to 
 investigate the conditions that determined the ab- 
 sorption of the heat-rays, by bodies upon which 
 they fell after being given off by radiation from 
 others of a higher temperature. 
 
 The lad’s first experiment upon this subject was 
 
144 
 
 THE WONDERS OF SCIENCE. 
 
 to blacken the surface of one of the metal mirrors 
 that he had previously found to reflect the heat, 
 without being itself warmed in so doing. 
 
 The result proved to be as Humphry had antici- 
 pated. The mirror no longer had the power of 
 concentrating the heat in a focus, at a short distance 
 in front of it: for now, instead of reflecting the rays 
 and remaining cool as before, it absorbed all the 
 heat that fell upon it, and became itself warmed by 
 the neighbouring radiator. 
 
 The same effect ensued when the surface of the 
 mirror was whitened with chalk, and the same 
 again when it was roughened, or scratched, with 
 emery paper: so that rough and dull bodies proved 
 to be better absorbers of heat — even as they were 
 better radiators — than bright or polished ones. 
 
 Hence there appeared to be some connexion 
 between the radiating and absorbing powers of 
 different substances — those which cool the quickest 
 seeming to be capable, also, of being heated in the 
 shortest time. 
 
 To test this the lad placed a blackened and a 
 bright-polished vessel in front of the fire, and found 
 that the thermometer in the black vessel rose much 
 more rapidly than did that in the bright one. 
 
 Humphry then availed himself of these two 
 vessels as a means of testing the relation between 
 the absorbing and radiating powers of black and 
 bright-polished surfaces. Into the mouths of the 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 145 
 
 black and the bright tin vessel he inserted a ther- 
 mometer, and then placed between them one of the 
 square canisters he had previously employed, and 
 which, it will be remembered, had one of its sides 
 bright, while the opposite one was coated with 
 lamp-black. 
 
 Having filled the middle canister with boiling- 
 hot water, he proceeded first to note the radiating 
 and absorbing effects when the different surfaces 
 were opposed to each other. On arranging the 
 middle canister so that its black side was turned 
 towards the polished vessel at one end, and its 
 polished side to the blackened vessel at the other 
 end, there was no effect produced upon either of the 
 thermometers; for then the opposite powers of the 
 different surfaces exactly balanced each other. 
 When, however, the apparatus was so adjusted that 
 similar surfaces were opposed — that is to say, so 
 that the blackened side of the canister in the 
 middle was turned towards the black vessel, and 
 the bright - polished side to the bright - polished 
 vessel — the thermometer in the black vessel im- 
 mediately indicated a great excess of heat; for 
 then not only was there a good radiator opposed 
 to a good absorber , but, on the other side, the two 
 bright surfaces were facing each other— that is, 
 the bad radiator was turned towards the bad 
 absorber — so that even the little heat which was 
 given off from the polished side of the canister 
 
 L 
 
146 
 
 THE WONDERS OF SCIENCE. 
 
 was driven back again to it by the surface of the 
 neighbouring bright vessel. Hence everything 
 favoured the radiation and absorption of the heat 
 on the one side, where black was opposed to black, 
 and prevetited it on the other, where metal was 
 facing metal; and thus the great elevation of the 
 thermometer was accounted for. 
 
 As it was now winter time and the snow lay 
 thick upon the earth, Humphry availed himself 
 of the circumstance to test the absorbing powers 
 of different colours . For this purpose he took a 
 number of pieces of different coloured cloths, and 
 placing them at mid-day upon the snow, so that the 
 sun’s rays could fall directly upon them, he found 
 that the dark colours sank the deepest into the 
 frozen mass beneath, while the lighter hues pro- 
 duced scarcely any thawing effect, and the white 
 remained utterly inactive. 
 
 The same result was obtained by means of co- 
 loured glasses; for against a window-pane that was 
 covered with hoar-frost the lad placed some pieces 
 of black, red, green, and yellow glass, and the con- 
 sequence was, that the ice opposite to the black and 
 red pieces was melted long before any thawing 
 effect was visible upon the frozen film screened 
 by the other colours. 
 
 When the weather grew warm Humphry ob- 
 tained another very curious illustration of the 
 power of black substances to absorb the heat of 
 
THE WONDERFUL DIFFUSION OF HEAT. 147 
 
 the sun’s rays. Having filled a glass tube with 
 spirits of wine, he placed it in the focus of a lens, 
 and found that the solar heat traversed the trans- 
 parent liquid without warming it. On immersing 
 a small piece of charcoal, however, in the alcohol, 
 so great was the absorptive power of the black 
 surface that the fluid immediately began to boil. 
 By the same means, too, he succeeded in raising 
 the temperature of water to the boiling point. 
 This showed that water, as well as spirits of wine, 
 was a good transmitter and bad absorber of heat ; 
 that is to say, that the rays passed freely through 
 each without warming either, unless some sub- 
 stance were immersed in the liquid in order to 
 detain and absorb their heat. 
 
 Air , on the other hand, the boy knew to have 
 little or no heat-absorbing power ; for the rays 
 emitted by a distant hot body traversed the atmo- 
 sphere without sensibly raising its temperature. 
 He had read, too, that philosophers had calculated 
 that only one-fifth of the solar heat was absorbed 
 in passing through 1000 feet of the air, and that 
 but one -third of the entire heat of the sun was 
 taken up by the passage of the beams through the 
 whole atmosphere. 
 
 Humphry, moreover, sought to discover whether 
 the sun’s heat, reflected from a mirror, would pro- 
 duce the same effect as the direct solar beams. 
 Accordingly, before the winter passed away, he 
 
148 
 
 THE WONDERS OF SCIENCE. 
 
 placed two pieces of blackened card upon the snow, 
 at a considerable distance apart. One of these he 
 left exposed to the direct rajs of the sun, while upon 
 the other he caused the sun-beams to fall indirectly , 
 by reflecting them from a polished metal surface. 
 The black card that was submitted to the direct 
 solar beams sank, after a little time, deep into the 
 snow, while the frozen mass around — though the 
 beams fell full upon it — was but slightly thawed. 
 With the black card, however, upon which the sun’s 
 rajs were reflected , a precisely opposite result ensued. 
 In that case the surrounding snow itself was the first 
 to melt, while the blackened surface seemed to have 
 been deprived of its power of absorbing heat, and 
 remained high on the unthawed pile beneath it. 
 
 Further, Humphry noticed that the snow which 
 lay near the trunks of trees, or wooden posts, 
 melted much sooner than that which was at a 
 distance from them, and that the thawing always 
 commenced at the side facing the sun. Hence it 
 was evident that the solar heat, after being either 
 reflected or radiated from bodies on the earth, and 
 so made to fall indirectly upon other bodies, was 
 rendered capable of being absorbed by substances 
 which, like snow, had but little or no power of 
 being warmed by it directly . 
 
 Why this should be, or what alteration the solar 
 rays underwent in impinging upon terrestrial 
 bodies, so that substances which before absorbed 
 
THE WONDERFUL DIFFUSION OF HEAT. 149 
 
 the sun’s heat with difficulty became afterwards 
 more easily warmed by it, was more than Hum- 
 phry’s philosophy could explain — though it cost 
 him many a day’s hard thinking in trying to 
 account for the result. 
 
 Having now investigated the conditions which 
 governed the diffusion of heat from a distant point, 
 Humphry next proceeded to inquire into the cir- 
 cumstances which regulated the communication of 
 heat to bodies in contact with others at an elevated 
 temperature. 
 
 This constitutes what is called the conduction of 
 caloric, and occurs between different bodies, or 
 parts of the same body, immediately adjoining 
 each other. The communication of heat by con- 
 duction is a slow process compared with that of 
 radiation , which is, probably, as rapid as the diffu- 
 sion of light itself. Philosophers have calculated, 
 that even if the crust of the earth were made of 
 cast-iron (which is a much better conductor than 
 rocks and stones), it would take myriads of years 
 to transfer the heat from a depth of 150 miles 
 below the surface to the surface itself ; whereas by 
 radiation the solar heat travels from the sun to us 
 in 8^- minutes. 
 
 The laws which regulate the communication of 
 caloric to distant objects are similar to those which 
 would ensue if the heat really consisted of so many 
 
150 
 
 THE WONDERS OF SCIENCE. 
 
 hot particles darted out from the heated body in all 
 directions ; and colder bodies placed in the neigh- 
 bourhood of heated ones, either become hot in the 
 same manner as they would if such particles were 
 positively absorbed by them, and entered into their 
 substance ; or they reflect the heat to other bodies, 
 while they themselves are unwarmed by it — as if 
 (according to the hypothesis) the caloric particles 
 were elastic, and had the power of bounding off from 
 smooth surfaces interfering with their progress ; or 
 else they transmit the heat rays, as if the imaginary 
 particles of caloric were capable of freely traversing 
 certain substances, and that, also, without sensibly 
 raising the temperature of the permeated mass. 
 
 But all bodies, or parts of bodies, which are in 
 immediate contact with some other at a higher 
 temperature, become themselves warmed ; not by 
 rays thrown out from the heated mass, but by con- 
 ducting or diffusing the heat from one point to 
 another, and so disseminating it ultimately through- 
 out their whole substance. 
 
 Humphry was thus particular in impressing upon 
 his mind the precise difference between the radi- 
 ation and conduction of caloric before entering upon 
 the study of the latter process ; for he knew that 
 without clear and distinct views upon the subject 
 it was impossible for him to arrive at any absolute 
 knowledge. 
 
 To illustrate the gradual progress of heat by 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 151 
 
 conduction , the lad took a square bar of iron, about 
 20 inches long, and he attached to the under side 
 of it (by means of a little wax) 10 small wooden 
 balls, so that they were about 2 inches apart from 
 each other. Then he heated one end of the bar in 
 the flame of a lamp, and found that the balls fell 
 from under it ^ 
 
 ■■ v — ¥ ■■■■ ■ i u .... g , — e . 
 
 one ajter an- 
 other, as the 
 heat found its 
 way along the metal and melted the wax below. 
 The arrangement of this simple and instructive 
 experiment is here shown. 
 
 The next step was to learn the different con- 
 ducting powers of different substances. For 
 this purpose Humphry had several small metal 
 cones made, all of the same size ; one of these 
 
 was of copper, another 
 of iron, a third of zinc, 
 a fourth of tin, a fifth 
 of lead, a sixth of 
 marble, and a seventh 
 of brick. Then having 
 tipped each of them 
 with a small piece of 
 wax, he stood them, all 
 a short distance apart 
 from each other, on 
 the metal plate at the top of the iron stove by 
 
152 
 
 THE WONDERS OF SCIENCE. 
 
 which Mr. Borlase’s surgery was heated. The 
 result was, that the wax at the top of the copper 
 cone was the first to melt. Some little time after- 
 wards, that at the apex of the iron began to liquefy; 
 and soon after the iron, that upon the zinc was 
 rendered fluid; while, shortly following the zinc, 
 the wax on the tin commenced trickling down the 
 sides. A short interval elapsed, and then the 
 cerate at the top of the lead became fluid. Again 
 a lapse of a few moments occurred, after which the 
 wax with which the marble cone was tipped began 
 to flow ; and, last of all, that upon the piece of 
 brick was liquefied. 
 
 The different conducting powers for heat among 
 the several substances employed were thus made 
 evident. The metals were more capable than either 
 marble or brick of diffusing the caloric from one 
 part of them to another ; while among the metallic 
 substances themselves copper was proved to be a 
 much better conductor than iron ; iron, again, a little 
 better conductor than zinc ; and zinc, too, slightly 
 better than tin. Lead, on the other hand, was the 
 worst metallic conductor of all. 
 
 The limited means of the young experimentalist, 
 however (for Humphry was obliged to seek Mr. 
 Tonkin’s assistance for any particular apparatus 
 he required), did not admit of his testing the con- 
 ducting powers of either gold or silver. But had 
 he done so, he would have found that the precious 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 153 
 
 metals were much better conductors than any other 
 — gold being the best of all, and silver only a little 
 inferior to it. Platinum , however, was a striking 
 exception, its heat-conducting power being only a 
 little superior to that of iron. 
 
 Humphry after this sought to discover what 
 would be the effect if he placed a good conducting 
 metal in connexion with a bad one. For this 
 purpose he employed a short curved bar of copper ; 
 and having heated it, he set it across the top of 
 a small leaden pillar to cool, thus : — 
 when, to his utter astonishment, a 
 series of musical sounds were given 
 forth as the copper cooled, the tones now rising 
 and now falling like those of an H^olian harp. 
 
 By the same means as Humphry had employed 
 for testing the conducting powers of the metals, 
 he ascertained that wood was a very bad con- 
 ductor of heat, and that the lightest woods were 
 the worst. Charcoal , too, he found to have but 
 
 little power of diffusing the heat from one part of 
 it to another. This explained to the boy the 
 reason why a piece of charcoal, red-hot at one end, 
 may be held — at a short distance even from the 
 heated part — without burning the fingers. 
 
 Humphry now set to work to raise to a con- 
 siderable temperature several pieces of such sub- 
 stances as he had ascertained to be good and bad 
 conductors, so that he might learn what effect they 
 
154 
 
 THE WONDERS OF SCIENCE. 
 
 respectively produced upon the touch when highly 
 heated. As he had anticipated, the bad conductors 
 — such as the wood and brick — could be handled 
 without pain, whereas the good conductors — like 
 the metals — burnt the fingers immediately they 
 were brought into contact with them. 
 
 Pursuing this result, the lad, eager to display 
 his knowledge to the servant of the house, took 
 the boiling kettle from the kitchen fire, and, to the 
 amazement of the maid, allowed the sooty bottom 
 of it to rest upon his palm ; for the crust of char- 
 coal with which (by long usage) the vessel had 
 become coated underneath — being a non-conductor 
 — prevented the heat of the boiling water within 
 being communicated to the hand.* 
 
 On recounting to Mr. Borlase the experiments 
 he had performed concerning the conduction of 
 heat, Humphry was informed by that gentleman 
 that it was painful to touch good conductors like 
 the metals when they were heated about 120°. 
 Air, however, he told the boy, might have its 
 temperature raised even to 300°, without pro- 
 ducing any sense of burning ; adding, that some 
 eminent sculptors had large ovens in connexion 
 with their studios, for drying the moulds they 
 
 * Young gentlemen of an experimental turn are cautioned 
 against attempting the same feat; for, should there be the least 
 part of the metal, at the bottom of the kettle, left unprotected by 
 the soot, they will assuredly experience considerable pain. 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 155 
 
 employed in bronze castings ; and though these 
 places were often heated far above the boiling 
 point of water, the workmen entered, and remained 
 there for some minutes without much incon- 
 venience ; and even persons unused to such high 
 temperatures might walk in and out of the ovens 
 with impunity, though to such any attempt to 
 remain occasioned a difficulty in breathing and 
 a painful sensation about the eyes. It was found 
 necessary, however, under such circumstances, to 
 carefully avoid the contact of any good conductor ; 
 for if, while in the heated oven, a piece of metal 
 were touched, it would inevitably burn — even the 
 coins in the pocket were sufficient to produce in- 
 tense pain. “ A story is told,” he continued, “ of 
 a person who once, inadvertently, entered such a 
 place with his spectacles on, and these, being 
 mounted in silver, soon blistered the parts of his 
 face with which they were in contact. On the 
 other hand,” proceeded the surgeon, “it has been 
 found that in high northern latitudes, where the 
 cold is sometimes sufficiently intense to freeze mer- 
 cury — though this requires the temperature to be 72 ° 
 below that required to freeze water — yet even such 
 excessive cold may be borne without uneasiness, 
 provided the air be tranquil, and the persons well 
 clothed in good non-conductors, such as wool and 
 fur. If, however, metallic substances be touched 
 at this low temperature, a sensation like that of 
 
15G 
 
 THE WONDERS OF SCIENCE. 
 
 burning is experienced, and the part quickly be- 
 comes blistered. “ The reason of this,” the doctor 
 concluded, “ is, that the heat, being as it were free 
 to move in all those substances which are, like the 
 metals, good conductors of it, is readily commu- 
 nicated to us by such substances when at a higher 
 temperature than ourselves, while our heat is as 
 readily abstracted by them when they are colder 
 than we are. Hence good conductors, like metals, 
 always feel colder to the touch than bad con- 
 ductors, like wood or fur — even though these latter 
 bodies can be shown by the thermometer to be of 
 the same temperature as the others.” 
 
 Humphry’s conversation with the doctor induced 
 him to try another experiment, illustrative of the 
 conducting power of wood and metal. He took a 
 small rod of polished brass, about a foot in length, 
 and stretching a strip of writing-paper tightly over 
 it at one end, he tried to burn the paper in the 
 flame of a lamp, but discovered that it was impos- 
 sible even to scorch it ; for the heat, as soon as 
 applied, was conducted away so rapidly along the 
 metal, that it prevented the temperature of the 
 paper being raised sufficiently to char it. On sub- 
 stituting, however, a smooth piece of wood for the 
 brass rod, he found that the paper stretched over 
 the end of it soon began to scorch in the flame, and 
 that the wood itself shortly became ignited in con- 
 sequence of its bad conducting power, which, op- 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 157 
 
 posing the diffusion of the heat along it, concen- 
 trated the effects upon the spot to which the flame 
 was applied. 
 
 After this, the boy began to turn his attention 
 to the conducting powers of liquids , rather than 
 solids , with which he had previously dealt. 
 
 That liquids are very imperfect conductors of 
 heat, Humphry made out in the following manner : 
 He filled a tumbler with water, and in this he 
 placed a piece of “ fusible alloy,” which is a com- 
 position of metals melting at a temperature below 
 boiling heat. Then a thin copper basin was made 
 to float on the surface ; and into this he put some 
 pieces of red-hot charcoal ; so that, after a time, 
 the stratum of water at the top of the tumbler 
 began to boil ; but, even though the upper part of 
 the liquid was at boiling-point, 
 so slight was the power of the 
 water to conduct the heat from 
 one part of it to another, that the 
 stick of alloy, which reached 
 within an inch of the top, re- 
 mained wholly unmelted by it. 
 
 The same effect was found to ensue with heated 
 oil , though this the lad tried in a somewhat dif- 
 ferent manner. In a thin glass tube a small quan- 
 tity of water was frozen by plunging it into a mix- 
 ture of salt and snow. Then, upon the lump of ice 
 at the bottom a small quantity of oil was poured ; 
 
258 
 
 THE WONDERS OF SCIENCE. 
 
 and, lastly, upon the oil some spirits of wine was 
 made to float. The tube was 
 now held over the chimney of 
 a lamp, and the spirit made 
 to boil until the whole was 
 evaporated, when, on plunging 
 a thermometer into the oil, it 
 was found to be but slightly 
 heated, while the ice itself had 
 undergone no change, but remained still solid at the 
 lower part of the tube. 
 
 Next, in due order, came the conduction of heat 
 by gases and vapours; and of this Humphry ob- 
 tained a remarkable illustration in a fact which he 
 learnt of the engineer at the Wherry Mine, who 
 told the lad that high-pressure steam did not burn, 
 though its temperature was some hundred degrees 
 above that of steam at a low pressure. The scald- 
 ing effect of the vapour at a low pressure, the man 
 informed the youth, arose from the small particles 
 of hot water that were diffused throughout it, and 
 which, indeed, rendered it visible in the air ; 
 whereas in high-pressure steam no such watery 
 particles existed, and the vapour was consequently 
 not only imperceptible to the sight, but, being a bad 
 conductor of heat, it had no more power to burn 
 than so much hot air. 
 
 Again, that gases , in a state of combustion, are 
 bad conductors of heat, Humphry was aware, from 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 159 
 
 having repeatedly passed his finger through the flame 
 of a spirit-lamp without burning it, and yet the tem- 
 perature of such a flame might be shown to be many 
 hundred degrees beyond that of a piece of red-hot 
 metal. Air, again, he knew to have little or no 
 conducting power; and he had heard from Mr. 
 Tonkin that in Russia and other cold countries 
 double windows, with a stratum of air between 
 them, were used to prevent the heat of the apart- 
 ment being carried off. So, again, in furnaces, 
 double walls with a stratum of confined air in the 
 middle are employed to stop the egress of heat ; 
 even as in ice-houses the same means are adopted 
 to stay the ingress of it. 
 
 The diffusion of heat by the process of conduc- 
 tion, however, generally occurs among solid bodies, 
 in which the particles are more or less firmly 
 united ; but liquids and gases (where the particles, 
 owing to the want of cohesion among them, are 
 free to move) mostly became warmed by a very 
 different process : that is to say, the heat applied to 
 them is spread from one part to another, — not by 
 being propagated, as in solids, from one fixed par- 
 ticle to that which is next to it — but by the motion 
 or circulation of the heated particles themselves, so 
 that each in its turn receives a portion of the heat 
 applied, and then giving place to another particle, 
 the whole mass ultimately becomes raised to one uni- 
 
160 
 
 THE WONDERS OF SCIENCE. 
 
 form temperature by the direct agency of the radiant 
 body, rather than by the indirect process of trans- 
 ference from atom to atom along the entire sub- 
 stance. The one process is termed the conduction 
 of heat, the other the convection of it ; and while 
 the former prevails among the cohering particles of 
 solid bodies, the latter generally obtains among fluids 
 whose atoms are free to move . 
 
 In order to render visible this same circulation of 
 the particles of fluids while in a heated state, Hum- 
 phry bruised in a mortar a small piece of amber, 
 and then having filled a glass tube with 
 water, he threw in a few pinches of 
 the powder, which, being nearly of the 
 same specific gravity as the liquid, 
 neither sank nor floated in it. Then 
 applying a gentle heat to the centre of 
 the bottom of the tube, the boy saw, by 
 means of the amber-dust suspended in 
 the fluid, that currents immediately 
 began to ascend in the middle of the 
 water, and to descend in it at the sides 
 of the vessel — in the direction of the 
 darts in the annexed engraving. 
 
 If, however, he heated the sides of the tube, 
 the currents were found to take a contrary direc- 
 tion, going upwards at the sides and downwards 
 in the centre. 
 
 On continuing the heat, Humphry perceived the 
 
THE WONDERFUL DIFFUSION OF HEAT. 1C1 
 
 currents to become more and more rapid, till the 
 water boiled, and when the whole of the liquid 
 had acquired an uniform temperature, he observed 
 that they ceased altogether. He then endeavoured 
 to ascertain if it were possible to produce these 
 currents in a liquid by heating it at the top, but 
 the boy discovered, on applying a 
 spirit-lamp to the upper part of the 
 tube, thus, — that though the top of 
 the water was made to boil, and the 
 amber- dust there throw-n into rapid 
 circulation, the particles at the bottom remained 
 unmoved, the fluid below being undisturbed and 
 cold. 
 
 The reason of this was almost self-evident. The 
 warm water was lighter than the cold, and there- 
 fore rose to the top immediately it became heated, 
 
 , while the cooler and heavier portions descended to 
 occupy its place. Hence, in heating the tube at 
 the bottom the current was observed to go upwards 
 in the middle and downwards at the sides, these 
 being kept comparatively cool by the action of the 
 external air. 
 
 Pursuing this subject, Humphry took a large 
 and a small Florence flask, and into the mouth of 
 the large one he fitted two long bent glass tubes, 
 by means of a perforated cork and cement. These, 
 together with the large flask, were filled with water 
 and then made to dip into the open mouth of 
 
 M 
 
162 
 
 THE WONDERS OF SCIENCE. 
 
 the smaller flask, which 
 was likewise filled with 
 water, but tinged a deep 
 blue with indigo. One 
 of the tubes was ar- 
 ranged so as to dip only about half an inch 
 below the surface of the blue liquid, while 
 the other descended nearly to the bottom 
 of it, and was slightly curved upwards at 
 its extremity. The arrangement will be 
 readily understood by reference to the 
 annexed engraving. On applying the 
 flame of a spirit-lamp to the lower flask, 
 the blue liquid was seen to ascend by the 
 tube on the left side ; then reaching the 
 large flask at the top, it there circu- 
 lated through it, in the direction of the 
 darts, and descended by the other tube, 
 back again to the small flask at the 
 bottom. Thus a perfect circulation was 
 seen to be kept up, and the heat, by means, 
 of convection , carried from one flask to 
 the other. 
 
 After this Humphry sought for some 
 means of rendering the currents of heated 
 air visible in the same manner. For such 
 purpose he took a large glass jar, having 
 a wide opening at the bottom and a narrow 
 one at the top. Into the upper aperture 
 
THE WONDERFUL DIFFUSION OF HEAT. 
 
 163 
 
 he inserted a long lamp-glass, and down this he 
 placed a diaphragm of card, so as to divide the glass 
 chimney into two channels. Then the lad procured 
 a shallow pan, and having poured a little water into 
 it, he set a piece of lighted candle in it and covered 
 it over with the jar and chimney, so that when the 
 whole was duly arranged it appeared as here shown. 
 Then having lighted 
 a piece of brown 
 paper and blown it 
 out again, he held 
 the smouldering end 
 over the chimney, 
 and saw, by the 
 curling of the smoke 
 from the paper, that 
 the heated air from 
 within was ascend- 
 ing the lamp - glass 
 by one side of the 
 diaphragm, and de- 
 scendinghj the other, 
 in the direction of the 
 arrows in the illustration ; whereas, when the card- 
 board partition was removed from the chimney, 
 the currents ceased , and the light was soon extin- 
 guished. 
 
 The boy applied the same simple means, likewise, 
 to learn the direction of the currents of air on open- 
 ing the door of a heated apartment, and found by, 
 
364 
 
 THE WONDERS OF SCIENCE. 
 
 the smoke from a piece of smouldering paper, that 
 at the upper part of the door the heated air from 
 within was rushing outivards , and at the lower part 
 die cold air from without was setting inwards , 
 whilst at the middle scarcely any draught, one way 
 or the other, was perceptible. 
 
 This naturally turned the boy’s attention to the 
 subject of the wind, which appeared to him to be 
 merely a vast current set up in the atmosphere by 
 the heating power of the sun’s rays. He had 
 noticed, too, that, shortly after sunrise, a breeze fre- 
 quently sprang up at sea and blew towards the land, 
 increasing as the day advanced, and declining and 
 ultimately expiring at about sunset ; whilst in the 
 evening, after sundown, a wind often arose in the 
 opposite direction — namely, from the land towards 
 the sea — and lasted the whole of the night, ceasing 
 only with the reappearance of the sun. 
 
 Humphry was therefore anxious to discover some 
 experimental means of reproducing these effects on 
 a small scale. 
 
 Having procured a large shallow milk-pan, he 
 filled it with cold water, and then took a metal 
 “ hot-water plate,” and having poured some boiling 
 water into this, he set it in the middle of the pan, 
 saying to himself as he did so, “ the cold water 
 there, in the outer vessel, represents the ocean, 
 while the heated metal plate in the centre stands for 
 an island warmed by the rays of the sun ; for the 
 land, being a better absorber of heat than the sea, 
 
THE WONDERFUL DIFFUSION OF HEAT. 165 
 
 will have its temperature raised some degrees higher 
 than the water in the course of the day.” 
 
 This done, the eager boy proceeded, by means of 
 the smoke from a piece of smouldering paper as 
 before, to discover the direction of the currents that 
 would be set up in the air under such circumstances. 
 As he held the smoking paper at the edge of the 
 pan, Humphry was delighted to see the white fumes 
 drawn towards the hot plate in the middle, or, in 
 other words, from the miniature ocean towards the 
 mimic island encompassed by it ; and this he knew 
 was precisely the current that was found to prevail 
 throughout the day in tropical countries. 
 
 Then, to impress the phenomena firmly upon his 
 mind, the boy drew in his note-book the annexed 
 
166 
 
 THE WONDERS OF SCIENCE. 
 
 diagrams, illustrative of the currents produced in 
 the atmosphere by the heating of the earth during 
 the day , and the cooling of it during the night. 
 
 “ But if the inequality of the temperature between 
 the land and the sea gives rise to such results, how 
 much greater,” mused the boy to himself, “ must be 
 the effect produced by the difference between the 
 heat of the earth at the equator — where the average 
 temperature is said to be 80° — and at the poles, 
 where it is calculated to be as low as 56° below 
 zero, the difference being as much as 136° ! 
 What a vast aerial current must be set up by such 
 means ! ” 
 
 Then the lad made another drawing, illustrative 
 of the effect that would ensue under such con- 
 
THE WONDERFUL DIFFUSION OF HEAT. 167 
 
 ditions, and he set above it a series or arrows to 
 show the direction of the currents that would be 
 thus induced in the atmosphere. For the air, being 
 heated by the vertical sun at the tropics, rises 
 there, as it does up a chimney, while the colder 
 air from the northern and southern hemispheres 
 glides in from below, on both sides of the equator, 
 to supply the place of that which has been made to 
 ascend by the heat ; precisely in the same manner 
 as, when the fire burns, fresh air is continually 
 rushing in under the door and windows. Then the 
 heated air, after rising to a considerable height 
 above the earth, at length flows over, as it were, 
 
 and forms in the atmosphere an upper current from 
 
168 
 
 THE WONDERS OF SCIENCE. 
 
 the equator to the poles, where it becomes cooled, 
 and is then drawn down to supply the place of that 
 which has been drafted from the colder to the 
 warmer regions. “ But,” said the boy, as he sur- 
 veyed the drawing, “ according to this the winds 
 which are found to prevail in the tropics should 
 blow north and south; whereas they are found to 
 come from the north-east and south-east quarters.” 
 
 Humphry puzzled himself for a long time in en- 
 deavouring to explain the phenomenon, but it was 
 more than his philosophy could accomplish ; so he 
 had to consult his old friend Mr. Tonkin again, and 
 from him he learnt that the change in the direction 
 of the currents is due to the motion of the globe and 
 the unequal rates at which different parts of the 
 earth’s surface revolve. Consequently, as the cur- 
 rents of air which set in towards the equator from 
 the poles come from parts that revolve about the 
 axis at a much slower rate than the equator itself, 
 they hang back , or drag , upon the surface, in a con- 
 trary direction to the rotation of the earth itself ; so 
 that, while the globe turns eastward, they acquire 
 somewhat of a westerly course, and, appearing to 
 come from the opposite quarter, assume, therefore, 
 the character of permanent north-easterly and 
 south-easterly winds. 
 
 But to make the matter clearer, Mr. Tonkin 
 exhibited the following illustration to the boy, in 
 which the effect of the earth’s motion in changing 
 
THE WONDERFUL DIFFUSION OF HEAT. 169 
 
 the direction of the atmospheric currents is imme 
 diately apparent. 
 
 The old gentleman, however, informed Humphry, 
 that there are other terrestrial currents produced 
 by the process of convection . In the ocean the 
 same circulation of hot and cold streams is found to 
 obtain ; for the sea, warmed by the heated shores 
 of the tropical regions, is made by convection to 
 move from the equator like a vast river, while from 
 the poles an immense current of colder liquid streams 
 forward to supply its place. For the same reason 
 as was before explained in connexion with the trade- 
 winds, the polar current having a slower rate of 
 rotatory motion assumes, on reaching the equator, 
 a westerly direction, and so flows in one broad stream 
 across the globe ; then, striking against the vast 
 continent of America, it divides into two large 
 streams. One of these flows southward down the 
 
170 
 
 THE WONDERS OF SCIENCE. 
 
 eastern coast of Southern America, and finally enters 
 the Pacific Ocean through the Straits of Magellan. 
 The other turns northward, enters the Gulf of 
 Mexico, sweeps round the coast in a powerful cur- 
 rent known as the Gulf Stream, and then proceeds 
 along the Northern American shores to the coast 
 of Newfoundland, where it crosses the world again, 
 and occasionally extends even to the western shores 
 of the British Isles. 
 
 The direction of these oceanic currents is in- 
 dicated in the subjoined chart 
 
 “ There is, however,” continued Mr. Tonkin, 
 ce another great heat-stream traversing the earth, 
 though this takes place within the crust itself, and 
 is due more to conduction than convection , as in the - 
 other cases. For philosophers tell us, that the 
 daily impressions of heat which the earth receives 
 
THE WONDERFUL DIFFUSION OF HEAT. 171 
 
 from the sun, follow each other into the interior of 
 the mass, like the waves which start from the edge 
 of a canal, and, like them, become more and more 
 faint as they flow on, one after another, till they melt 
 into the general level of the internal temperature. 
 The parts of the earth near the equator,” added the 
 old man, “ are more heated by the sun than other 
 parts, and on this account there is a perpetual in- 
 ternal conduction of heat from the equatorial to the 
 northern and southern regions. Then, as all parts 
 of the earth’s surface throw off heat into space by 
 radiation, it is plain that at the poles, where the 
 surface receives but little warmth from the sun, a 
 constant waste of caloric is produced. There is 
 thus a perpetual dispersion of heat from the polar 
 parts into surrounding space, which is supplied by 
 a perpetual internal flow of heat from the equator 
 towards the poles. The radiation from the surface 
 of the earth,” Mr. Tonkin concluded, “ has its limit 
 in the temperature of the planetary space in which 
 it moves (for we may conceive our globe to be like 
 a heated ball cooling down, in vacuo\ and this has 
 been calculated to be not more than 56° below zero, 
 — which low temperature, indeed, appears to be 
 attained in the long absence of the sun in a polar 
 winter.” 
 
 The poetic boy was lost in wonder at the mar- 
 vellous results to which his investigations had led 
 him, and his mind was filled with a sense of sub- 
 
172 
 
 THE WONDERS OF SCIENCE. 
 
 limity at the thought of the enormous heat-tides 
 that are continually flowing through the atmo- 
 sphere, the ocean, and the solid crust of the earth 
 itself. 
 
 “ I’ll work it all out myself,” he cried ; “ that I 
 will. I’ll not rest until I know all that is known 
 of Nature and her wondrous ways.” 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 173 
 
 CHAPTER VIII. 
 
 THE WONDERFUL EFFECTS OF HEAT. 
 
 The effects of heat are manifold. 
 
 In the first place, an increase of temperature 
 expands or enlarges almost all bodies, while a de- 
 crease causes them to contract or become diminished 
 in bulk. 
 
 Secondly. Heat changes the form of bodies, con- 
 verting solids into liquids, and liquids into vapours ; 
 while cold, on the other hand, condenses vapours 
 into liquids, and causes liquids again to solidify or 
 congeal. 
 
 Thirdly. Heat causes ignition; that is to say, 
 it changes dark opaque substances to a bright trans- 
 parent red, rendering them capable of giving out 
 light, when their temperatures are raised to a high 
 degree, and, when increased to the highest point, 
 causing them to become even white in the fire, and 
 then endowing them with the properties of the 
 solar beams, so that their rays have the same power 
 of traversing plates of glass, and of producing che- 
 mical changes, even as the rays of the sun itself. 
 
174 
 
 THE WONDERS OF SCIENCE. 
 
 Fourthly. Combustion , or the burning of bodies, 
 with the evolution of flame, is another effect of 
 heat. There is also a species of combustion called 
 slow (erema-causis is the chemical term for it), 
 which is unaccompanied with flame — as in the rot- 
 ting of wood and other organic tissues, the rusting 
 of metals, and even the breathing of animals and 
 ourselves. In each of these processes there is the 
 same combination of a combustible body with the 
 oxygen of the atmosphere — but at a much slower 
 rate — than in the more rapid and energetic forms 
 of combustion ; and hence but slight increase of 
 temperature (if any) is discernible, while no flames 
 or luminous gases that are perceptible to our 
 senses are evolved under such conditions. 
 
 Fifthly. Phosphorescence is likewise produced by 
 heat. During combustion and ignition, bodies be- 
 come temporarily luminous ; but in states of what 
 is called phosphorescence they are permanently so ; 
 and there are many substances — such as the compact 
 phosphate of lime, the dark-blue kind of Derby- 
 shire spar, several varieties of heavy spar, and 
 powdered quartz — which acquire the property of 
 shining constantly in the dark after having been 
 made nearly red hot. 
 
 Sixthly. Electricity is induced by heat ; for it 
 has been discovered that, if a bar of the metal called _ 
 antimony be heated at one end, while the other is 
 kept cool, an electric current ensues. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 175 
 
 Lastly. Heat promotes both vegetable and animal 
 life . For not only is intense cold destructive of 
 organic existence, but the increased warmth of the 
 summer invariably calls into being an infinite num- 
 ber of plants, flowers, insects, and the many forms 
 of organised nature that give variety and grace to 
 the earth. Moreover, heat produces in ourselves, 
 and other sentient animals, a feeling of warmth , 
 and the absence of it a sensation of cold ; by which 
 we are enabled to measure — though hardly with 
 perfect accuracy — the different changes of tem- 
 perature occurring in the substances around us, and 
 also, by the agreeable impression which we derive 
 from warmth, induced to seek that degree of heat 
 which is best fitted for the promotion of our health 
 and development of our faculties. 
 
 Humphry began by studying the laws which 
 regulate the expansion of bodies under the three 
 different forms in which they exist in nature, viz. 
 solids , liquids , and gases or vapours. To deter- 
 mine the expansion of different solids, the youth 
 procured short bars of the several substances upon 
 which he had decided to experiment. The bars 
 were alt of the same length and thickness, and were 
 accompanied with a gauge, which measured their 
 dimensions at ordinary temperatures. 
 
 The following diagram illustrates the apparatus 
 
176 
 
 THE WONDERS OF SCIENCE. 
 
 Cl 
 
 _j — t employed. The first step was to 
 test the length and breadth of 
 ^ each bar that was to be used. 
 This was performed first, by 
 placing it in the gap at the upper 
 part of the gauge, and seeing whe- 
 ther it exactly fitted between the 
 notches ; and secondly, ascertaining whether it was 
 precisely of the same diameter as the hole at the 
 bottom part of the plate. This done, the bars were 
 successively plunged into hot water, when, on ap- 
 plying them once more to the gauge, they were 
 found to be so much enlarged in all their dimen- 
 sions that it was impossible to make them pass 
 through either of the apertures. After this they 
 were severally cooled down, by immersion in a mix- 
 ture of snow and salt, to the temperature of the 
 freezing-point of water, when they were discovered 
 to have considerably contracted in bulk ; so that 
 they could be passed through both of the openings 
 with perfect ease. 
 
 It was by such means Humphry ascertained 
 that different solids possessed different degrees of 
 expansibility, and that metals are more suscep- 
 tible of change of bulk than other solid bodies. 
 Each solid, however, was found to have a rate of 
 dilatation peculiar to itself. Lead , for instance, - 
 when heated, from the freezing to the boiling-point 
 of water, was discovered by measurement to have 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 177 
 
 expanded one-350th ; iron , one-800th, and glass , 
 one- 1000th. 
 
 Platinum , however, was found to be less expan- 
 sible than iron, and copper more so. Silver , on 
 
 the other hand, was more expansible than copper, 
 while tin was more so than silver ; lead , again, 
 more than tin, and zinc even more than lead : so 
 that glass was proved to be less capable of being 
 increased in bulk by heat than the metals ; whilst, 
 among the metals themselves, platinum was ascer- 
 tained to be the least expansible, and zinc the 
 most so. 
 
 On talking over these matters with Mr. Borlase, 
 the doctor told Humphry that the expansion of metals 
 was a matter of considerable importance in many 
 arts. “ For instance,” said the gentleman, “ coopers 
 put the iron hoops upon their casks in a heated state, 
 so that they may gradually contract on cooling, and 
 firmly bind the staves together. With the same view 
 the wheelwright heats the tire of his wheel, in order 
 that it may, as it cools, press strongly upon the 
 ‘ felly,’ or circumference ; and, for the same reason, 
 the plates of large boilers are united with red-hot 
 rivets, which, during their contraction on cooling, 
 draw the sheets of metal closely and securely together. 
 
 “ In the iron bridge,” continued the doctor, 
 “ which was constructed over the Severn in Shrop- 
 shire, when I was a lad, it has been found that the 
 
 N 
 
178 
 
 THE WONDERS OF SCIENCE. 
 
 arches are nearly one inch longer in summer than 
 they are in winter ; so that, if due allowance had not 
 been made for the expansion of the metal, the stone 
 piers, on which the arches rest, must have given 
 way to the pressure, long before this. The same 
 allowance for expansion, Humphry, has to be made 
 in the clamping together of stones in the con- 
 struction of church steeples ; for the changes of 
 bulk which occur in metals at different tempera- 
 tures, though comparatively small in amount, take 
 place with irresistible force.” 
 
 The perpendicularity of the walls of the Museum 
 of Arts and Manufactures, in Paris, it may be 
 added, were restored by Molard, upon the same 
 principle. In consequence of the weight of the 
 roof, the walls were bulging outward, and, in 
 order to straighten them, iron rods were laid across 
 the interior of the building, their ends being made 
 to project through the brickwork outside. These 
 rods were then heated, and, when in an expanded 
 state, a strong iron plate was passed over each end 
 of them, and screwed firmly up against the exterior 
 of the walls. As the rods cooled, they naturally 
 contracted, and drew the walls somewhat nearer to- 
 gether. The bars were afterwards again elongated 
 by heat, and again screwed up previous to their con- 
 traction ; and so, by a repetition of the process, the 
 walls were gradually brought to a perpendicular 
 position. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 179 
 
 Humphry was delighted with the ingenious ap- 
 plications of the expansion and contraction of metals 
 by heat and cold, and Mr. Borlase, observing the 
 interest he took in the subject, proceeded to explain 
 to him how, by the same principle, the alterations 
 in the length of the pendulum of a clock were “ com- 
 pensated,” and the instrument so made to vibrate 
 seconds at all seasons. For a pendulum to beat 
 exactly sixty times a-minute, he told the boy, it 
 was necessary that it should be a fraction more 
 than 39 inches long, in the latitude of London. 
 “ If, however, the pendulum be made of metal,” he 
 said, “ it will be liable to be longer in summer and 
 shorter in winter ; so that the clock will be slow 
 in the warm weather season and fast in the cold : for 
 when the bob is let down the one- 100th part of an 
 inch the clock loses 10 seconds in 24 hours, and a 
 change of temperature equal to 30° (which is nearly 
 the difference between summer and winter, in our 
 climate), will alter the length of the pendulum rod 
 about one-5000th part, and so occasion an error in 
 the rate of going of 8 seconds a-day. 
 
 “ To counteract the expansions of the metal rod 
 of the pendulum,” continued his preceptor, “ there 
 are many ingenious contrivances. The simplest of 
 these, perhaps, is as follows : — A compound bar of 
 two differently expansive metals, such as steel and 
 brass, is formed by rivetting or soldering the two 
 metals together ; for if such a bar, with the brass 
 
180 
 
 THE WONDERS OF SCIENCE. 
 
 uppermost, be placed upon a heated plate, it will be 
 found to warp or curve downwards , in consequence 
 of the expansion of the brass being greater than that 
 of the steel. If, however, on the other hand, the com- 
 pound bar be placed on a plate cooled down by a mix- 
 ture of snow and salt, it will be found to warp or curve 
 upwards , because the brass will contract the more 
 with the cold. Now, if two such compound bars, with 
 the most expansible metal at top, be placed at the 
 upper part of a pendulum-rod, one on either side of it, 
 and firmly fixed at one end, they will, as they warp 
 upwards or downwards, tend to shorten the pendulum - 
 rod when it becomes lengthened by the heat, and to 
 lengthen it when it becomes contracted by the cold. 
 
 To make this more readily intelligible to Hum- 
 phry, the doctor exhibited to him the following en- 
 gravings : — 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 181 
 
 “ Let us now,” said Mr. Borlase, as he placed his 
 finger on the centre drawing, “ suppose the pendu- 
 lum, with the compensation-bars perfectly horizontal, 
 to be vibrating seconds at a temperature of 60°, 
 and that, some few months afterwards, the heat rises 
 to 80° ; in such a case, of course, the pendulum-rod 
 would be elongated hy the heat , and the longer the 
 rod the slower the vibrations, so that it would then 
 vibrate less than sixty times in the minute. The 
 effect of the increase of temperature, however, on 
 the compensation-bars (the most expansible metal 
 being uppermost), would be to warp them down- 
 wards , (as shown in the left-hand drawing),” said 
 the doctor, pointing to the illustration, “ and thus 
 they would shorten the pendulum-rod as much as 
 the heat had lengthened it. In cold weather, how- 
 ever, Humphry, the metal rod of the pendulum 
 would be diminished in length ; but then the com- 
 pensation-bars would warp upwards , and so tend to 
 elongate it, to the same extent as it had been con- 
 tracted by the cold (as may be seen on reference to 
 the picture on the right hand).” 
 
 The next day Humphry was busy making experi- 
 ments concerning the expansion of liquids . He 
 
 first took a large thermometer tube and poured into 
 it a sufficient quantity of spirits of wine to fill the 
 bulb at the bottom and make the fluid rise some few 
 inches in the stem above. Then, having marked 
 
182 
 
 THE WONDERS OF SCIENCE. 
 
 upon the glass with a file the level at which the spirit 
 stood at an ordinary temperature, the boy plunged the 
 instrument into a vessel of boiling water, and imme- 
 diately beheld the liquid rise in the tube till it stood 
 several inches above its former level. After this he 
 immersed the tube in a mixture of snow and salt, and 
 found the liquid contract, so that it fell in the stem 
 almost down to the bulb. On removing the instru- 
 ment, however, the fluid immediately commenced 
 rising again, and so pleased was the youth with the 
 motions that he repeated the experiment over and 
 over again, being not a little delighted to perceive 
 that each time, as he plunged the instrument into the 
 hot or cold bath, the spirit invariably rose or fell 
 to precisely the same place in the tube. 
 
 To measure the different rates of expansion among 
 different liquids, the young chemist provided himself 
 with a long and narrow glass tube, which was gra- 
 duated into cubic inches, and into this he poured a 
 certain quantity of the liquid he wished to experi- 
 ment upon. Then plunging the graduated tube into 
 the snow-and-salt mixture, he noted the precise 
 volume of the fluid at that temperature; after which 
 he immersed it in a vessel of boiling water, and then 
 noted again how many cubic inches it occupied in 
 the tube at the higher temperature; so that the dif- 
 ference told him how much the liquid had been ex- 
 panded between 32° and 212°, or the freezing and 
 boiling point of water. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 183 
 
 It was thus the lad ascertained that 9 measures 
 of spirits of wine at 32° become expanded into 10 
 measures at 212°, and 9 measures of strong aqua- 
 fortis also become 10, between the same extremes 
 of temperature. Again, 12 measures of olive oil 
 are increased into 13, while 14 of ether and the 
 same quantity of oil of turpentine swell each into 
 15, with the like increase of heat. Then 17 mea- 
 sures of oil of vitriol, at the freezing-point of water, 
 are dilated into 18 at the boiling-point, and 22 f 
 measures of water are increased to 23 f within the 
 same range of temperature, while 55 \ of quicksilver 
 become 56 J when similarly treated ; consequently 
 spirits of wine is no less than 6 times more expan- 
 sible than quicksilver, so that in the depth of winter 
 100 pints of spirits of wine are dilated into 105 in 
 the height of summer. 
 
 While making his experiments, however, as to 
 the rate of expansion in liquids, the boy had been 
 astonished to perceive, when the tube contained 
 water, that, on placing it in the mixture of snow 
 and salt, the liquid, as it was cooled down, con- 
 tinued to shrink till it had attained the temperature 
 of about 40° ; and then, instead of contracting any 
 farther (as was the case with other liquids till they 
 froz.e), it began to expand slowly , and kept rising 
 in the tube until it congealed . He noticed, too, 
 that, when the water was at its freezing point, or 
 32°, it was of the same bulk as it was at 48 ° ; so 
 
184 
 
 THE WONDERS OF SCIENCE. 
 
 that it expanded just as much for the 8° below 40° 
 as it had contracted in the 8° above that point. 
 
 Humphry then tried another experiment illus- 
 trative of this remarkable property of water. 
 Having produced two cylindrical glass vessels, he 
 surrounded one of them at the bottom with a cir- 
 cular tin tray, that fitted closely to the exterior of 
 the cylinder, and affixed to the other a similar 
 tray, but this he placed at the upper, instead of the 
 lower part of the cylinder as before — in the manner 
 represented in the subjoined engraving: — 
 
 A thermometer then having been placed in each 
 of the glass vessels, they were respectively filled 
 with water at 50°, while a freezing mixture of 
 pounded ice and salt was placed in each of the 
 trays. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 185 
 
 After the temperature of the whole of the water 
 in both vessels had been reduced to 40°, it was 
 found by the thermometer in the vessel, with the 
 freezing mixture at the top , that the cooling effect 
 would not proceed downwards, hut was limited 
 to the surface , where the water ultimately froze ; 
 for the ice-cold water being lighter than the water 
 below at 40°, necessarily floated like oil upon the 
 surface. In the other cylinder, however, where 
 the cold was applied at the lower rather than 
 the upper part of the water, the effect was very 
 different ; for there, the liquid becoming lighter, 
 as its temperature sank below 40°, ascended , whilst 
 the warmer and heavier water at the top descended , 
 until it was cooled, and so expanded in its turn ; 
 and thus the whole of the liquid was ultimately 
 reduced to the freezing-point ; whereas in the other 
 cylinder this effect was limited to the surface only. 
 Humphry now could see the reason why lakes and 
 ponds froze only on the surface, and why, on break- 
 ing the ice (as he had repeatedly done when out 
 snipe-shooting with his uncle, Leonard Millett), 
 the water underneath was always found to be 
 w r armer than the air above. 
 
 The lad had now but to investigate the rate of 
 expansion among aeriform bodies , or gases , to com- 
 plete this part of the subject. 
 
 Accordingly, he took the thermometer tube he 
 
186 
 
 THE WONDERS OF SCIENCE. 
 
 had before used, and placed it, with its open end, 
 downwards, in a glass of water, thus : — 
 
 The tube was of course filled with air, so he 
 applied his palm to the bulb, and found the heat 
 of the hand sufficient to expand the air within, and 
 drive a stream of bubbles up through the water. 
 On removing the source of heat, however, the 
 volume of air began to contract, and the liquid 
 to mount in the tube, so that he could see by the 
 height the water rose in the stem the amount of 
 expansion which the air had undergone. 
 
 Humphry then proceeded to ascertain the amount 
 of expansion produced in a given quantity of air, 
 when heated from the freezing to the boiling point 
 of water, and discovered that 100 cubic inches of 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 187 
 
 air at 32° become dilated to 1 37 J cubic inches at 
 212°. Air, therefore, at the freezing-point, ex- 
 pands one-4S0th for every degree of heat that is 
 added to it ; so that 480 cubic inches at 32° be- 
 come 481 at 33°, and 482 at 34°, and so on, the 
 volume expanding one cubic inch with each addi- 
 tional degree of heat. A volume of air, therefore, 
 at 32° would be doubled at 480°, and tripled at 
 960°, the latter temperature being that of a dull- 
 red heat. 
 
 Steam, and other vapours, when heated by them- 
 selves, are subject to the same law of expansion 
 as air. 
 
 But although the expansion produced in aeriform 
 bodies by heat is great in amount, the actual force 
 which is thus developed is small when compared 
 with that of solids and liquids under the same cir- 
 cumstances. This is owing to the extreme elas- 
 ticity of aeriform bodies ; so that, although air be- 
 comes tripled in volume at a red heat, vessels are 
 easily found capable of sustaining the pressure of 
 the expanded fluid. It is only when a portion of 
 liquid is present, so that volume after volume of 
 vapour is added to those already generated — as in 
 the production of steam — that, on resisting the ex- 
 pansion, the pressure becomes enormous, and mounts 
 up to a dangerous point. 
 
188 
 
 TIIE WONDERS OF SCIENCE. 
 
 CHAPTER IX. 
 
 THE WONDERFUL EFFECTS OF HEAT ( Continued ). 
 
 “ But heat,” said Humphry to himself, as he re- 
 viewed his previous experiments, “ not only ex- 
 pands the bulk of different bodies, but it changes 
 their form , rendering certain solids liquid, and con- 
 verting liquids into vapours. Let us see now what 
 occurs during such changes.” 
 
 Accordingly, the youth proceeded to pound some 
 ice, and to cool it down in a tumbler by means of a 
 freezing mixture to the temperature of zero. The 
 tumbler was then inserted in a bath of tepid water, 
 the temperature of which was maintained, by an 
 argand-lamp beneath it, constantly at 60°. A ther- 
 mometer having been plunged in the ice, the quick- 
 silver was observed to mount rapidly in the tube 
 until it reached 32°, when the ice began to liquefy. 
 But, though another thermometer in the water-bath 
 showed that the liquid there was still 60° hot — the 
 same temperature, indeed, as when the ice was first 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 189 
 
 immersed in it — nevertheless the thermometer in 
 the tumbler remained stationary at 32° — the 
 freezing-point. Nor did it begin to rise until the 
 whole of the ice was melted ; after which it mounted 
 gradually, and ultimately settled at 60°, the tem- 
 perature of the surrounding water. 
 
 Humphry was astonished at the effect. “ Why 
 did the thermometer,” he asked himself, “ remain 
 fixed at the freezing-point until the whole of the 
 ice was melted ? The heat from the surrounding 
 water must have been entering the ice as much 
 when it began to dissolve, as it did before the 
 thawing occurred, or even afterwards. How, then, 
 came it that the thermometer was not affected by 
 it?” 
 
 The eager boy was so puzzled with the mystery, 
 that he could not rest till he had tested the result 
 by another experiment. 
 
 Having procured two small glass globes, he filled 
 them both with the same quantity of water. The 
 liquid in one he froze, and that in the other he 
 cooled down to 33°, so that it might be as near as 
 possible to the temperature of the first, without 
 being solid. When the ice in the one globe had 
 just begun to melt, and the thermometer in that 
 vessel marked 32°, the two globes were plunged 
 into a water-bath, the temperature of which was 
 kept at 47° throughout the experiment. 
 
190 
 
 THE WONDERS OF SCIENCE. 
 
 The vessels, therefore, were, as near as possible, 
 under similar conditions of temperature, within and 
 without, and with similar contents, — except that 
 the one contained ice, and the other water. 
 
 The progress of the heating was then noted. 
 
 In the globe which contained the water , Humphry 
 found the thermometer rose in half an hour to 40°. 
 In the globe, however, which contained the ice, no 
 less than 10 J hours elapsed before the whole was 
 melted, and the temperature of the resulting liquid 
 raised to 40°, like the other ; so that the rate of 
 heating in the ice-vessel was 21 times slower than 
 in that which held the water. 
 
 “How can this be?” mused the boy -philo- 
 sopher. “ The actual amount of heat received by 
 the two must have been uniform during the whole 
 time, and yet the ice took 10 J hours to have its 
 temperature raised to 40°, while the ice-cold water 
 needed only \ an hour to acquire the same heat. 
 How extraordinary !” he inwardly exclaimed ; 
 “ what can be the cause of it ? For,” said the 
 lad, as he jotted the figures down in his note-book, 
 “ the water in the globe had its temperature raised 
 7° in half an hour, consequently that must have been 
 the rate at which the warmer liquid in the external 
 bath was giving out its heat to the two globes. 
 Accordingly, in 10 J hours it must have given 10 \ 
 times 7°, or 147° in all, to the one containing the 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 193 
 
 ice. Consequently the ice required 140 more de- 
 grees of heat to raise its temperature to 40° than 
 the water did.” 
 
 Humphry still doubted the accuracy of his 
 conclusions ; for they were so marvellous and un- 
 expected by him, that he sat for a long time con- 
 sidering by what experiment he could bring the 
 matter to a positive test. “If,” he inwardly ex- 
 claimed, “ the ice really received 140° more heat 
 than the water, what became of them ? The two 
 were each, in the end, of the same temperature ; 
 and the thermometer didn’t show, nor could I 
 feel, that the one had imbibed more heat than the 
 other.” 
 
 Presently the boy started to his feet, for a sudden 
 thought had struck him. He would take 12 oz. of 
 pounded ice, and upon this he would pour the same 
 weight of hot water, at a temperature of 172° ; so 
 that the difference between the heat of the ice and 
 that of the water would be 172° — 32°, or exactly 
 140°, and this was precisely the quantity of heat 
 that the ice in the previous experiment had received 
 over and above the water. 
 
 Humphry wondered again and again, as he pre- 
 pared the experiment, what the result would be ; 
 and when he mixed the warm water with the ice, 
 he was overjoyed to find that the temperature pro- 
 duced was only 32° — the same as that of the 
 pounded ice itself. Hence it was plain the water 
 
392 
 
 THE WONDERS OF SCIENCE. 
 
 had lost exactly 140° of its heat, and, moreover, 
 that these had entirely disappeared , since the tem- 
 perature of the colder substance remained the same 
 as at the outset of the experiment. 
 
 Then came the question, — -What had become of 
 the lost heat ? Where had it gone ? What effect 
 had it produced ? 
 
 There was but one answer ! and this Humphry 
 was not long in divining. The heat which had 
 disappeared had combined with the ice, and its 
 effect had been, not to raise its sensible temperature, 
 but simply to convert the solid body into a liquid 
 one, so that the caloric had become latent , or im- 
 perceptible to the senses, as well as incapable of 
 being detected by the most delicate thermometer. 
 
 “ So, then,” cried the boy, as the new thought 
 flashed upon him, “ a liquid is merely a solid , 
 whose particles are kept asunder by so much heat , 
 which is insensible to us. In this piece of wax the 
 particles are held together by a certain force, which 
 is called the “ attraction of cohesion,” so that when 
 I press upon it I am incapable of separating one 
 part of it from another. If, however, I apply but 
 a little heat to the substance, the cohesion is soon 
 destroyed, and the particles, instead of then firmly 
 adhering one to another, become free to move, and 
 are, consequently, easily separable ; so that a rod 
 can be plunged into it when liquefied, and moved 
 about in it with little or no difficultv.” 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 193 
 
 “ Yes,” he repeated, “ a liquid is merely a solid, 
 whose particles are kept asunder by heat.” 
 
 Humphry was so pleased with the result he had 
 arrived at, that he varied the experiment in a 
 number of different forms. 
 
 First, he took some spermaceti (a substance 
 which melts at 112°), and found that a thermometer 
 plunged in this (as in the ice) remained stationary 
 at the melting-point until the whole was liquefied, 
 and that it was not till then that the temperature 
 could be raised above the point of liquefaction. 
 
 Next he tried the same experiment with some 
 lead, and found that, though he heated a ladle-full 
 nearly red hot, the temperature of the whole was 
 immediately cooled down again to the fusing-point 
 by the addition of a piece of the solid metal. 
 
 Hence the law was manifest, that in all cases of 
 liquefaction a certain quantity of heat , not indi 
 cated by the thermometer , is absorbed , or disap- 
 pears — this heat being withdrawn from surrounding 
 bodies , and so leaving them comparatively cold. 
 
 Accordingly, now that Humphry had ascertained 
 that liquefaction itself was a source of cold, he pro- 
 ceeded to try what degree of cold he could produce 
 by causing certain substances to melt rapidly. 
 
 For this purpose he took some snow and sprinkled 
 a little salt over it, when he observed that the two 
 solids immediately formed a liquid ; and then, 
 plunging a thermometer into the mixture, he beheld 
 
 o 
 
194 
 
 THE WONDERS OF SCIENCE. 
 
 the quicksilver sink and sink, until it had nearly 
 reached zero, so that it fell from 32° to 0°. Then 
 the boy made a mixture of 5 parts of smelling salts, 
 5 parts saltpetre, and 16 parts water, and plunging 
 the thermometer into this, he found that it sank 
 from 50° (the temperature of the room in which the 
 experiment was made) to 10° (which is several de- 
 grees below freezing-point). With a mixture, con- 
 sisting of equal parts of saltpetre, ammonia, and 
 water, the thermometer fell 6° lower than in the pre- 
 vious experiment — or from 50° to 4°. Again, with 
 5 parts of Glauber’s salts and 4 parts of oil of vitriol 
 and water, the temperature sank 1° lower still — or 
 from 50° to 3°. Further, having finely powdered 
 some of the crystals of the last-mentioned salt, he 
 drenched them with muriatic acid, when the salt 
 dissolved to a greater extent than it had previously 
 done in the water, and the consequence was that 
 the temperature fell even lower than before — or 
 from 50° to 0°, while the vessel in which the mix- 
 ture was made became covered' with hoar frost; 
 and when some water in a tube was plunged into 
 the liquefied salt, it was speedily converted into a 
 mass of ice. 
 
 Humphry was now anxious to see whether the 
 heat which is absorbed, and becomes latent or in- 
 sensible during the liquefaction of bodies, really 
 remains in the liquid, and whether it is given out 
 again or emitted during their solidification. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 195 
 
 To satisfy himself upon this point he prepared 
 two vessels, one full of water and the other full of 
 brine, the temperatures of the liquids in each being, 
 at first, precisely 52°. On a very cold day, when the 
 thermometer stood at 22° (*. e. 10° below freezing- 
 point), the boy exposed the fluids in these two 
 vessels, with thermometers in each, to the open air, 
 and found that they both gradually parted with 
 their heat to the surrounding atmosphere, and were 
 soon cooled down to 32°; then the water began to 
 freeze very slowly, and during this the thermometer 
 in the water-vessel remained perfectly stationary. 
 The brine, however (which does not congeal till its 
 temperature sinks to 4°), continued to cool on, the 
 thermometer in it sinking without interruption, 
 until it gradually reached the temperature of the 
 external air, or 22°. 
 
 Now it was plain that both liquids, in cooling, 
 were alike parting with their heat to the colder air. 
 Why, then, should one and not the other suddenly 
 cease giving out caloric , and refuse for a certain 
 time to be cooled down to the same level as the 
 atmosphere around it ? 
 
 The only explanation of the problem was, that 
 the water, during the process of freezing, was part- 
 ing with the 140° of heat which Humphry had 
 before seen were necessary to retain it in a liquid 
 form, and that it was the evolution of this amount 
 of caloric which served to keep the temperature of 
 
196 
 
 THE WONDERS OF SCIENCE. 
 
 the water for a considerable time at 32° — notwith- 
 standing the cooling effect of the surrounding atmo- 
 sphere. 
 
 Still this experiment hardly satisfied the boy 
 He wanted to have some sensible proof of the evo- 
 lution of heat from water during the act of freezing. 
 It was true, there was no way of accounting for the 
 fact of the thermometer remaining stationary in one 
 vessel while it was continually sinking in the other, 
 except by supposing that the latent insensible heat 
 was being given off from the water as it passed 
 into the solid form. Humphry desired, however, to 
 see , as it were, the heat so given off, — that is to say, 
 he wished to behold the thermometer rise instead 
 of merely remaining fixed at one point . 
 
 Accordingly it struck the lad, that if he was to 
 keep some water in a vessel perfectly still, and to 
 prevent even the air from agitating its surface, he 
 might be able to cool it down some few degrees 
 below the freezing-point, and then he should be 
 able to see if, in the act of freezing afterwards, the 
 thermometer would really rise as the water solidi- 
 fied. So successfully did Humphry perform this ex- 
 periment, that he was enabled, by great care, to 
 cool some water in a vessel down to 22° without 
 freezing it. Then he felt a thrill dart through his 
 frame as he agitated the water, and beheld it im- 
 mediately shoot into a thousand transparent crys- 
 tals, — whereupon the thermometer in the vessel 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 107 
 
 instantly began to rise, and soon stood at 32°, 
 thus showing that the water had acquired 10° of 
 heat almost in an instant. 
 
 Whence came this heat, then ? 
 
 But one answer was possible. It was manifest 
 that the water, in the act of solidifying, gave 
 out heat, even as in the act of liquefying ice 
 absorbed it. 
 
 “ But do all things,” said Humphry to himself, 
 “ give off heat as they pass from a liquid to a 
 solid form ? And is solidification, therefore, a 
 heating process to surrounding bodies, in the same 
 manner as liquefaction (from the absorption of heat 
 at such times) is a cooling one ? ” 
 
 The youth had heard that, if a strong solution of 
 Glauber’s salts be poured, while hot, into a flask, 
 and corked tightly down, it will remain liquid when 
 cold, and that on removing the cork it will imme- 
 diately shoot into a fibrous mass of crystals. He 
 wished to see, therefore, whether, in the act of solidi- 
 fication, heat is evolved from such a solution. 
 
 Humphry was not long in preparing the requi- 
 sites for the experiment, and was then delighted to 
 find, as he watched the crystals, immediately that 
 he withdrew the cork, dart from the surface down- 
 wards, the temperature of the substance became so 
 much increased, that the bottle which contained it 
 grew sensibly warm in his hand, though it was 
 perfectly cold before. 
 
198 
 
 THE WONDERS OF SCIENCE. 
 
 Now the lad knew, that in making the solution 
 he had added 2 ounces of water to 3 ounces of 
 the salts, and as the whole of this became solidified 
 on opening the bottle, it was clear that the eleva- 
 tion of temperature arose principally from the 
 solidification of the water in the crystalline mass. 
 
 Next Humphry added a saturated solution of 
 tartaric acid to some strong liquid ammonia, and 
 found, immediately that the two fluids were poured 
 together, a solid substance was thrown down, and 
 considerable heat evolved. 
 
 Again, the lad was aware that, on mixing pow- 
 dered plaster of Paris with water, there is a like 
 increase of temperature at the moment of the com- 
 position “ setting or, in other words, when the 
 water with which the plaster has been mixed 
 passes into the solid form. 
 
 Further, he could now perceive that the great in- 
 crease of heat which occurs during the slacking of 
 lime is due merely to the same cause, viz. the solidi- 
 fication of the water poured upon it. Consequently 
 it was plain that water, in passing from the liquid 
 to the solid form, invariably evolves the heat which 
 is necessary to retain it in a liquid state, and 
 which as it passes, on the other hand, from the 
 solid to the liquid state, it as invariably absorbs. 
 
 Not only, however, is there an increase of tern- - 
 perature when water becomes solid, but Humphry 
 found the same result to ensue, even when the same 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 199 
 
 liquid is condensed . On mixing 4 parts of strong 
 oil of vitriol with 1 part of water, cooled down to 
 the freezing-point, he perceived that the two to- 
 gether occupied considerably less space than they 
 did alone, and that the mixture rose rapidly from 
 32° to 212°, or from the freezing to the boiling point. 
 The same result ensued when 1 part of snow was 
 substituted for the 1 part cold water ; but, strange to 
 say, when the proportions were reversed, so that 
 there were 4 parts of snow to 1 part of oil of vitriol, 
 intense cold instead of intense heat was produced, — 
 the increase of temperature in the one case arising 
 from the condensation of the water from the snow, 
 and the decrease of temperature, on the other hand, 
 being due to the liquefaction of the snow itself. 
 
 Moreover, the boy was aware that a piece of soft 
 iron, when hammered, becomes intensely heated ; 
 and he had heard that when a bar of red-hot iron 
 is passed through a rolling-mill, its temperature is 
 so much raised that it is rendered nearly white 
 hot by the extreme pressure, and the consequent 
 condensation of the particles. 
 
 Sudden expansion , on the other hand, Humphry 
 found to be a cooling process ; and this is one of 
 the reasons why high-pressure steam, on issuing from 
 a small aperture, instead of scalding the hand as 
 ordinary steam would, scarcely feels warm, even 
 though its temperature be some hundred degrees 
 higher than the vapour at a low pressure ; for as 
 
200 
 
 THE WONDERS OF SCIENCE. 
 
 the compressed steam escapes into the atmosphere, 
 its instantaneous expansion so far cools it, that it 
 is deprived of all power of burning. 
 
 Moreover, at the fountain of Hiero, in Hun- 
 gary, a part of the machinery for working the 
 mines consists of a column of water 260 feet 
 high, which presses upon a large volume of air, 
 enclosed in a tight reservoir, so that the air 
 within is greatly condensed by the enormous 
 weight of the water ; and that when a pipe com- 
 municating with this reservoir is suddenly opened, 
 the condensed air rushes out with extreme velocity, 
 and then instantly expanding, absorbs so much heat 
 as to precipitate the moisture it contains in a 
 shower of snow — a hat held in the blast being 
 immediately covered with it. So strong, however, 
 is the current of condensed air, that the workman 
 who holds the hat is obliged to lean his back 
 against the wall to retain it in its position. 
 
 Another illustration of the cooling effect pro- 
 duced by the sudden expansion of condensed air 
 is afforded in the fact, that if the blast from an 
 air-gun be directed upon a delicate thermometer, 
 the temperature will be found to be lowered at 
 the moment of the discharge. 
 
 As yet Humphry had dealt only with the effects 
 produced by the conversion of solids into liquids, 
 or liquids into solids, and there still remained for 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 201 
 
 him to learn what results ensued when liquids were 
 changed into vapours , or vapours into liquids . 
 
 Accordingly he proceeded to heat some water in 
 an open vessel, and found, as the temperature 
 gradually rose, that the vapour continued to form 
 on its surface till the thermometer reached 212°, 
 when the liquid became violently agitated. But 
 then, although the fire was kept up beneath the 
 vessel as strong as at first, and the heat continued 
 to flow into it as before , the quicksilver in the 
 thermometer became stationary, and remained so 
 until the whole of the liquid had been dissipated 
 in the form of steam. 
 
 Here, then, was another instance of the absorp- 
 tion of heat during a change of form ; and it was 
 evident, that as water required a certain amount 
 of temperature in order to convert it from a solid 
 into a liquid state, so did it need a proportionate 
 supply of heat to change it from a liquid into 
 a vapour. 
 
 “ The heat absorbed during the boiling passed 
 olfi, perhaps, in the steam,” thought Humphry. 
 
 On testing the temperature of the vapour, how- 
 ever, it was found to be no hotter than that of 
 the water during its ebullition. 
 
 What, then, had become of the heat which had 
 been added since the boiling commenced ? 
 
 Why, it had been rendered latent or insensible , 
 being necessary for retaining the liquid in a more 
 
202 
 
 THE WONDERS OF SCIENCE. 
 
 rarified form; for as a liquid is but a solid whose 
 particles have been separated, and so made free to 
 move, by the latent heat existing between them, so 
 a vapour is merely a liquid, whose atoms have been 
 driven farther asunder, and made still more easily 
 separable, by the heat imbibed during the process 
 of vaporization. It was evident, therefore, that 
 the production of vapour is attended with a loss of 
 sensible heat, and that, as in the case of liquefac- 
 tion, heat disappears in order to constitute the 
 liquid, so in the case of evaporation a considerable 
 quantity of heat becomes latent in the vapour. 
 
 To render this part of the subject still more 
 clear, Humphry filled a flat-bottomed tin vessel 
 with a definite quantity of water, at the tempera- 
 ture of 50°. Then, having placed the vessel upon 
 a heated plate, he found that in 4 minutes it had 
 acquired a temperature of 212°, and began to boil, 
 whilst in 20 minutes the whole had evaporated, 
 having been dissipated in the form of steam. The 
 water, therefore, had received 212° — 50°, or 162° of 
 heat in 4 minutes, which is at the rate of 40|° in each 
 minute. The heat, however, continued to flow into 
 the water at the same rate during the whole 20 
 minutes, so that the entire amount of heat received 
 must have been 40|° x 20°, or 810°, and this had 
 become latent in the steam. Consequently the total 
 quantity of heat required to evaporate boiling water 
 would be sufficient to raise the water — provided 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 203 
 
 it remained all the time in the liquid state, instead 
 of being converted into steam — as much as 810° 
 above the boiling-point, or altogether to 1022°. 
 
 To verify this conclusion, Humphry heated some 
 water under pressure in a “ Papin’s digester,” so that 
 the liquid was prevented evaporating, and raised 
 the temperature of it to 400°. Then the lad 
 opened the valve, and part of the water suddenly 
 rushed out in the form of steam, when the tem- 
 perature of that remaining in the digester sank im- 
 mediately to 212°. Consequently 188° (400° —2 12°) 
 of heat had suddenly disappeared, having been car- 
 ried off by the steam. It was afterwards found that 
 only -|-th of the water had gone off in vapour, so that 
 this vapour must have contained not only its own 
 188°, but the 188° lost by the 4 other parts re- 
 maining in the digester ; that is to say, the steam 
 must have contained 188° x 5°, or 940° of heat 
 altogether. This experiment therefore showed, that 
 steam is water combined with nearly 1000° of 
 heat ; and in the same manner as the water had 
 been previously observed to give out its heat of 
 liquidity, and to make the thermometer rise at 
 the moment of its conversion into ice , so was it 
 now seen to absorb a considerable amount of heat, 
 and to make the thermometer fall at the moment 
 of its conversion into vapour . 
 
 Evaporation, therefore, should be a means of pro- 
 ducing cold, in the same manner as liquefaction had 
 
204 
 
 THE WONDERS OF SCIENCE. 
 
 been previously proved to be ; for if it be necessary, 
 in order to convert liquids into vapours, that a cer- 
 tain amount of heat be absorbed, it is plain that 
 such heat must be drawn from surrounding sub- 
 stances, and thus the vaporization of one body will 
 be a cooling process to others near it. 
 
 To test this, Humphry spread out a wet cloth in 
 a keen wind when the atmosphere was a few de- 
 grees above the freezing point, and found that the 
 particles of water, as they passed into the form of 
 vapour,* carried off so much heat fiom the liquid in 
 the cloth (in the same manner as the steam did in 
 the Papin’s digester) that the remainder became 
 frozen, while the cloth itself was rendered hard 
 and stiff by the formation of ice in its pores. 
 
 Humphry, however, knew that ether was much 
 more vaporisable than water at ordinary tempera- 
 tures. Accordingly he availed himself of this sub- 
 stance in the production of cold by spontaneous 
 evaporation. 
 
 First, he folded a strip of cambric round the 
 bulb of a small thermometer, and allowed some 
 ether to dribble over it, while he increased the 
 evaporation by projecting a current of air upon it 
 by means of a bellows. The quicksilver was im- 
 mediately seen to fall several degrees below the 
 freezing - point, and on substituting a thin glass 
 
 * Evaporation goes on more or less rapidly at all temperatures. 
 
J 
 
 THE WONDERFUL EFFECTS OF HEAT. 20 ? 
 
 tube containing a small quantity of water for the 
 thermometer previously used, the boy was enabled 
 to produce ice by the same means. 
 
 Next, the lad made use of the air-pump which he 
 had previously constructed out of the rudest ma- 
 terials,* in order to facilitate the spontaneous eva- 
 poration of water, by removing the pressure of the 
 atmosphere from the surface of it. 
 
 Upon the plate of the apparatus he placed a soup- 
 plate, and this he half tilled with oil of vitriol ; above 
 the soup-plate he stood a tin basin, supported on three 
 pieces of tobacco-pipe, and three parts filled with 
 
 * Dr. Paris, in his “ Life of Davy” (p. 37), relates the following 
 anecdote concerning the construction of this apparatus: — “A 
 French vessel having been wrecked off the Land’s End, the sur- 
 geon escaped, and found his way to Penzance. Accident brought 
 him acquainted with Humphry Davy, who showed him many 
 civilities, and in return received, as a present from the surgeon, a 
 case of instruments which had been saved from the ship. The 
 contents were eagerly turned out and examined by the young 
 chemist ; not, however, with any professional view as to their 
 utility, but in order to ascertain how far they might be con- 
 vertible to experimental purposes. The old-fashioned and clumsy 
 glyster apparatus was viewed with exultation, and seized in 
 triumph. What reverses may not be suddenly effected by a 
 simple accident! So says the moralist. Reader, behold an 
 illustration : in the brief space of an hour did this long- neglected 
 and unobtrusive machine, emerging from its obscurity and insig- 
 nificance, figure away in all the pomp of a complicated piece or 
 pneumatic apparatus. Nor did its fortunes end here ; it was 
 destined for greater things ; and we shall hereafter learn that 
 it actually performed the duties of an air-pump in an original 
 experiment on the nature and sources of heat.” It is but right to 
 add, that Dr. Davy doubts the truth of the above story. 
 
THE WONDERS OE SCIENCE. 
 
 a 06 
 
 water, in which a small thermometer was immersed ; 
 while over the whole he put the glass receiver. 
 The arrangement is shown in the annexed illus- 
 tration : — 
 
 The pump was now set to work, and the air 
 gradually drawn out from the glass receiver, where- 
 upon the thermometer was observed to sink ; for as 
 the pressure of the atmosphere was removed the 
 evaporation from the water was increased, while 
 the oil of vitriol at the bottom served to absorb the 
 vapour as fast as it was produced : so that, though 
 the temperature was considerably lowered, the eva- 
 poration from the water ultimately became so rapid 
 that it had all the appearance of boiling, and in the 
 course of 5 or 10 minutes the liquid was converted 
 into ice. 
 
 Before the solidification took place, however, the 
 thermometer was observed to fall several degrees 
 below the freezing point, whilst at the moment of 
 
THE WONDEKFUL EFFECTS OF HEAT. 
 
 207 
 
 its freezing it rose to 32°, in consequence of the 
 escape of the heat which had previously served to 
 keep the water liquid. 
 
 The explanation of the process is almost obvious. 
 As in the case of the steam issuing from the Papin’s 
 digester, that part of the water passing off in the 
 form of vapour abstracted heat from the remainder 
 of the fluid portion, which, thus losing the caloric 
 that served to keep it liquid, became solid, or froze. 
 
 Humphry was now anxious to see what effect the 
 simultaneous evaporation of ether and water would 
 produce under the air-pump. Accordingly he pro- 
 cured a thin glass flask, and this he inserted in a 
 tumbler, so that it fitted almost close. Having 
 poured a little ether into the flask, and some cold 
 water into the tumbler, he placed the whole appa- 
 ratus under the receiver of the air-pump, as here 
 represented : — 
 
 On exhausting the receiver the ether was ob 
 
208 
 
 THE WONDERS OF SCIENCE. 
 
 served to boil , from the rapidity of its evaporation, 
 while the water in which it was immersed soon be- 
 came solidified, or converted into ice. 
 
 The apparent anomaly of two liquids made to 
 boil and freeze at one and the same time puzzled 
 the lad for a while. At length, however, he di- 
 vined the reason. The ether, in passing into the 
 form of vapour, required a certain amount of heat 
 to sustain it in that state, and this it absorbed prin- 
 cipally from the water that surrounded it, which 
 soon became congealed owing to the loss of that 
 portion of heat which was requisite for its main- 
 tenance in a fluid form. 
 
 Humphry had now discovered that, by removing 
 the pressure of the atmosphere, the evaporation of 
 liquids proceeded at a much greater rate, and he 
 was anxious to learn whether they could be made 
 to boil at a lower temperature by the same means. 
 
 Accordingly, he fitted a stop-cock into the neck 
 of a Florence flask, and then turning the cock on, 
 so that the vapour might escape, he proceed to heat 
 the water, over the flame of a spirit-lamp, till it boiled ; 
 whereupon he removed the flask from the flame and 
 closed the cock. The liquid then soon ceased to boil ; 
 on plunging the flask, however, into a vessel of cold 
 water, he found the ebullition instantly to recom- 
 mence, but to cease again directly the vessel was 
 held near the fire or over the lamp. Now during the 
 boiling, in the first instance, all the air above the 
 
/ 
 
 THE WONDERFUL EFFECTS OF HEAT. 209 
 
 liquid had been driven out of the flask, and re- 
 placed by an atmosphere of steam ; this, upon 
 plunging the vessel into cold water, had become 
 condensed into a liquid form, so that a vacuum 
 being formed above the water, the fluid boiled at a 
 lower temperature under the diminished pressure. 
 On removing the flask, however, from the cold 
 medium, a new atmosphere of steam was generated, 
 and the pressure of this on the surface of the 
 liquid prevented its boiling any longer ; and thus 
 the water was made to boil by being cooled , and 
 to cease boiling by being heated . 
 
 Humphry afterwards ascertained, that if a glass 
 of water of the temperature of 90° or 100° be 
 placed under the receiver of an air-pump, and the 
 pressure of the atmosphere removed by exhausting 
 the air, the water boils violently at that tempera- 
 ture, and continues to do so until the whole re- 
 ceiver becomes filled with the vapour; which then, 
 pressing upon the surface of the liquid, again pre- 
 vents its ebullition. By continuing to pump out 
 the vapour, however, the boy was enabled to keep 
 the water boiling at no less than 112° below its 
 boiling-point in the open air. 
 
 With alcohol and ether, however, it was not even 
 necessary to warm them, for these fluids boil under 
 the air-pump at all ordinary temperatures. 
 
 It has likewise been found that water boils at 
 
 p 
 
210 
 
 THE WONDERS OF SCIENCE. 
 
 less than 212° upon the summit’s of hills and moun 
 tains, where the pressure of the atmosphere is con- 
 siderably diminished. At the top of Mont Blanc 
 water has been made to boil at 187°, and even when 
 the air is lighter at the surface of the earth the 
 boiling-point of all liquids is reduced ; so that in 
 this country, where the density of the atmosphere 
 fluctuates considerably, water boils sometimes at 2° 
 lower than 212°, whilst on heavy days it requires 
 to be raised to 214° in order to produce ebullition. 
 Even the cleanliness of the vessels in which the 
 liquid is heated has been ascertained to alter the 
 boiling-point. In glass vessels, from which all 
 chemical and mechanical impurities have been re- 
 moved by perfect cleaning, water may haye its 
 temperature raised as high as 220° without being 
 made to boil ; whereas a few metallic filings, or 
 other finely-divided or insoluble materials, have the 
 effect of causing it to boil at a lower temperature 
 than 212°. 
 
 Humphry would now have sought to learn how 
 much water becomes expanded in passing into the 
 form of steam. But, though he made several rude 
 experiments on the subject, he was unable, from the 
 want of proper apparatus, to arrive at any definite 
 result, and so was obliged to rest contented with 
 the knowledge which his books afforded him ; viz. - 
 that a cubic inch of water becomes converted, at 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 211 
 
 212°, into very nearly a cubic foot of steam, the 
 expansion being about 1700 times the bulk of the 
 original fluid. 
 
 Spirits of wine, on the other hand, expand only 
 493 times, ether about 212 times, and oil of tur- 
 pentine 192 times ; each at the temperature of 
 212°. Steam, however, is lighter than air, — 
 whereas the vapours of spirits of wine, ether, and 
 turpentine, are much heavier than it, the last being 
 nearly 5 times the density of our atmosphere at the 
 same temperature. 
 
 Before quitting this part of the subject, there is 
 one striking anomaly connected with the produc- 
 tion of vapour that deserves mention here, though 
 it is but a recent discovery. 
 
 If a silver, or other metal spoon, be heated to 
 redness in the flame of a lamp, and some water be 
 dropped into it while red hot, it will be found that 
 the liquid, instead of passing off at once into steam, 
 will instantly assume a globular, or spheroidal 
 form, and float about the heated metal, revolving 
 with rapidity, and evaporating very slowly ; while 
 the temperature of the liquid will remain constantly 
 helow the boiling point — so long as the red heat is 
 maintained. If, however, the lamp be withdrawn, 
 the water, as the spoon cools down, will suddenly 
 be made to boil with violence, and be dissipated 
 in vapour with almost explosive energy. 
 
 The cause of this singular phenomenon is, that 
 
212 
 
 THE WONDERS OF SCIENCE. 
 
 the water is separated from the red-hot metal by 
 an atmosphere of highly-elastic steam, which is 
 generated immediately the liquid is projected on 
 the heated surface, and which, encircling the water, 
 serves to keep it in a spheroidal, or globular state ; 
 whilst the vapour, being a bad conductor of heat, 
 prevents the temperature of the hot metal being 
 communicated to the fluid in connexion with it. 
 
 This is the reason why water, when accidentally 
 dropped upon the heated bars, or hobs of a grate, 
 is occasionally observed to run along them like 
 globules of quicksilver. If these, however, be 
 smartly struck with a hammer, so as to bring them 
 suddenly into contact with the hot metal, the glo- 
 bules will be instantaneously converted into steam, 
 and the change of form attended with a slight 
 explosion. 
 
 Another form of the same singular phenomenon 
 consists in plunging a mass of white-hot metal into 
 a vessel of cold water, when the incandescence 
 will be found to continue, rather than to be 
 quenched, in the liquid, the metal still shining 
 with a bright white light, while the water may be 
 seen to circulate around, though at some distance 
 from, the glowing mass, being separated from it by 
 an atmosphere of non-conducting vapour, which, 
 for a time, prevents its heat being communicated - 
 to, and so reduced by, the surrounding fluid. At 
 length, as the metal cools, the water around it is 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 213 
 
 brought into contact with the heated surface, when 
 it is made suddenly to boil with energy. 
 
 Moreover, if an iron shell containing water be 
 made red hot, and a hole then drilled in it, no 
 water will be found to flow through the orifice 
 until the iron has been considerably cooled, when 
 it will suddenly issue forth with great violence, in 
 the form of steam. 
 
 So, again, if water be poured upon an iron sieve, 
 the wires of which have been heated to redness, 
 it will not pass through the interstices. As the 
 sieve cools down, however, it will be found to run 
 through rapidly. 
 
 Further, if a red-hot cinder be let fall into a 
 pan of water, it will be seen to swim upon the 
 surface, and then to sink with a hissing sound, 
 accompanied with a sudden irruption of steam. 
 
 But a far more striking illustration of this strange 
 property consists in heating to redness a silver or 
 platinum capsule (or small crucible), and filling it 
 while red hot with a freezing mixture, when the 
 whole mass will instantly be thrown into the 
 spheroidal state, and on introducing a thermometer 
 therein the temperature of the liquid will be found 
 to be scarcely increased, so that a small tube filled 
 with water soon becomes frozen when immersed in 
 it ; and thus ice may thus he produced even in a 
 vessel , the heat of which is no less than 1000°. In- 
 deed, by introducing some ether and solid carbonic 
 
214 
 
 THE WONDERS OF SCIENCE. 
 
 acid into an incandescent crucible, even quicksilver 
 itself has been made to freeze in it, though this 
 requires a temperature of 82° below the freezing- 
 point of water ; and yet this extreme cold (equal 
 to that of a Polar winter) has been produced, and 
 mercury frozen inside a red-hot vessel. 
 
 Humphry, however, was anxious not to conclude 
 his investigations concerning the changes of form 
 produced by heat without ascertaining whether all 
 bodies, in passing from a lower to a higher tem- 
 perature — or, on the other hand, from a higher to a 
 lower one — absorbed the same quantities of caloric ; 
 that is to say, did one body require a greater 
 amount of heat to raise it to a given temperature 
 than another, and did some bodies give off more 
 heat than others in cooling ? 
 
 First, the lad dealt with equal quantities of the 
 same fluid at different temperatures, in order to 
 determine whether, on mixing the two together, 
 the resulting temperature amounted to the mean of 
 both. He added J pint of cold water at 50° to 
 \ pint of warm water at 100°, and found that the 
 two together gave a mean temperature of 75° 
 
 j . so that the hot water had lost 25°, whilst 
 
 the cold had gained precisely the same amount. 
 
 Then Humphry proceeded to try whether the 
 result was the same with equal quantities of dif- 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 215 
 
 f event fluids. Accordingly, he took the same 
 amount of water at 50° as he had previously em- 
 ployed for one portion, but, instead of the water 
 at 100° for the other, he substituted a like quantity 
 of quicksilver at the same temperature, and found 
 to his astonishment, on pouring the one to the 
 other, that the heat of both together was no longer 
 the mean of the two (or 7 5° as before), but only 
 66|°. In this case, therefore, the quicksilver had 
 lost as much as 33£° (100 — 66§), whilst the water 
 had gained only 16|° (66J — 50); so that the quick- 
 silver had parted ivith twice as much heat as the 
 water had absorbed. Consequently it was evident 
 that, in order to raise a certain measure of water to 
 a given temperature, it required just double the 
 quantity of heat to be added to it that an equal 
 measure of quicksilver did ; or, in other words, 
 the capacity of water for heat was twice that of 
 quicksilver. 
 
 This referred, however, only to equal measures 
 of the two fluids ; so Humphry wished to ascertain 
 whether the effect would be the same with equal 
 weights of them. He mixed, therefore, 1 pound of 
 water at 50° with 1 pound of quicksilver at 100°, 
 and discovered that the resulting temperature was 
 not quite 52°. Here, then, the quicksilver had 
 lost rather more than 48° of heat, while this amount 
 had served to increase the warmth of the water 
 only about 2°. There was but one conclusion to 
 
216 
 
 THE WONDERS OF SCIENCE. 
 
 be arrived at, therefore ; namely, that the capacity 
 of a given weight of water for heat is about 30 
 times greater than an equal weight of quicksilver 
 whereas the capacity of a given measure of the 
 former is only twice that of an equal measure of 
 the latter. 
 
 After this the boy added 1 pound of water at 
 50° to an equal weight of spermaceti oil at 100°, 
 when the temperature of the mixture was found to 
 be 66|°; so that the oil had parted with twice as 
 much heat as the water had gained. 
 
 Thus it was evident that different substances 
 required different quantities of heat to raise them 
 to the same temperature ; and that in order to 
 warm a certain weight of water to the same degree 
 as an equal weight of oil and quicksilver, twice 
 as much heat must be given to the water as 
 to the oil, and 30 times as much to the quick- 
 silver. 
 
 Still the cautious boy was anxious to test the 
 truth of this result by another experiment. 
 
 Accordingly, he took 1 pound weight of each of 
 the three substances above-mentioned, and having 
 brought them severally to a temperature of 50°, he 
 placed the flasks in which they were respectively 
 contained in a large bath of warm water, the heat 
 of which he kept constantly at 100°. This done, 
 he proceeded to note the time and manner in which 
 each of the fluids was heated, and found that when 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 217 
 
 the thermometer in the quicksilver nad reached 
 80°, that in the oil stood at 52°, while the one in 
 the flask of water marked only 51° ; and, though 
 the three liquids ultimately attained the same tem- 
 perature as the water-bath in which they were 
 immersed, the water took 30 times longer to acquire 
 that heat than the quicksilver , and twice as long as 
 the oil . 
 
 Now it was manifest that each of the liquids in 
 this experiment must have been receiving heat 
 alike, so that the only feasible explanation was that 
 the water, in order to have its temperature raised 
 to a given degree, required 30 times the quantity 
 of heat that the metallic fluid did, and double the 
 quantity of the oleaginous one. 
 
 Nevertheless, to avoid all possible chance of 
 error, Humphry repeated the experiment in another 
 form, so as to see whether, in cooling, the water 
 would part with more caloric than either the oil 
 or the quicksilver ; and just as much more, too, as 
 it had been found to imbibe while being heated. 
 
 With this view Humphry filled three Florence 
 flasks, — one with a pound of water, another with a 
 pound of oil, and the third with an equal weight of 
 quicksilver, — all at the temperature of 212°, and 
 having placed each of the flasks in a large funnel, 
 that rested on a graduated glass jar, he surrounded 
 them one after another with pounded ice, as here 
 shown : — 
 

 218 THE WONDERS OF SCIENCE. 
 
 Water . Oil. Quicksilver. 
 
 When the fluids had been severally cooled down 
 to the same temperature as the ice around them, 
 the lad proceeded to ascertain, by the quantity of 
 water produced by the thawing of the ice surround- 
 ing each flask, how much heat had been given out by 
 the three liquids respectively, in sinking from 212° 
 to 32° ; and he ultimately found that the hot water, 
 in cooling, had thawed twice as much ice as the 
 hot oil, and 30 times as much as the equally hot 
 quicksilver. Hence it was beyond doubt that 
 water, at a given temperature, contained con- 
 siderably more heat than either of the other fluids , 
 and hence the reason why it took a longer time- 
 than they to be warmed or cooled to the same 
 extent. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 / 
 
 These experiments naturally led the boy to 
 think how great a magazine of heat the sea must 
 be, and what a beneficial influence its slow rate of 
 heating and cooling must have in equalizing the 
 temperature of the atmosphere. Quicksilver, on 
 the other hand, however, having a small capacity 
 for heat, and, consequently, being quickly warmed 
 and cooled, becomes of great value as a liquid for 
 the thermometer, since it is this property that gives 
 great sensibility to the instrument. 
 
 It now only remained for Humphry to ascertain 
 the relative capacities for heat among solids. This 
 he did by cooling down equal weights of the metals 
 and other bodies under the exhausted receiver of 
 his air-pump, and noting how long they took to 
 pass each from a like higher to a like lower tem- 
 perature. 
 
 By such means the youth ascertained that Lead 
 had the smallest capacity for heat among the 
 metals, cooling more rapidly than even quicksilver 
 itself, and 34J times quicker than water. Next in 
 order came Platinum , which again had less capacity 
 than quicksilver, and cooled 32 1 times quicker than 
 water. After this, Silver was found to cool 18 times 
 quicker than water ; Zinc, lOf times : Copper , 
 10g times ; and, lastly, Iron , which was ascer- 
 tained to part with its heat only 9 times quicker 
 than water. Glass, however, was found to occupy 
 a longer time in cooling than any of the metals, 
 
220 
 
 THE WONDERS OF SCIENCE. 
 
 giving off its caloric but 8J times quicker than 
 water ; while sulphur, on the other hand, retained 
 its warmth longer even than glass, but still cooled 
 5-t times quicker than water. 
 
 Tlie capacities for heat, therefore, among the 
 above-mentioned substances, were inversely as their 
 rates of cooling : that is to say, lead, which cooled 
 the quickest, contained the least quantity of heat, 
 and, therefore, required less caloric to raise it to a 
 given temperature ; while sulphur, on the other 
 hand, which took nearly 7 times as long to cool as 
 lead, contained 7 times more heat, and required to 
 be warmed for just so much longer a period. 
 
 The relative capacity for heat among substances 
 is generally termed their “ specific heat;” for 
 as different bodies are found to possess unequal 
 quantities of heat at equal temperatures , and as 
 this exists in them in a latent or insensible state, 
 the term specific heat has therefore been adopted 
 to express the relative amount of latent caloric 
 existing in different substances at the same tem- 
 peratures. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 221 
 
 CHAPTER X. 
 
 THE WONDERFUL EFFECTS OF HEAT ( concluded ). 
 
 The young philosopher had now investigated the 
 effects produced by an elevation of temperature, not 
 only upon the bulk , but upon the form of different 
 bodies. He had found, first, that heat increased 
 the size of certain substances, without destroying 
 the cohesion among their constituent particles ; 
 and, secondly, that it loosened the attraction be- 
 tween the atoms of other substances, and ren- 
 dered them free to move: so that solids became 
 converted by it into liquids, and liquids into va- 
 pours, while the heat which was absorbed and 
 disappeared during the production of such changes 
 he had ascertained not only to exist between the 
 molecules of the resulting liquid or vapour in a 
 latent or insensible state, but to be again evolved in 
 a sensible form when the vapours became condensed 
 or the liquids solidified. 
 
 The next step, therefore, was to study the cir- 
 cumstances regulating the ignition and combustion 
 of bodies. 
 
222 THE WONDERS OF SCIENCE. 
 
 That there is an intimate connexion between the 
 principles of light and heat, Humphry had little 
 doubt. Indeed, it was plain to him that the two 
 are mutually disposed to produce each other. He 
 had, however, as yet considered only the laws of 
 heat, divested of luminosity ; but, at present, he 
 was about to examine the one in connexion with 
 the other; the laws of ignition and combustion 
 being those of the production of artificial heat, 
 accompanied with light for the time being. 
 
 Whether substances, when merely warm , are 
 capable of emitting rays of light, it is impossible 
 to determine; “ but,” said the lad to himself, “ the 
 slightest increase of temperature is perhaps accom- 
 panied with some kind of luminous power that our 
 sense of vision is incapable of perceiving, since it is 
 only when the temperature of bodies is raised to a 
 high point that they acquire the property of be- 
 coming luminous to our eyes.” 
 
 It is extremely difficult to ascertain the precise 
 temperature at which bodies, when heated, acquire 
 the property of giving out light ; for the result is 
 greatly modified, not only by the sensitiveness of 
 the eye of the observer, but also by the clearness 
 of the atmosphere at the time of making the ex- 
 periment. 
 
 The amount of heat necessary for producing- 
 luminosity, however, certainly exceeds 650°, since 
 this is the temperature at which quicksilver boils ; 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 223 
 
 and though Humphry heated the metallic fluid to 
 ebullition in a dark room, it did not become, so far 
 as he could detect, in the least degree luminous. 
 
 Subsequent experiments, however, induced him 
 to place the degree at which heated bodies begin to 
 emit light in the dark at 810° ; though the investi- 
 gations which have since been made in connexion 
 with the subject lead to the conclusion that the first 
 gleam of light which is given out from a heated 
 platinum wire occurs at a temperature of about 
 865°. The luminous rays emitted at this heat, 
 however, are not red, but of a lavender-grey colour 
 (similar to those which exist in the solar spectrum 
 beyond the violet band), and seem to be the first 
 transition from darkness to ordinary light. 
 
 At the temperature of about 1000° the light 
 emitted by the heated body becomes visible in day- 
 light , and is then of a dull-red hue. 
 
 At 1200° the tint of incandescence brightens into 
 a vivid crimson, or “ cherry-red,” as it is termed. 
 
 Then, as the temperature increases, the light 
 emitted by the glowing body assumes partly a 
 yellow colour ; so that at 1 700° an “ orange heat,” 
 as it is called, is produced. 
 
 At length, however, when the heat rises to the 
 highest point, the light emitted acquires such bril- 
 liancy as to be painful to the eye ; the incandescent 
 substances then appearing no longer tinted, but 
 positively colourless in the fire. This constitutes 
 
224 
 
 THE WONDERS OF SCIENCE. 
 
 what is denominated a “ white heat,” and occurs 
 at no less a temperature than 3000°.* 
 
 At this intense temperature a remarkable change 
 is found to occur in the character of the heat itself, 
 for it has been before shown that the heat-rays 
 emanating from an ordinary fire are stopped by 
 glass ; so that while the light emitted by the burn- 
 ing coals passes freely through plates of glass, and 
 is capable of being reflected by glass mirrors, like 
 the light of the sun itself, the heat radiated by them 
 — unlike that of the solar beams — has neither the 
 power to traverse the transparent substance, nor is 
 it susceptible of being concentrated into a focus by 
 reflexion from a glassy surface. 
 
 Artificial heat, however, when at a very high tem- 
 perature , is found to have all the properties of solar 
 heat. Not only does it then admit of being focussed 
 by burning-glasses in the same manner as the sun- 
 beams, but the light emitted by it darkens solutions 
 of silver as effectually as the light of day ; so that 
 (as more recent experiments have proved) a photo- 
 graphic portrait can be taken as well by the rays 
 from coke at a white heat, as they can by the rays 
 of the sun itself. 
 
 But only those substances are capable of being 
 
 * The highest temperature of a good blast-furnace is, according 
 to Daniel, about equal to 3300°. This constitutes a “ high 
 white heat.” 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 225 
 
 rendered incandescent, which have power to sus- 
 tain the high temperatures requisite for ignition, 
 without being vaporized or decomposed by the 
 heat. Many bodies, however, are either dissipated 
 or destroyed long before they attain this intense 
 temperature ; while, on the other hand, those termed 
 combustibles, when heated in the air, burst into 
 flame , and undergo what is termed combustion . 
 
 “ Now what is combustion ? ” said Humphry to 
 himself, as he thought over the subject. “ What 
 are the phenomena which occur when substances 
 burn with the evolution of flame ? ” 
 
 The boy knew, that formerly it was supposed 
 bodies owed their combustibility to the presence of 
 a certain principle called “ phlogiston,” which 
 during combustion, said the philosophers, escaped 
 from them, producing light and heat ; whereas 
 when the bodies had lost their phlogiston — and 
 had become “ dephlogisticated,” as it was termed 
 — they ceased to be combustible. 
 
 Phlogiston, however, Humphry was well aware, 
 was a purely imaginary principle, of whose ex- 
 istence no proof had been given, and which had 
 been invented merely to explain a process that 
 appeared to be otherwise incomprehensible. 
 
 Moreover, Humphry had learnt from the books 
 he had already read upon the subject, that the 
 metals were increased in weight after being burnt . 
 so that it was impossible to attribute the combus- 
 
 Q 
 
226 
 
 THE AVONDERS OF SCIENCE. 
 
 tion in such cases to the escape of phlogiston, 
 since it was inconceivable Iioav a body could be 
 rendered heavier by losing something which had 
 previously been combined with it. 
 
 Nevertheless, the belief in this visionary phlo- 
 giston had continued for nearly half a century ; 
 and it was only in the year 177 o that more correct 
 views had been propounded concerning the process. 
 
 At the time of young Davy’s commencing the 
 study of this subject, Lavoisier’s new theory of 
 combustion had been in existence but a few years, 
 and the boy having obtained from Mr. Tonkin the 
 loan of the treatise in which the more correct 
 views were originally propounded, had eagerly 
 perused the volume, being not a little delighted 
 with the precision of reasoning and the boldness 
 of speculation contained in it. 
 
 Still Humphry was not satisfied with merely 
 reading and acquiring the ideas of others. He 
 criticised the theoretical speculations of the great 
 French philosopher, doubted, and rejected, and 
 advanced speculations of his own, while speculation 
 led him to experiment.* 
 
 * The above is Dr. Davy’s account of his brother’s first 
 chemical studies : — “ Such was the commencement of Humphry 
 Davy’s career of original research,” he adds, “which in a few 
 years, by a succession of discoveries, accomplished more in re- 
 lation to change of theory and extension of science than, in the 
 most ardent and ambitious moments of youth, he could either 
 have hoped to effect or imagined possible.” 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 227 
 
 Humphry began the investigation of the phe- 
 nomena of combustion by an experiment, to prove 
 that the air in which combustibles are suffered to 
 burn till they are extinguished undergoes a very 
 remarkable change. 
 
 For this purpose the lad put a little water in a 
 soup-plate, and on it he placed a small piece of 
 candle, so that it might swim on the surface. 
 Having lighted the wick he covered it over with 
 a large tumbler, and found that the candle then 
 burnt only for a short time, whilst immediately the 
 flame was extinguished the water rose in the tum- 
 bler considerably above its level in the soup-plate. 
 
 Hence it was evident, that the portion of the air 
 which was necessary for combustion had been 
 removed by the burning candle from the atmo- 
 sphere confined within the tumbler, and that, there- 
 fore, it was no longer capable of sustaining the 
 flame. 
 
 “ But maybe,” thought Humphry, “ the candle, 
 in burning, gives off some gas, which is preju- 
 dicial to combustion.” 
 
 So, to satisfy himself whether such were the 
 case or not, the boy burnt some charcoal in an old 
 iron saucepan, that he had previously drilled full of 
 holes, in order to admit the air. Then, having 
 fitted a tin tube into the lid of this, he, by means 
 of the chimney so formed, conducted the gas evolved 
 by the burning charcoal into a wide -mouthed bottle, 
 
228 
 
 THE WONDERS OF SCIENCE. 
 
 that he had previously filled and placed with its 
 mouth downwards, on a perforated stand in a pail 
 of cold water ; so that as the combustion went on 
 the gas produced kept bubbling up in the pail from 
 the end of the tube, and displacing the water as it 
 rose into the inverted bottle that stood imme- 
 diately above it. The arrangement, however, will 
 be more readily comprehended by reference to the 
 subjoined engraving : — - 
 
 As soon as sufficient gas had been collected 
 Humphry removed the tube from the pail, and 
 corked the bottle under water ; then having set 
 the bottle of gas on a table, he attached a piece o£ 
 candle to the crooked end of a long wire, and 
 lowering this, while alight, into the gas, found, to 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 229 
 
 liis astonishment, that the flame was immediately 
 extinguished. 
 
 “ So then,” cried the delighted boy, “here is a 
 kind of air that I can neither see, nor feel, nor smell, 
 and yet it extinguishes burning bodies like water.” 
 
 But Humphry was too eager to examine the 
 properties of the gas he had collected to wait to 
 reflect upon the curious results it afforded him. 
 Accordingly he procured a tall glass jar, and having 
 placed a piece of burning candle at the bottom of 
 this, he proceeded to empty the gas from the bottle 
 into the jar, when to his surprise he discovered 
 that he could pour out the heavy air that had 
 come from the burning charcoal as though it had 
 been a liquid, while, immediately it fell upon the 
 lighted candle at the bottom of the jar, the flame 
 disappeared as suddenly as if so much water had 
 been showered upon it. 
 
 After this the boy amused himself by decanting 
 the gas backwards and forwards from one vessel 
 to the other, and ultimately found that it was 
 instantaneously fatal to animals, destroying sen- 
 tient life as rapidly as it extinguished burning sub- 
 stances. 
 
 Humphry’s next step was to discover what sub- 
 stance was capable of readily absorbing this gas, 
 and after many trials he found that lime-water did 
 so with great facility. 
 
 Accordingly he added about an ounce of quick- 
 
230 
 
 THE WONDERS OF SCIENCE. 
 
 lime to a quart of water in a glass bottle, and 
 corking it up closely he shook it several times, 
 so as to dissolve as much of the lime as possible ; 
 after which he allowed it to settle, and then de- 
 canted off the transparent and colourless liquid 
 into a clean bottle with a glass stopper. This 
 transparent solution of lime in water he then 
 poured into the glass jar containing the gas from 
 the burning charcoal, and having corked the vessel 
 tightly up, he shook it about, and immediately per- 
 ceived that the lime-water was rendered turbid by 
 the gas, being no longer clear and transparent as be- 
 fore, but changed to an opaque milky white ; then 
 having filtered the turbid water, and so separated 
 from it all the white particles that had rendered 
 the solution opaque, he dried and weighed the sedi- 
 ment, and found that the quantity of lime which had 
 been dissolved by the water had become nearly 
 doubled in weight by the gas which it had absorbed. 
 
 The youth had now learned how to remove the 
 products of combustion, and he was consequently in 
 a position to determine whether the air, after a 
 substance had been burned in it, really had or had 
 not been deprived of anything during the process. 
 
 Humphry therefore placed a small quantity of 
 lime-water at the bottom of a wide-mouthed bottle, 
 and through the cork of this he passed one end of a __ 
 long wire, while to the other end of it he attached 
 a small piece of wax taper. This he lighted, and 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 231 
 
 then lowered down into the air that stood above the 
 lime-water in the vessel. The cork was now forced 
 tightly into the mouth of the bottle, and in a 
 minute or two the taper was extinguished. After 
 this the jar was shaken well up, when the youth 
 beheld, to his great delight, the lime-water rendered 
 turbid by the gas evolved during the burning of the 
 taper. 
 
 The next step was to discover whether the air 
 which remained in the bottle (and from which the 
 products of the burning taper had been removed 
 by the lime-water) was still capable of sustaining 
 combustion. 
 
 Accordingly another lighted taper was lowered 
 into it, but this was as rapidly extinguished as the 
 one had been by the gas from the burning charcoal 
 itself. It was afterwards found, too, that that part 
 of the air which remained after combustion was as 
 destructive of animal life as even the charcoal gas 
 had been discovered to be. 
 
 “ How wonderful ! ” exclaimed the boy, “ that 
 the atmosphere round about us should be made up 
 of two different kinds of air, — one that enables 
 combustibles to burn and animals to live in it, while 
 the other immediately extinguishes flame and de- 
 stroys sentient life ! How can I collect that portion 
 of the air which supports combustion and maintains 
 life, apart from that which puts an end to it ? I 
 should like to see what it would do by itself, and 
 
232 
 
 THE WONDERS OF SCIENCE. 
 
 whether substances would burn brighter in it alone ; 
 for surely such must be the case, since in the atmo- 
 sphere it is mixed with another kind of air that 
 extinguishes flame and destroys living creatures, so 
 that the one must constantly be counteracting the 
 effects of the other.” 
 
 Humphry racked his brains for a long time for 
 the means whereby to separate the two kinds of air 
 from each other. At last he remembered one of 
 Lavoisier’s experiments in connexion with the 
 subject, and immediately set to work to repeat it. 
 
 With this view the lad obtained some “ calcined 
 mercury,” for this substance he knew to have been 
 produced merely by burning metallic mercury for a 
 long time in a tube exposed to the air, so that the 
 portion of the atmosphere which supported com- 
 bustion (instead of being evolved in a gaseous form, 
 as in the case of the burning charcoal) had become 
 fixed , or rendered solid , in the “calx” which resulted 
 from the process. The boy was therefore anxious 
 to see whether it were not possible, by burning the 
 calcined product once more, to drive off that portion 
 of air which had been taken up by it during the 
 previous burning, and so to discover what are the 
 peculiar and distinctive properties of the air which 
 had been absorbed. Consequently, he submitted 
 some of this calcined mercury to a red heat in a 
 retort, and collected the gas that was given off from 
 it in a wide-mouthed bottle from which he had cut 
 
THE 'WONDERFUL EFFECTS OF HEAT. 
 
 233 
 
 off the bottom. This, having corked, he filled 
 with water, and stood on a perforated ledge in a 
 pail — the gas being collected as before described. 
 When the water had all been displaced from the 
 bottle, and it was consequently full of gas, Hum- 
 phry slid it, while under the water, off the ledge 
 into a soup-plate, and then, removing it to a table, 
 proceeded to investigate its properties. 
 
 Here, then, he had a jar-ful of the gas (named 
 oxygen by chemists) that maintained the com- 
 bustion of bodies in the open air, and separate, f oo, 
 from the other gas, which tended rather to retard 
 their burning in the atmosphere. 
 
 Humphry’s first experiment Tvas to introduce into 
 the gas thus obtained a lighted taper, placed at 
 the end of the wire as before, and the boy was 
 enraptured as he beheld the flame immediately en- 
 large (instead of diminishing, as when confined in a 
 jar of mere atmospheric air), and become intensely 
 bright, while the combustion proceeded at so rapid 
 a rate that the piece of taper itself was soon con- 
 sumed. Then another piece of taper was used, but 
 this was blown out immediately after being lighted, 
 so that the wick was merely glowing on its intro- 
 duction into the gas. On being plunged into the 
 jar, however, it was instantly re-kindled, and burst 
 mto the same vivid flame as before. 
 
 Next, the combustion of sulphur was tried in 
 the gas. This substance burns in the open air, 
 
234 
 
 THE WONDERS OF SCIENCE. 
 
 as is well known, with a small blue flame. On 
 placing a small piece of lighted sulphur, however, 
 in a copper capsule attached to the end of a long 
 wire, it was no sooner lowered into the jar than it 
 began to burn with a beautiful purple or lilac- 
 coloured light, the flame becoming suddenly en- 
 larged, and the sulphur itself appearing to dissolve 
 in the gas. At the conclusion of the experiment 
 the water in the soup-plate, in which the jar 
 stood, was set carefully on one side, for after-exa- 
 mination. 
 
 After this the lad tried the combustion of 
 phosphorus in another jar of gas, in the same 
 manner. Humphry knew the combustion of this to 
 be very vivid, even when inflamed in the atmo- 
 sphere ; so, to prevent accidents, he used in the jar 
 a piece not larger than a pea : but even this, when 
 lowered alight into the gas, produced so intensely 
 white a flame that he could scarcely bear to look at 
 it, while clouds of white flaky matter were evolved 
 from it like smoke ; the heat, too, was so great, 
 that he was afraid the jar would crack : and so it 
 would have done, had he not, luckily, employed a 
 very large one. 
 
 The young experimentalist was overjoyed at the 
 splendour of the combustion of these substances, 
 and longed to see whether it were possible to burn 
 the metals by such means. So, having made ano- 
 ther jar-ful of the same gas, and placed it over 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 235 
 
 some water in a soup-plate, he took a piece of watch- 
 spring, and when he had affixed the sulphur tip of 
 a match to the end of this, he lighted the match 
 and plunged the whole into the gas. He was soon 
 well repaid for his pains ; for in a short while the 
 metal burst into vivid combustion, throwing off a 
 shower of the most brilliant sparks, which played 
 around it like a fountain of fire, whilst goutes of the 
 white-hot metal fell hissing through the water, and 
 lay beneath it for some time, red hot upon the 
 plate, the glaze of which was afterwards found to 
 have been even fused at the points where the 
 molten iron had fallen upon it. 
 
 But the boy’s rapture on beholding the wonder of 
 combustible iron was not altogether unmingled with 
 fear ; for the heat produced by the burning of the 
 metal was so intense, that he grew nervous lest the 
 glass jar should break during the experiment. He 
 was wise enough, however, to hold it in his hand, 
 so as to allow a little of the gas to escape, as well as 
 to prevent the jarring of the glass on the plate 
 beneath. 
 
 Humphry was now nearly exhausted with his 
 labours, and it was time to reflect upon all that had 
 occurred. 
 
 In the first place, then, it was certain that a consi- 
 derable quantity of the gas used in these experiments 
 had disappeared during the combustion, for the 
 water had each time risen in the jar above the level 
 
23G 
 
 THE WONDERS OF SCIENCE. 
 
 of that in the soup-plate. “ What, then, had become 
 of the lost gas ?” he asked himself. There was but 
 one answer, — It had combined with the burning 
 body, and formed a new substance with it. In the 
 case of the burning sulphur, the water that had 
 been in the soup-plate below the jar was found, 
 on examination, to be sour to the taste, and to 
 redden vegetable -blue colours ; so that here the gas 
 had combined with the combustible and produced 
 an acid that was soluble in water. Again, with 
 the burning phosphorus, the white flakes that bad 
 been evolved during the combustion had been 
 ultimately dissolved by the water, which likewise 
 tasted sour, while it stained vegetable colours in the 
 same manner as the sulphur product did ; whereas, 
 in the case of the burning iron, the metal appeared 
 to have been rusted, for the particles remaining at 
 the bottom of the soup-plate were found, after the 
 experiment, to have lost their metallic nature, and 
 to have assumed all the character of a “ calx,” or 
 rust. 
 
 “ Well, then,” said the lad, “ it seems that 
 during combustion one part of the air combines 
 with the burning bodies, and so either rusts or 
 acidifies them.” In confirmation of this view, he 
 recollected “ that the gas evolved from the burning 
 charcoal also gave a slightly sour taste to the_ 
 water it passed through.” 
 
 “ Still,” mused Humphry, “ if a part of the air 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 237 
 
 really does combine with the combustible burning 
 in it, the result, of course, should be, that the com- 
 bustible, after being burnt, should be heavier than 
 before — even as the lime with which I absorbed 
 the gas from the burning charcoal became greatly 
 increased in weight by it.” 
 
 The youth was not long in putting this part of 
 the matter to a practical test. Having accurately 
 weighed a small quantity of calcined mercury 
 (which, as we said before, he knew to be a rust of 
 the metal), he set to work again to make it red hot, 
 and to drive off the air with which it had previously 
 been made to combine while burning. This gas he 
 collected in a small glass jar, open at the bottom, 
 and having a stop-cock at the top of it. Then the 
 boy took a thin hollow ball of glass, which had also 
 a stop -cock fitted to it. Having screwed this on to 
 the metal plate of his air-pump, he exhausted the 
 glass ball as entirely of air as he could, and then 
 closing the cock he detached it from the pump, and 
 proceeded to ascertain the weight of the ball now 
 that it was divested of air. This done, Humphry 
 screwed the stop -cock of the glass ball on to that 
 of the glass jar in which he had collected the gas 
 from the calcined mercury ; then, turning on both 
 the cocks, the gas rose from the jar into the ball, 
 and when the jar itself was full of liquid, and all 
 the gas had consequently been removed from it, he 
 closed the stop-cock once more, and, unscrewing 
 
238 
 
 THE WONDERS OF SCIENCE. 
 
 the glass ball from the jar, proceeded to ascertain 
 how much the ball had gained in weight, now that 
 it contained the whole of the gas evolved from the 
 calcined mercury. 
 
 The next step was to weigh the mercury itself. 
 This, however, was no longer the red powder that 
 it was before the gas had been driven off from it, 
 but had now become “ reduced” into so much bright 
 liquid metal; and on being put into the scales it 
 was found to have lost just as many grains in weight 
 as the gas, which had been collected from it, required 
 to balance it in the scales. 
 
 But this was not enough to satisfy the cautious 
 young experimentalist, for he still desired to see 
 whether, if the same quantity of metallic mercury 
 were burned in the same quantity of gas, the re- 
 sulting compound of the metal and the air would 
 weigh exactly as much as the air and the metal did 
 separately. 
 
 Accordingly, Humphry proceeded now to burn 
 the metallic mercury in the gas, and so to cause 
 them to combine once more. By keeping the metal 
 at a red heat with the gas above it, the combination 
 was at length effected, and then, on weighing the 
 red “ calx,” or rust, that resulted from the process, 
 it was ascertained to be precisely as heavy as the 
 metal and the gas had weighed when separate. 
 
 Here, then, it was manifest that substances by 
 burning were increased in weight , and that they 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 239 
 
 were just as much heavier after combustion as the 
 weight of the quantity of air which had been ab- 
 sorbed by them during the process. 
 
 “ Is it true, therefore,” mused the boy, “ that the 
 candle and the coals, which appear to us to be de- 
 stroyed by combustion, become positively increased 
 in weight by it ? ” 
 
 The experiment which Humphry had already 
 performed in collecting the gas from burning char- 
 coal assured him that such was positively the case, 
 for he knew that this gas, though invisible, had an 
 absolute weight, being so much heavier than the 
 atmosphere that it admitted of being poured, like 
 water, from one vessel to another. The experiment 
 with the calcined mercury, moreover, told him, that 
 if he had weighed the charcoal before it was burnt, 
 as well as the quantity of air which it had con- 
 sumed while burning, he would have found the 
 whole of the gas which resulted from the com- 
 bustion would have been precisely as heavy as the 
 air and the charcoal added together. 
 
 For the same reason, if the gases evolved from a 
 burning candle were to be collected, they, likewise, 
 would be found to be heavier than the candle itself; 
 and just as much heavier, too, as the quantity of 
 air which had disappeared during the combustion. 
 
 Combustion , therefore , was merely the rapid 
 combination of a portion of the air with a com - 
 
240 
 
 THE WONDERS OF SCIENCE. 
 
 bustible body , accompanied with the evolution of 
 heat and light . 
 
 Still Humphry could not quit the subject without 
 examining the conditions which were necessary to 
 produce such a combination. The principal re - 
 quisite was manifestly elevation of temperature . 
 
 Some substances, however, inflame at ordinary 
 temperatures — immediately on entering the atmo- 
 sphere — as, for instance, the gas called “ phos- 
 phuretted hydrogen .” This was a new discovery 
 in young Humphry’s time, and the boy delighted to 
 produce the gas by heating a small quantity of 
 phosphorus in a retort completely filled with, a 
 moderately strong solution of caustic potash — the 
 heat being carefully applied until the solution boiled, 
 while the beak of the retort was kept under the 
 shelf of a water- bath. Upon coming into contact 
 with the air, Humphry saw the bubbles of gas, as 
 they left the surface of , the water, suddenly inflame, 
 with a slight explosion ; and as the atmosphere was 
 still, each bubble, on bursting, produced a beautiful 
 expanding ring of white smoke. 
 
 It is this gas which gives rise to the production 
 of those lights in the air which are known by the 
 names of “ ignes fatuif (“ will-d* -the-wispsf or 
 “ Jack- o' -lanterns ,”) and “ corpse-candlesf — the 
 former appearing over marshes, and the latter being 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 241 
 
 seen to rise from recent graves — but both alike pro- 
 ceeding from the decomposition of organic matter.* 
 
 Again, phosphorus dissolved in sulphuret of 
 carbon produces a spontaneously inflammable so- 
 lution ; so that if a small quantity of the liquid be 
 poured on a piece of paper it evaporates rapidly, 
 and leaves the phosphorus behind, which imme- 
 diately bursts into flame. 
 
 The same phenomenon of spontaneous combus- 
 tion also occurs with the substance called “ pyro- 
 phorus .” This is generally formed of powdered 
 
 alum heated, with an equal weight of brown sugar 
 or honey. After the materials have been melted 
 and well mixed in an iron ladle, they are made 
 red hot in a phial coated with clay, and placed in 
 a crucible rf sand — the heating process being con- 
 tinued until a blue flame appears at the mouth of 
 the bottle ; this is allowed to burn for about five 
 minutes, when the phial is well stopped and re- 
 moved from the fire. 
 
 The compound, on being cooled and exposed to 
 the air, is spontaneously combustible. 
 
 Sulphate of potassa , likewise, when heated to 
 redness with half its weight of lamp-black, also 
 forms a compound, which takes fire immediately on 
 exposure to air. 
 
 * A chemical philosopher in America ignited a piece of paper 
 by one of these lights on a still night. The breath, however, had 
 to be held during the operation, for the least agitation of the air 
 wafted them from the spot. 
 
 R 
 
242 
 
 THE WONDERS OF SCIENCE. 
 
 Again, tartrate of lead , heated to a dull red in a 
 glass tube, forms, when cool, a very perfect pyro- 
 phorus, which immediately inflames on being shaken 
 out into the atmosphere. Further, when iron is in 
 a state of extreme mechanical division — such as 
 very fine powder — its affinity for the oxygen of the 
 atmosphere is such that it heats, and even ignites, 
 on exposure to the air. This is the case with the 
 finely-divided metal as obtained by the action of 
 hydrogen gas upon red-hot iron-rust, so that, when 
 suffered to cool in this gas, the iron is as spon- 
 taneously oxidizable as even potassium itself 
 
 Moreover, if a small piece of spongy platinum be 
 held in a jet of hydrogen, issuing from a small tube 
 into the atmosphere, the platinum immediately be- 
 comes red hot, while the gas itself bursts into 
 flame. 
 
 Platinum wire , or foil , if the surface be per- 
 fectly clean, acts so rapidly at common tempera- 
 tures on a mixture of oxygen and hydrogen gases 
 (mixed in the proportion of 1 to 2), that it often 
 becomes red hot on being introduced into a vessel 
 containing them, and kindles the mixture. Hand- 
 ling the platinum, however, wiping it with a towel, 
 or exposing it to the atmosphere for a few days, 
 suffices to soil the surface of the metal, and so to 
 prevent its action. 
 
 Finally, a piece of the metal called potassium 
 (procured from potash) has so strong an affinity for 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 243 
 
 oxygen, that when thrown upon water, at ordinary 
 temperatures, the metal decomposes it the instant 
 it touches the liquid, and so much heat is dis- 
 engaged that the potassium is inflamed, and burns 
 vividly while swimming on the surface. The same 
 spontaneous combustion ensues, indeed, with ice — 
 so that the cold body appears to heat the metal 
 even to inflammation. 
 
 But a still more curious instance of spontaneous 
 inflammation is to be found in the sudden explosion 
 of a mixture of Chlorine and Hydrogen gases when 
 exposed to sunshine; for though the two gases, 
 when mixed together in equal volumes, may be 
 preserved without change in a dark place for any 
 length of time, nevertheless, immediately they are 
 submitted to the direct solar rays, the whole mix- 
 ture becomes suddenly inflamed, and a violent ex- 
 plosion ensues. 
 
 Next to those substances which are spontane- 
 ously combustible comes phosphorus , which in- 
 flames, when perfectly dry, at the low tempera- 
 ture of 60°. Indeed, such is its tendency to combine 
 with the air, that, if free from all moisture, it takes 
 fire by the heat of the hand alone. Slight friction, 
 as when rubbed upon a piece of coarse paper, also 
 produces the same result. It is very difficult, how- 
 ever, to light a piece of paper by the flame of 
 phosphorus, for the paper becomes coated with 
 a crust of the solid phospho ous acid , which is pro- 
 
244 
 
 THE WONDERS OF SCIENCE. 
 
 duced by the combustion, and serves to protect it 
 from the flame. 
 
 There is, likewise, a gas (for the knowledge of 
 which we are indebted to the after-discoveries of 
 Davy himself), called protoxide of chlorine , which 
 requires so slight an elevation of temperature to 
 decompose it, that even the heat of the hand is 
 sufficient to cause it to explode with the evolution 
 of heat and light. This gas is produced by the 
 action of hydrochloric acid on chlorate of potash 
 and water, and it is so explosive that it fre- 
 quently detonates violently in being transferred 
 from one vessel to another, It should, therefore, 
 be dealt with by none but experienced chemists. 
 A small piece of phosphorus let up into it instantly 
 takes fire, and burns with much brilliancy. Sul- 
 phur likewise decomposes it with violent detona- 
 tion, and even a piece of blotting-paper introduced 
 into the gas is sufficient to cause it to be suddenly 
 resolved into its elements. 
 
 The gas termed Binoxide of Chlorine (called 
 also the Peroxide') is even more explosive than the 
 Protoxide. It detonates violently when heated to 
 212°, emits a strong light, and undergoes a greater 
 expansion than the simple oxide above described. 
 
 Again, the Binoxide of Hydrogen (or Peroxide , 
 as it is sometimes denominated), when heated to 
 212°, gives off oxygen so rapidly as to cause an 
 explosion, while the rusts (oxides) of some of the 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 245 
 
 metals act upon it with such energy, that, when 
 dropped into it, a violent detonation immediately 
 ensues, and the glass tube on which the experiment 
 is conducted becomes red hot. 
 
 Further, the gas called Binoxide of Nitrogen , 
 when combined with sulphurous acid gas, pro- 
 duced a compound called Nitro- sulphuric Acid, 
 which is so prone to decomposition that it cannot 
 be collected in a separate state, and the salts of 
 which are held together with such slight affinity 
 that even a little charcoal powder, or spongy plati- 
 num, is sufficient to cause a violent evolution of gas, 
 while at a temperature only a few degrees above 
 that of boiling water, an explosion ensues. 
 
 Moreover, the Bisulphuret (called, also, the Per- 
 sulphuret) of Hydrogen , which is a yellow oil-like 
 liquid, has its elements so feebly united, that at 
 a heat short of 212° it is instantaneously resolved 
 into sulphur , and the simple Sulphuretted Hydro- 
 gen which is evolved, in the form of gas, with 
 almost explosive violence. The same effect is pro- 
 duced by the mere contact of most substances — 
 especially the metals, flint, and even the earths in 
 powder — while the oxides of gold and silver are 
 “ reduced” by it with such energy that they are 
 rendered instantaneously red hot. 
 
 These binary compounds of oxygen or sulphur 
 have most of them been discovered since Davy’s 
 time. They are, however, remarkable in possessing 
 
246 
 
 THE WONDERS OF SCIENCE. 
 
 kindred affinities, and being severally decompo- 
 sible at a temperature of 212°. 
 
 After these, in the order of ready decomposi- 
 bility, come the compounds of Nitrogen . 
 
 The peculiar black powder, called by chemists 
 iodide of nitrogen , which is produced by pouring 
 some strong ammonia upon a very small quantity 
 of iodine, is so explosive, that it detonates violently 
 as soon as it is dried ; and the slightest pressure, 
 even when moist, produces a similar effect. If 
 put into pure ammonia, it explodes when lightly 
 pressed in that liquid. Heat and light are emitted 
 during the detonation, which is merely a species of 
 instantaneous combustion. So dangerous is this 
 compound, that the most experienced chemists 
 seldom operate on more than a few grains of iodine 
 at once. 
 
 The yellow oil-like liquid, called chloride of ni- 
 trogen, which results from the action of chlorine gas 
 upon sal ammoniac, also enters into instantaneous 
 combustion at very low temperatures ; so that, 
 when it is heated to a little above 200°, it detonates 
 with tremendous violence, a vivid flash of light 
 being produced at the same time, while the vessel 
 — which, to prevent accidents, is covered with a 
 wire cage — is broken to atoms. This compound is 
 so dangerous, being one of the most explosive sub- 
 stances yet known, that in dealing with it the face 
 is always protected by a mask, and only a small 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 247 
 
 globule of it, no larger than a mustard seed, ex- 
 perimented upon. Dulong, the French chemist 
 who discovered it, lost an eye and the use of a 
 finger whilst operating with it ; and Davy him- 
 self, in after-life, was wounded in the face by the 
 effects of its detonation. The mere contact of this 
 substance with certain combustibles causes it to 
 explode violently, even under water, at ordinary 
 temperatures. If touched with phosphorus, india 
 rubber, common oil, turpentine, caustic potash, or 
 even soap, it detonates so violently as to break to 
 pieces the vessel containing it, and to scatter the 
 water in which it is immersed in a shower all 
 around. 
 
 Bromide of nitrogen , again, is said to be even 
 more easily decomposed than the chloride. It is a 
 dark -red oily liquid, having a foetid odour, and 
 giving off a vapour that is very irritating to the 
 eyes. This compound, when touched with phos- 
 phorus, or even a small piece of arsenic, detonates 
 with tremendous violence. 
 
 Next to the ' above remarkable compounds of 
 Nitrogen, the fulminates of the 'precious metals 
 (into the composition of which, however, Nitrogen 
 also enters) must be ranked in the order of ready 
 combustibility ; for these likewise explode at very 
 low temperatures, with the production of heat and 
 light. 
 
 First come the Nitrurets of Mercury and Silver 
 
248 
 
 THE WONDERS OF SCIENCE. 
 
 — that is to say, compounds of those metals with 
 Nitrogen. These are formed by the action of Am- 
 monia on the oxide of Mercury or Silver. The 
 Nitruret of Silver explodes with tremendous vio- 
 lence when gently rubbed or heated, and the Ni- 
 truret of Mercury when struck with a hammer, or 
 acted upon by strong oil of vitriol. 
 
 Fulminating Gold , when suddenly heated to 
 about 290°, detonates with great force and a 
 vivid flash ; and if exploded upon platinum foil, 
 the metal is torn at the point of contact. Friction 
 with hard bodies, or an electric shock, also ex- 
 plodes it. The more it is washed and dried, the 
 more explosive this compound becomes ; and if 
 long retained at the temperature of boiling water, 
 so as to become perfectly dry, the slightest friction 
 causes it to detonate immediately and violently. 
 If it be moist, however, it does not explode on 
 the application of heat till dried, and those portions 
 which first become dry explode the soonest ; so 
 that, in such a case, a succession of detonations is 
 produced. 
 
 Fulminating Mercury requires a temperature 
 of 300° to cause it to explode, which it then does 
 with a bright flame. It also detonates by friction, 
 so that the greatest caution is required in pre- 
 paring and dealing with it. This compound has 
 even been known to explode in a moist state, and 
 in the most careful and skilful hands it cannot 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 249 
 
 be touched without considerable danger.* This 
 is the substance used in percussion caps ; it is 
 introduced into the caps moistened with a little 
 tincture of benzoin, so as to be dropped into them, 
 and then carefully dried. Howard, the discoverer 
 of the compound, endeavoured to substitute it for 
 gunpowder, but the explosion was found to be so 
 sudden that it burst the gun without expelling the 
 shot. 
 
 Fulminating Silver likewise explodes, with the 
 evolution of light and heat, at nearly the same low 
 temperature. A grain, or merely half a grain of 
 this substance, detonates with great violence, when 
 heated or when touched with any hard body. On 
 being placed upon a piece of rock crystal, and 
 rubbed in the slightest manner by another crys- 
 tal, it explodes with great force. It has some- 
 times exploded upon the contact of a glass rod, 
 even under water ; so that merely the feather of 
 a common quill is generally used to collect it. It 
 is dangerous to keep it in a cork-stoppered phial, 
 
 * A melancholy proof of this was furnished by the death of 
 Mr. Hennell (the chemist at Apothecaries’ Hall) on the 4th June, 
 1842. He was in the act of mixing two separate portions of 
 the powder in a moist state with an ivory knife, when the whole 
 quantity, amounting to above 61bs. exploded, and shattered his 
 head, breast, and right arm to atoms. A man, however, who 
 was standing within four yards of him, was not injured, but the 
 windows of the surrounding buildings were broken ; while a 
 large wooden block, upon which one of the basins was placed, 
 was shivered, as was also the pavement on which it stood. 
 
250 
 
 THE WONDERS OF SCIENCE. 
 
 for serious accidents have arisen from its unex- 
 pected explosion in a confined state. In short, 
 persons cannot be too careful in meddling with it, 
 and its use for detonating balls and other purposes 
 of amusement is highly perilous and reprehensible. 
 
 Fulminating Platinum , on the other hand, ex- 
 plodes at a temperature of 420° with a loud re- 
 port. 
 
 There is likewise a fulminating powder , com- 
 posed of a mixture of 3 parts nitre with 1 of sul- 
 phur, and 2 of dry carbonate of potash . This 
 substance explodes with much violence at the low 
 temperature of 330° ; so that if a little of the com- 
 pound be heated up to that point upon a metallic 
 plate, it blackens, fuses, and detonates with great 
 force. 
 
 Again, a mixture of 3 parts chlorate of potash 
 and 1 of sulphur detonates loudly when struck 
 upon an anvil with a hammer, and even sometimes 
 explodes spontaneously. If 2 or 3 grains of chlo- 
 rate of potash be reduced to powder in a mortar, 
 and some very fine flour of brimstone be then 
 added to it, the two substances, when rubbed to- 
 gether, will detonate with a smart noise, like the 
 cracking of a whip. A mixture of chlorate of 
 potash and sulphuret of antimony takes fire by 
 gentle trituration, and deflagrates with a bright puff_ 
 of flame and smoke. Chlorate of potash was pro- 
 posed by Berthollet (the French chemist) as a 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 251 
 
 substitute for nitre in gunpowder. The attempt 
 was made at Essone, in 1778 ; but no sooner was 
 the mixture of the chlorate with the sulphur and 
 charcoal submitted to trituration than it exploded 
 with violence, and proved fatal to several persons. 
 
 With 'phosphorus and chlorate of potash the 
 explosion is dangerously violent : 1 grain of phos- 
 phorus with two of the chlorate, if placed in a 
 small piece of paper and struck with a hammer 
 upon an anvil, will immediately explode, and the 
 phosphorus be thrown about in an inflamed state. 
 Gunpowder, again, if mixed with powdered glass 
 and struck with a heavy hammer upon an anvil, 
 almost always explodes. 
 
 Moreover, a mixture of oxygen and hydrogen 
 gases , suddenly submitted to violent mechanical 
 compression, unite with a vivid flash of light and 
 produce water. 
 
 Next to Phosphorus and the Fulminates, Sul- 
 phur is the most easily kindled. This body enters 
 into combustion at about 500°. It is the compara- 
 tively low temperature at which sulphur bursts into 
 flame, that makes it so important an ingredient 
 in gunpowder, matches, &c. The easy combus- 
 tibility of sulphur may be well illustrated by pro- 
 pelling a small quantity of it in powder into the 
 current of hot air issuing from the glass chimney 
 of a gas lamp, when it will be seen to take fire at a 
 considerable height above the flame. 
 
252 
 
 THE WONDERS OF SCIENCE. 
 
 Wood , cotton , paper , &c. require, on the other 
 hand, their temperatures to be raised much higher 
 than that required for the inflaming of sulphur, 
 in order to be made to enter into combustion.* 
 Paper merely becomes brown or scorched at the 
 heat of 440°, nor can it be lighted at a red heat, 
 though the temperature of this is 1OOO 0 . Cotton 
 or tow, however, when greased with oil, occasionally 
 absorbs air so rapidly, and produces so much heat 
 during the process, that spontaneous combustion 
 
 * In the ordinary lucifer-match (an invention since Davy’s 
 time) we have a striking illustration of the different temperatures 
 required for various substances to enter into combustion. The 
 phosphorus with which these lucifers are tipped becomes in- 
 flamed at a very low heat (60°) , so that mere friction is sufficient 
 to ignite it. This substance, in burning, produces heat sufficient 
 to kindle the sulphur next to it ; for this, as we have seen* 
 enters into combustion at about 500° ; and the sulphur again, 
 in burning, raises the temperature sufficient to ignite the wood, 
 which requires a heat of at least 1000° before it can be made to 
 burn. Had the match been tipped with phosphorus alone, the 
 phosphorous acid produced by the combustion would have in- 
 crusted the wood and prevented it inflaming. Before the use of 
 phosphorus matches had become general, others were introduced, 
 the tips of which were coated with a mixture of chlorate of potash 
 and sulphur, and these had to be drawn forcibly through a piece 
 of folded sand-paper, for this mixture requires a much higher 
 heat in order to inflame it. Previous to the introduction of 
 these, again, the common brimstone match was in general use. 
 This, as is well known, was kindled by means of a spark in 
 tinder — the tinder consisting of charred rag, and the spark, there- 
 fore, being merely a particle of charcoal at a red heat, while 
 the ignition of the tinder itself was originally produced by the 
 percussion of a piece of flint and steel, which evolved so much 
 heat that small splinters of the metal were fused by it and fell 
 upon the tinder in a red-hot state. 
 
THE WONDERFUL EFFECTS O HEAT. 
 
 253 
 
 frequently occurs from this cause. The same effect 
 sometimes arises from hay being stacked before 
 being perfectly dry; the moisture sets up a kind of 
 fermentation in the interior of the stack, and this 
 evolves so much heat that the temperature becomes 
 raised to the point required for the material to 
 enter into rapid combination with the atmosphere, 
 so that spontaneous combustion is the result. 
 
 Again, there are certain mixtures of gases which 
 are explosible at a red heat, while others cannot 
 be made to enter into combustion at that tem- 
 perature, but require the presence of flame in order 
 to fire them. 
 
 Carhuretted hydrogen ( coal gas), sulphuretted 
 hydrogen , and carbonic oxide , can be made to in- 
 flame in air by red-hot iron or charcoal ; and a 
 mixture of oxygen and hydrogen gases can be ex- 
 ploded by a red heat visible in daylight, whereas a 
 dull red heat only causes the two gases to combine 
 silently without detonation. Fire-damp , however, 
 (which is light carburetted-hydrogen gas, and the 
 same as that which rises from stagnant pools on 
 disturbing the mud at the bottom), cannot be 
 inflamed by the strongest red heat; so that a fire 
 made of charcoal, that will burn without flame, 
 may be blown up to whiteness without exploding 
 a mixture of this gas with air. A piece of iron 
 also, at the highest degree of red heat, and even at 
 an ordinary white heat, does not inflame an ex- 
 
254 
 
 THE WONDERS OF SCIENCE. 
 
 plosive mixture of fire-damp, but when brought 
 to its highest point of white heat, iron immediately 
 causes the fire-damp to combine with the air with 
 a violent detonation. 
 
 The knowledge of this fact, which we owe to 
 the researches of Davy himself, was of immense 
 importance in the construction of the safety -lamp, 
 and, once discovered, it was treasured in the brain 
 for after use, for the preservation of life and the 
 mitigation of suffering. 
 
 Again, there are some substances which are so 
 readily inflammable that they take light even at 
 the approach of dame. These bodies consist of 
 highly vaporizable liquids, such as alcohol , ether , 
 naphtha , sulphur et of carbon , oil of turpentine, &c. 
 From the tendency of these combustible liquids to 
 pass into vapour, the surrounding atmosphere (im- 
 mediately on opening any vessels containing them) 
 becomes charged with their fumes, so that an almost 
 explosive mixture is formed with the air; and as 
 this extends to some distance from the liquid itself, 
 the approach of a lighted body instantaneously 
 causes the whole volume of vapour to pass into one 
 sheet of flame — an effect which is occasionally at- 
 tended with the most disastrous results. 
 
 On the other hand, some combustible liquids re- 
 quire their temperatures to be highly raised before 
 they can be inflamed ; such is the case with the 
 common fixed oils, — as lamp -oil, and others. For 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 255 
 
 this purpose a cotton wick is usually employed in 
 burning them, so that, by the capillary attraction 
 of the fibres, a small portion of the liquid may be 
 raised above the level of the rest, and the oil thus 
 be brought into connexion with the flame by 
 minute quantities at a time ; the consequence 
 being that, as each small portion of the liquid is 
 heated, it is converted into vapour, or gas, — and 
 this, by the high temperature maintained by the 
 burning wick, is made to enter into combustion 
 with the surrounding air, and so to be continually 
 inflamed above it. Any porous substance which is 
 a bad conductor of heat (such as Bath -brick or 
 sandstone), will, if cut to a fine edge, answer 
 all the purposes of the ordinary cotton lamp-wick ; 
 for if a light be applied to this, so as to raise its 
 temperature sufficient to convert into gas the film 
 of oil at the summit, the fluid will be readily in- 
 flamed, and continue burning until such an in- 
 crustation of charcoal ensues at the tip, as to pre- 
 vent the oil being heated any longer by the flame. 
 
 Further, some substances cannot be made to 
 burn at ordinary temperatures in the open air, 
 though, on being confined in a vessel of oxygen 
 gas, they readily enter into combustion when their 
 temperature is raised. This is the case, as we have 
 seen, with iron, and some of the other metals. 
 
 The next problem to be resolved was, Whence 
 
256 
 
 THE WONDERS OF SCIENCE. 
 
 come the light and heat that are emitted during 
 the process of combustion ? 
 
 “ All cases of combination with oxygen,” mused 
 the youth, “ such as the rotting of wood, and the 
 gradual rusting of metals in the open air, are, pro- 
 bably, attended with the evolution of heat ; but 
 in such instances the process is so slow, that the 
 heat evolved is unobserved, and dissipated without 
 accumulation. When the combination, however, 
 takes place in a shorter time, as in the production 
 of vinegar, the heat becomes proportionately sen- 
 sible ; and when the combination with the oxygen 
 is so rapid that the whole of the heat is evolved in 
 a much more limited period, as during combustion, 
 the increase of temperature is rendered consider- 
 ably more intense. A pound of charcoal, for 
 instance, combining with oxygen in the process of 
 respiration, gives off the same amount of heat as it 
 does when in a state of ignition, and takes up pre- 
 cisely the same quantity of the gas. In the one 
 case, however, the combination is spread over 30 
 hours, whereas in the other it occupies but as 
 many minutes.” 
 
 Humphry reflected for a long time as to the 
 origin of the light and heat evolved during the 
 burning of substances. 
 
 “Are the light and heat,” said he to himself, 
 “ originally imprisoned, as it were, in the com- 
 bustible, and set free during the burning of it ? 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 257 
 
 or are they merely the result of the rapid and 
 energetic combination of the oxygen of the air with 
 the burning substance 
 
 The former assumption the boy knew to be La- 
 voisier’s theory of the subject, but such an expla- 
 nation appeared to him to be inconsistent with the 
 facts. 
 
 The 'products of combustion are not always the 
 same. In some cases they consist of gases , as in 
 the burning of Charcoal and Sulphur, &c. ; in 
 others, liquids are produced, as by the combustion 
 of oxygen and hydrogen gases, the product in that 
 case being merely water ; while in others, again, a 
 solid product is the result, — as when phosphorus is 
 burnt a white solid, called “ phosphorous acid,” being 
 then formed : and so with zinc, the combustion of 
 which produces a solid white rust, or oxide. 
 
 “ Now, if the heat evolved during combustion,” 
 thought Humphry, “proceeds from the liberation 
 of the latent caloric, or that which previously 
 existed in the substances in an insensible state, it 
 would follow that such heat should be given off 
 only when the combustibles pass from a rarer to a 
 denser form ; as, for instance, when water is pro- 
 duced by the burning of its two constituent gases, 
 or when the oxygen of the atmosphere becomes 
 fixed in some solid product, as in the oxides of zinc 
 or mercury. 
 
 “ But by combustion,” the boy went on, “ many 
 
 s 
 
253 
 
 THE WONDERS OF SCIENCE. 
 
 solid bodies are converted into gases ; and in such 
 cases, according to Lavoisier’s theory, instead of 
 heat being evolved, it should be absorbed, , and posi- 
 tive cold produced by the process of burning. 
 
 “ This, however, is not the case,” added Humphry. 
 “ The explosion of Gunpowder , for example, is 
 attended by immense heat, and yet the ingredients 
 composing it, in passing from the solid to the 
 gaseous state, expand some hundred-fold, having 
 their volume increased, it is said, no less than 250 
 times. So, again, the gas called Protoxide of 
 Chlorine , at the instant of decomposition evolves 
 light and heat with explosive violence, and yet it 
 is known to become one - fifth greater in volume 
 afterwards. The oily substance, too, called Chloride 
 of Nitrogen , on being made to enter into com- 
 bustion, is resolved into its elements with tremen- 
 dous force of inflammation, expanding into more 
 than 600 times its bulk : so that, according to 
 Lavoisier’s theory, a prodigious degree of cold 
 ought to be produced by such an expansion, whereas 
 light and heat are evolved by it.” 
 
 That the heat of combustion is due rather to 
 intense chemical action going on at such times* 
 Humphry made many experiments to prove. 
 
 First, he generated some Chlorine , or green gas.* 
 
 * Chlorine gas was called u oxy -muriatic acid ' 1 when Davy 
 was a boy, from being supposed to be a compound of oxygen and 
 muriatic acid gas . Davy, however, afterwards proved that this 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 259 
 
 This he did by mixing in a retort some common salt 
 with a little black oxide manganese, and some sul- 
 phuric acid and water. The gas which came over 
 was of a greenish -yellow colour, and had a pun- 
 gent, disagreeable smell, exciting cough and great 
 irritation in the lungs when inhaled. Having col- 
 lected some of this gas over warm water in a 
 receiver, with a stop-cock at the: op, the boy took 
 a retort which had another stop-cock fitted to the 
 end of it, and having introduced into this some 
 copper-leaf, he screwed the retort on to the plate 
 of his air-pump, and proceeded to exhaust it of air 
 as perfectly as he could. This done, he screwed 
 the stop-cock of the retort on to that of the receiver 
 in which he had collected the gas ; then, turning 
 on both cocks, the chlorine rushed up into the 
 retort, and the metal immediately became spon- 
 taneously ignited by it, and burnt in the gas with 
 considerable energy. 
 
 The experiment was then repeated with a little 
 powdered antimony, and the same vivid combus- 
 tion ensued. 
 
 Now these Humphry knew to be cases of mere 
 chemical affinity. The chlorine gas had a strong 
 tendency to combine with the metals employed, 
 and as these were used in the best form for pro- 
 
 same oxy-muriatic acid contained no oxygen whatever, and was 
 rather an elementary substance, being incapable of being resolved 
 into any two other bodies. 
 
260 
 
 THE WONDERS OF SCIENCE. 
 
 moting the combination, the union of the gas with 
 the copper and antimony was so rapid and ener- 
 getic, that combustion was the consequence.* 
 
 Next, the lad took some Sulphur , and in this he 
 heated some shavings of iron in a close vessel, 
 when the metal, in a short time, was seen to be- 
 come intensely ignited, and to burn, as it were, in 
 the vapour of the sulphur. This was most curious, 
 for sulphur he had never thought to be a supporter 
 of combustion. 
 
 Further, Humphry heated some platinum and 
 tin -foil, and at the moment when the two metals 
 fused into one mass they became, to his astonish- 
 ment, vividly ignited. 
 
 Nor was this all : the boy slacked some recently - 
 burnt lime in a dark place, and found that, when 
 the water was thrown upon it, the heat rose to 
 upwards of 500°, while a faint light was emitted. 
 
 Another substance, discovered since the date of 
 the above experiments, affords a striking illustra- 
 tion of the heat produced by energetic chemical 
 action. This is a peculiar liquid called Peroxide 
 of Hydrogen , (see p. 244,) consisting merely of water 
 combined with an extra quantity of oxygen. So 
 readily decomposible is this fluid, that at the heat of 
 boiling water evolutions of gas are produced with 
 
 * A piece of blotting-paper dipped in oil of turpentine , and ~ 
 introduced into a jar of chlorine gas , immediately becomes in- 
 flamed. 
 
THE WONDERFUL EFFECTS OF HEAT. 
 
 2G1 
 
 such violence as to cause an explosion ; and almost 
 all the metals, when in a state of minute division, 
 resolve it rapidly into its elements. The per- 
 oxides of lead, mercury, gold, platinum, &c., act on 
 the liquid with surprising energy, the decomposi- 
 tion of it being complete and instantaneous upon 
 dropping those substances into the liquid ; for 
 oxygen gas is then given off with such force as to 
 produce a detonation, while the temperature be- 
 comes so intense that the glass tube in which the 
 experiment is conducted grows suddenly red hot. 
 
 Subsequently, Humphry amused himself by mix- 
 ing a little Chlorate of Potash , about the size of a 
 pea, with the same quantity of loaf sugar , having 
 previously reduced each to powder. Then he 
 placed the mixture on a piece of tile, and, dipping 
 a glass rod into a bottle of strong Oil of Vitriol , 
 let the acid drop from the rod upon the powdered 
 Chlorate and sugar, when they were instantly kin- 
 dled, and burnt with a red and blue flame. For 
 the Vitriol immediately decomposed the Chlorate 
 of Potash, and so produced heat enough to ignite 
 the materials ; while the oxygen given out from 
 the Chlorate maintained the sugar in a state of 
 vivid combustion. A little Camphor , mixed with 
 Chlorate of Potash , and touched with a drop of 
 Oil of Vitriol , may be made to inflame in the same 
 manner. A like effect is also produced when the 
 Chlorate is mixed with Spirits of Wine . 
 
262 
 
 THE WONDERS OF SCIENCE. 
 
 After this, the lad placed a small piece of 
 Phosphorus , and a few grains of Chlorate of 
 Potash , at the bottom of a thin glass vessel, and 
 then poured gently upon them some hot water. 
 The heat of the water was sufficient to inflame 
 the Phosphorus, while the oxygen evolved from 
 the Chlorate of Potash in connexion with it tended 
 to keep up the combustion ; so that the two burnt 
 with a vivid and pleasing light under the water. 
 
 Now Humphry knew that the reason of these 
 effects was, that the Chlorate of Potash contains 
 a large quantity of oxygen, which, having a strong 
 tendency to combine with the combustibles, enters 
 rapidly and energetically into union with them im- 
 mediately their temperatures are elevated, and so 
 gives rise to the phenomena of heat and light, 
 which are evolved during the combustion. 
 
 The same result is produced by Nitre in ordi- 
 nary gunpowder, for this also contains a large 
 quantity of oxygen gas, which serves to inflame 
 the small particles of charcoal that are mixed with 
 it, while the sulphur — which forms the other ingre- 
 dient, — being inflammable at a low temperature, 
 renders the gunpowder capable of being united by 
 a mere spark. 
 
 Oxygen thus appeared to Humphry to be the 
 main “supporter of combustion,” while the body 
 burnt seemed to be the “ combustible.” 
 
 But Humphry had seen that bodies burnt in 
 
THE WONDERFUL EFFECTS OF HEAT, 
 
 263 
 
 Chlorine gas as well as in oxygen : this, therefore, 
 was another “ supporter of combustion.” The same 
 effect, again, he had found to be produced in the 
 vapour of sulphur. Sulphur, however, was a “ com- 
 bustible body so that, in this instance, the same 
 substance was both a combustible and a supporter 
 of combustion. 
 
 The division of all bodies, therefore, into these 
 two classes, as propounded by the French chemists, 
 appeared to have no foundation in nature. 
 
 Nevertheless, Humphry was determined to put 
 the matter to the test of experiment, and to see 
 whether the light and heat evolved during com- 
 bustion proceeded from the combustible itself, or 
 from the combination of it with the air during the 
 burning. 
 
 Accordingly, the lad inflamed a jet of hydrogen 
 gas in a vessel of oxygen, when the light and heat 
 certainly appeared to proceed from the jet of hy- 
 drogen , while the oxygen seemed to act merely as 
 the supporter of the combustion. 
 
 On reversing the experiment, however, and 
 causing the oxygen gas to issue from the jet, Hum- 
 phry found that he could inflame it in a vessel of 
 hydrogen, and that then the light and heat seemed 
 to be evolved from the burning oxygen , , while the 
 hydrogen appeared only to keep it inflamed. 
 
 It was evident, therefore, from the last experi- 
 ment, that even oxygen itself might be ranked. 
 
264 
 
 THE WONDERS OF SCIENCE. 
 
 among the combustibles , and hydrogen be con- 
 sidered as a supporter of combustion ; but Hum- 
 phry now saw that the real truth of the matter was, 
 that the heat and light evolved during combustion 
 came from neither one substance nor the other , but 
 arose simply from the rapid and energetic chemical 
 union of the two : for even two metals, at the 
 moment of their union, evolve heat and light, as 
 shown in the experiment of the fusion of platinum 
 with tin-foil. 
 
 Combustion, therefore, is simply the consequence 
 of the rapid chemical action of one body upon an- 
 other ; and the reason why it is necessary to ele- 
 vate the temperatures of certain bodies before they 
 can be inflamed, is merely because heat promotes 
 the chemical action of substances upon each other. 
 
HUMPHRY AND HIS “ WONDERFUL LAMP. 265 
 
 CHAPTER XT. 
 
 HUMPHRY AND HIS “ WONDERFUL LAMP.” 
 
 Humphry found it impossible to quit the subject of 
 Combustion without some inquiry as to the nature 
 of flame. * 
 
 “ What,” said he to himself, “ are those brilliant 
 sheets of light that dart from burning substances ? 
 And why is it that certain bodies burn with the 
 evolution of flame, and that others are merely 
 capable of being rendered incandescent at the 
 highest heat ?” 
 
 Now the boy had before reflected upon the pro- 
 duction of heat by the slow combination of oxygen 
 with certain combustible substances, so he imme- 
 diately passed to the consideration of the production 
 of light by the same means. 
 
 He knew well that a stick of phosphorus always 
 appears luminous in the dark, and that lines of fire 
 can be written with it on a wall : the reason of this 
 being simply that the air combines with it slowly 
 
266 
 
 THE WONDERS OF SCIENCE. 
 
 at ordinary temperatures. Again, the lad was 
 aware that decayed wood emits a faint light, which 
 is visible by night, the light being due to the same 
 cause, viz. the slow combustion which is continu- 
 ally going on in it ; for chemists have discovered 
 that the rotting vegetable substance is constantly 
 absorbing oxygen from the atmosphere, and evolv- 
 ing carbonic acid gas — the same as if it were really 
 burning — though at a less rapid rate. Moreover, 
 the decay of many animal substances, Humphry 
 had read, is attended with like phenomena, — the 
 flesh of many fresh and saltwater fish becoming 
 luminous previous to putrefaction. 
 
 But, in all such cases, the light emitted is more 
 like a halo, or fefeble glow , than the character of 
 flame; or, rather, it seems as if the substance had 
 become incandescent in the cold , and acquired the 
 property of ignition at. ordinary temperatures, so 
 that it was capable of giving out light without 
 being sensibly heated.* 
 
 Humphry had noticed, too, that a green wax 
 taper, — the colour of which he knew to be pro- 
 
 * A few flowers have also the property of emitting light at 
 ordinary temperatures. Among these may be cited the tube- 
 rose , nasturtium , and marigold , which occasionally give out 
 flashes of light on a warm summer’s evening. This, probably, 
 arises from the combination of the oxygen of the atmosphere 
 with the vapour of the volatile oils upon which the perfumes of 
 flowers are known to depend. Again, other substances emit light 
 during the act of crystallization . This phenomenon is most dis- 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 267 
 
 duced by “ verdigris” (acetate of copper), — on 
 being lighted and blown out shortly afterwards, will 
 continue glowing in the wick, or burning without 
 flame, until the whole of the taper be consumed. 
 
 Now this, the boy was well aware, was another 
 case of combustion, going on at a temperature 
 below that of flame, though it was a state of con- 
 tinuous incandescence, requiring a higher heat for 
 its production than the phosphorescence of decay- 
 ing vegetable and animal matter. 
 
 Having thought the matter well over for some 
 little time, the boy -Chemist eventually con- 
 ceived that it might be possible, by some such 
 means, to produce a lamp which would burn con- 
 tinuously, and give light, without flame ; and this 
 he imagined might be found of great service in the 
 coal-mines, since the fire-damp was not explosible 
 at the highest red heat , and required positive flame 
 to cause it to enter into combustion. 
 
 In the case of the glowing wick of a green 
 taper, the youth saw that it was necessary for the 
 wick itself to be made red hot before the ignition 
 
 tinctly observed during the gradual deposit of arsenious acid, 
 when dissolved in hot hydrochloric acid (spirits of salts). In a 
 dark place each crystal, as it is formed, may be seen to emit a 
 spark of light ; and on shaking the flask, so many crystals are 
 sometimes suddenly produced, that vivid flashes become percep- 
 tible. The cause of this phenomenon is probably dependent on 
 the fixation of oxygen by the arsenic at the moment of preci- 
 pitation. 
 
268 
 
 THE WONDERS OF SCIENCE. 
 
 could be maintained ; and he concluded that it 
 was merely the incandescence of the wick which 
 caused the gases given off from the taper to com- 
 bine with the air, and so to keep it continually 
 red hot. It struck him, therefore, that if he were 
 to use some combustible liquid that was highly 
 vaporisable, like ether, and to suspend above this a 
 spiral coil of fine platinum wire, which had been 
 previously heated to redness, the same continuous 
 state of ignition might be made to go on, and that 
 in a much simpler manner. 
 
 Accordingly, Humphry procured a tall ale-glass, 
 and having poured into it a tea-spoonful of ether 
 he suspended within it a coil of plati- 
 num-wire, which had been made red 
 hot in the flame of a spirit-lamp. 
 
 The arrangement of the little appa- 
 ratus is represented in the annexed 
 engraving. 
 
 Immediately the red-hot coil was 
 placed in the vapour from the liquid, the excited 
 boy was overjoyed to see it glow with a bright red 
 heat. He stood watching it for a long time, and 
 was rejoiced to find that there was not the least 
 diminution of the incandescence till the whole of 
 the liquid had disappeared, and the vapour been 
 made by the heat of the wire to combine with the 
 surrounding air. 
 
 Still it struck Humphry that a more convenient 
 
Humphry’s first attempt at the safety lamp. 
 
 Vatje 209 - 
 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 269 
 
 mode of attaining the same end might be devised ; 
 so he took an ordinary spirit-lamp (for spirits of 
 wine he was aware had the same tendency to give 
 off vapour as the liquid he had previously em- 
 ployed), and wound a coil of 
 fine platinum wire round the 
 wiclC — thus. Then, having 
 lighted the lamp, he suffered it 
 to burn for a few seconds, after 
 which he put an extinguisher 
 over the flame, and instantane- 
 ously removed it. The conse- 
 quence was, that the coil retained heat enough to 
 carry on the slow combustion of the vapour from 
 the spirit, so that the ignition was kept up, and 
 the wire continued glowing, till the whole of the 
 spirit had evaporated from the lamp. 
 
 Overjoyed at the discovery he had made, Hum- 
 phry hastened to exhibit his lamp without a flame 
 to Mr. Borlase and Mrs. Foxell, and his old friend 
 Mr. Tonkin : and as he did so, the boy descanted 
 fervently upon the superiority of such a means of 
 obtaining light in coal-mines over the “ steel-mills ” 
 which were then used for the purpose. 
 
 Mrs. Foxell was as pleased as the boy himself at 
 what she considered the successful termination of 
 his labours ; and when Humphry ran over to her 
 the long train of investigation he had pursued in 
 order to arrive at the object, she was warm in her 
 
270 
 
 THE WONDERS OF SCIENCE. 
 
 praises of his perseverance and genius, and assured 
 him that, by such patient inquiry, he must ulti- 
 mately gain the honours and the universal esteem 
 which he so much desired. 
 
 Mr. Borlase was surprised at the talent of his 
 young pupil, and went with him to Mr. Tonkin to 
 talk over the matter ; and when Humphry’s foster- 
 father saw what he had achieved, and was in- 
 formed of the benevolent spirit which had stirred 
 him to the discovery, the old gentleman hugged the 
 lad to him, and told him he was well repaid for all 
 the care and affection he had bestowed upon him. 
 
 When, however, the ffrst impressions had sub- 
 sided, and Humphry’s exultation at the discovery 
 he had made had been toned down by continually 
 reflecting upon the subject, he began to think his 
 little safety -lamp might be much improved if he 
 could only increase the light from it. In its pre- 
 sent form he thought it would be available merely 
 in such cases as the steel-mill was used, viz. to ex- 
 plore those mines which were known to be charged 
 with fire-damp. The miners, nevertheless, needed 
 some light at their work, and if candles or lanterns 
 were employed, the flame would be sure to ignite 
 any fire - damp that might accidentally become 
 mixed with the atmosphere, and so to cause the 
 whole to explode. 
 
 What was required, therefore, was a light which 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 271 
 
 would be as bright as those the miners employed 
 at their work, but which would, at the same time, 
 be incapable of inflaming the explosive gases evolved 
 from the coals. 
 
 Such a light Humphry knew could be obtained 
 only from flame itself, for he was now satisfied that 
 it was impossible for any one to see to work by the 
 rays from a red-hot wire. Still the difficulty was, 
 that the presence of flame would be sure to cause 
 the fire-damp to explode whenever it became mixed 
 with the air in the mines, and it was impossible to 
 make a lamp burn without air. 
 
 For a time the difficulties involved in the con- 
 struction of such a lamp appeared to the lad to 
 be insurmountable. At length, however, nothing 
 daunted, he set to work to discover the nature of 
 flame itself, and so to find out what conditions 
 were necessary for the production and maintenance 
 of it 
 
 “ Flame” said Humphry, while reflecting upon 
 the subject, “ may be regarded merely as a sheet , 
 or film , of gas , in a high state of ignition . The 
 temperature of flame is always very intense, since 
 it will ignite substances that cannot be lighted, 
 even with the highest heat of incandescence. The 
 light , however, emitted by different flames is by no 
 means equally vivid, since there are gases which 
 burn with the production of a flame so feeble as to 
 be scarcely visible in broad daylight.” 
 
272 
 
 THE WONDERS OF SCIENCE. 
 
 Accordingly it struck the boy, that the best way 
 to proceed would be to produce a feeble light first, * 
 and then to ascertain by what means he could in- 
 crease the brilliance of it. So Humphry made a 
 large bladder full of hydrogen gas, and then an- 
 other bladder of oxygen, and proceeded to burn the 
 gases together by means of two blow-pipes. 
 
 The flame produced was of a very faint blue 
 colour, and though the boy closed the shutters, he 
 could barely see to read by the light, and yet the 
 heat of it was almost as intense as any that could 
 be artificially generated ; * for, on holding a pla- 
 tinum wire in the flame, it immediately became 
 white hot, and the light was considerably aug- 
 mented. 
 
 “ So, then,” cried Humphry, “ the light emitted 
 by a flame seems to be increased by solid sub- 
 stances introduced into it, and ignited by it.” 
 
 This set the boy wondering what would be the 
 effect if he were to cause some fine dust to pass 
 continually through the flame, and whether the 
 brigh tness of the light would be as much increased 
 then as it was when the platinum wire was intro- 
 duced into it. 
 
 The idea had no sooner struck him than he ran 
 down to the shop, and procuring a little magnesia 
 
 * The blue colour of the oxy-hydrogen flame is due, probably, 
 to the particles of water formed by the combustion of the two 
 gases. 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 273 
 
 in fine powder, proceeded to sift this into the flame 
 produced by the oxygen and hydrogen gases. 
 
 The result was almost magical. 
 
 No sooner did the fine white particles fall into 
 the flame, than the light was changed from a faint 
 blue into a brilliant white; while the little solid 
 specks shone like so many gem-points in the sun- 
 shine, producing a glare that it pained the eyes to 
 look at, and that instantly lighted up the little dark 
 chamber almost with the vividness of daylight. 
 
 “It is as I expected !” shouted Humphry, as he 
 gazed with admiration at the beautiful white light ; 
 “ the luminosity of a flame depends chiefly upon 
 the particles of solid matter diffused through it, and 
 rendered incandescent by the burning gases. The 
 flame of a candle or oil-lamp,” the boy continued, 
 “owes its brightness merely to the same cause ; for 
 there the oil, or grease, is converted into gas by the 
 heat of the wick, and this gas consists chiefly of 
 carburetted hydrogen, — that is to say, of charcoal 
 and hydrogen combined together : so that in burn- 
 ing, the hydrogen unites with the oxygen of the 
 air and forms water, while the charcoal is set free, 
 and passes up through the flame in the form of 
 very minute particles, which being burnt there, and 
 so rendered nearly white hot, cause the light to 
 shine with great vividness.” 
 
 To prove that the light of an ordinary candle, or 
 oil-lamp, is due merely to the brilliancy of the in- 
 
 T 
 
274 
 
 THE WONDERS OF SCIENCE. 
 
 candescent particles of charcoal continually passing 
 through the flame, the lad was not satisfied merely 
 with holding a burning candle against the ceiling, 
 and so causing the unburnt charcoal to be deposited 
 upon it in the form of “ lamp-black,” as it is called ; 
 but he passed some hydrogen gas through a small 
 reservoir of naphtha, and found that the brilliancy 
 of the light was greatly increased by it : for, the 
 naphtha being merely a liquid form of charcoal and 
 hydrogen in combination, the gas, on traversing 
 the fluid, took up a certain portion of the naphtha 
 in vapour, and this being very rich in charcoal, 
 was the cause of the increased illuminating power 
 given to the flame. 
 
 The same principle has been applied since Hum- 
 phry’s time to the production of some of the most 
 vivid of our artificial lights. The “ Drummond 
 light,” for instance — which consists merely of a 
 jet of oxygen and hydrogen gases projected against 
 a cylinder of lime — owes its intense brilliancy 
 solely to the particles of lime that are rendered 
 white hot by the flame of the burning gases ; and 
 that the lime passes off in vapour is proved by the 
 fact, that, during the combustion, the roof of the 
 lantern becomes covered with the sublimed par- 
 ticles. 
 
 Again, the brilliancy of the electric light itself 
 is known to arise from the particles of white-hot 
 charcoal that pass over in vapour from one pole 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 275 
 
 of the battery to the other ; for it is found that 
 the charcoal point in connexion with the positive 
 pole becomes decreased and burnt into a cavity, 
 while that in connexion with the negative pole is 
 proportionately increased, having a small knob 
 or protuberance of charcoal deposited upon it: 
 so that, strange as it may appear, the brilliancy 
 of the flame of a common tallow-candle depends 
 upon the same cause as that of the electric light 
 itself. In the one case, however, the combustion 
 being imperfect, the points of charcoal are less 
 vividly ignited ; whereas in the other, the heat 
 being the most intense that can be produced by 
 artificial means, the incandescence is proportion- 
 ately higher, and the brilliancy of the light, there- 
 fore, increased to the greatest point. In a word, 
 the particles of charcoal in the flame of a candle 
 are only at an orange heat, whereas those in the 
 voltaic flame are at the highest white heat that art 
 can generate. 
 
 Accordingly, artificial light would appear to be 
 due solely to artificial heat , and the illuminating 
 power of even flame itself to depend upon the in- 
 candescence of the particles of solid matter diffused 
 through the burning gases. 
 
 Humphry’s next object was to discover whether 
 flame really consisted, as he before said, of a sheet 
 or film of gas in a state of combustion. 
 
270 
 
 THE WONDERS OF SCIENCE. 
 
 “ The flame of a common candle,” he mused, 
 “ appears to be a solid cone of luminous matter. 
 Is it, however, really alight in the middle ?” the 
 boy mentally inquired; “ or is it burning at the out- 
 side only, so that the thin film of white-hot vapour 
 incloses a portion of combustible matter within it, 
 which cannot burn for want of air ? How can I 
 ascertain this ?” 
 
 Humphry thought for a while, and then it struck 
 him, that if he were to place a piece of thin glass 
 upon the flame itself, so as to press it down as it 
 were, he could then see whether or not it were 
 alight in the middle ; for if it were alight round 
 the edge only, he would behold through the glass a 
 bright ring of flame, with a dark spot in the centre, 
 indicating the portion where the combustion was 
 not going on. 
 
 The experiment was soon tried, and the result 
 proved as Humphry had anticipated. A luminous 
 circle was seen through the glass, at the point 
 where the flame touched the surface, and in the 
 centre of this there was a dark 
 spot, like a black wafer, show- 
 ing where the decomposed char- 
 coal gas existed in the interior 
 of the flame in an unburnt state. 
 The appearance, however, is re- 
 presented in the subjoined illus- 
 tration. Indeed Humphry perceived, that as air was 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 277 
 
 necessary for combustion, and it was impossible 
 for the atmosphere to get to the interior of the 
 flame, the outside only of the cone of combustible 
 gases, evolved from the decomposed tallow, could 
 be alight ; while the vapour in the centre could 
 be burnt merely as it passed off into the air at 
 the upper part of the flame. 
 
 The next step was to see whether the interior 
 dark part of the flame really consisted of the same 
 inflammable gases as were in a state of combustion 
 at the exterior, or surface of it. 
 
 Accordingly, Humphry placed a small glass tube 
 within the centre of the flame 
 from an ordinary candle, and found 
 that the unburnt gas from the in- 
 terior readily made its way up 
 the tube, and escaped at the top 
 of it, and that on applying a light 
 to this it was immediately ignited ; 
 so that two flames were thus pro- 
 duced from one candle, as here 
 shown. 
 
 Another proof that the gases in the interior of 
 the flame were not in a state of combustion was 
 afforded by lighting some spirits of wine in a large 
 spoon ; for Humphry then found that he could 
 introduce some grains of gunpowder, and even 
 some pieces of phosphorus, by means of a tube, 
 
273 
 
 THE WONDERS OF SCIENCE. 
 
 into the middle of the flame, without igniting 
 them. 
 
 Humphry, moreover, could now see that the 
 reason why the blow-pipe so much increased the 
 heat of an ordinary flame is simply because a cur- 
 rent of air is made by such means to traverse the 
 interior part of it, so that the combustion being 
 rendered more perfect, the temperature, of course, 
 becomes proportionately higher. 
 
 Again, the wick of the “ Argand Lamp ” is 
 constructed circular, so that a current of air may 
 be supplied to the interior of the flame ; and hence 
 the superior brilliancy of this kind of burner. 
 Table-lamps are now generally made upon the same 
 principle, and so, indeed, are the gas-burners in 
 shops. Sometimes, however, a jet is used, with 
 the holes so arranged as to spread the gas into a 
 thin wide sheet, and thus allow the air to act upon 
 a large surface of combustible matter at each side. 
 These are called “ bafs wing ” and “ fish-tail 99 
 burners, &c., according to the shape of the flat 
 broad flames produced by them. 
 
 The next point in the inquiry was to discover 
 what would be the effect of cooling down a flame, 
 since it was evident that it required a very high 
 temperature for its existence . 
 
 Humphry was well aware that, by projecting a 
 current of cold air upon substances in a state of 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 279 
 
 combustion, the flames were generally extinguished. 
 Still he wished to see whether it was not possible 
 to lower the temperature of a flame by some other 
 means. 
 
 Accordingly he procured a piece of wax-candle, 
 and proceeded to pull out all the wick, except one 
 thread, so that when it was lighted the flame from 
 it should be as small as possible. Then the boy 
 made a little ring of iron wire, about the eighth of 
 an inch in diameter, and this he affixed to a wooden 
 handle. Passing the wire ring over the lighted 
 wick he found, that on bringing it a little below 
 the flame the light was immediately extinguished, 
 for the metal, being a good conductor of caloric, 
 served to carry off the heat which was necessary 
 for the maintenance of the flame. 
 
 It then struck Humphry that the pins which 
 housewives stuck in rushlights- that they wished to 
 be extinguished at a certain time, acted merely upon 
 the same principle — the metal carrying off the 
 heat, and so lowering the temperature requisite for 
 the existence of the light. 
 
 The youth thought for a long time as to whether 
 he could avail himself of this principle in any way 
 for the construction of his safety -lamp, for, as he 
 had now discovered that it was possible to extin- 
 guish flame merely by reducing its temperature — 
 and that a piece of wire, placed in connexion with 
 it, did this most effectually — he fancied he might 
 
280 
 
 THE WONDERS OF SCIENCE. 
 
 take advantage of some such means for preventing 
 the passage of flame to fire-damp. But though 
 he racked his brain long he could hit upon no plan 
 for accomplishing his object. So he contented 
 himself with merely making a memorandum of the 
 fact in his note-book, saying to himself, that he 
 knew it would prove serviceable some day — and 
 then passed on to another part of his inquiry. 
 
 Fire-damp, he was well aware, is explosible 
 only when mixed with the atmosphere ; for the air 
 is necessary for the combustion of all substances, 
 and explosion, as before observed, is merely the 
 result of instantaneous combustion . Still, certain 
 liquids, Humphry knew, are attracted by the sides 
 of fine tubes, so that the fluid in which they are 
 immersed is maintained within them above the 
 level of that without. He knew, too, that by the 
 same principle a certain quantity of water might 
 be retained in a fine sieve without running through 
 the holes ; and that a vessel full of small holes 
 might, for the like reason, be immersed to a cer- 
 tain depth in water without sinking, or any of 
 the liquid entering it. 
 
 So the lad was anxious to see what would be the 
 effect of fine tubes upon gases, and whether, upon 
 passing an explosive mixture of carburetted hy- 
 drogen and air along a narrow glass pipe, the flame 
 would pass down it, or be arrested in its progress. 
 
 Accordingly, having prepared some carburetted 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 281 
 
 hydrogen gas, and mixed it with eight parts of 
 air — for these proportions he had found to be the 
 most explosive — he passed the mixture along a 
 glass tube, the bore of which was only -1 of an inch 
 in diameter, and discovered, on lighting the gas 
 that issued from the end of it, that the flame, in- 
 stead of travelling down the narrow channel, and 
 being instantly communicated to the whole of the 
 explosive mixture, remained stationary at the orifice 
 of the tube, where the gases burnt as slowly and 
 quietly as with an ordinary candle. 
 
 Humphry was half-bewildered with joy at the 
 discovery he had made. Fire-damp he had now 
 ascertained was not explosible within narrow tubes, 
 and instantly a hundred and one plans flashed across 
 his mind for rendering the fact serviceable to those 
 engaged in the coal-mines. 
 
 Still there was much to work out. It was ne- 
 cessary to know through how large a tube flame was 
 capable of being transmitted ; so he procured an- 
 other glass pipe, the bore of which was a quarter 
 of an inch in diameter, or double that of the one 
 he had first employed, and passing the same ex- 
 plosive mixture along it, he found that, on lighting 
 the gases at the end of this, the flame no longer 
 remained stationary at the orifice, but travelled 
 slowly down the channel, taking more than a second 
 before it reached the other end, though the tube 
 itself was only a foot long. 
 
2S2 
 
 THE WONDERS OF SCIENCE. 
 
 Then pursuing the same course of experiments, 
 Humphry subsequently discovered that by dimi- 
 nishing the diameter of the tube he could shorten 
 the length of it without any danger of the flame 
 travelling along it, and so causing the gases without 
 to explode. Moreover, the lad ascertained that when 
 fine metal tubes were substituted for glass ones, the 
 security was even more perfect. 
 
 To insure greater safety, however, by making 
 the channel through which the explosive gases 
 passed as fine as possible, he ultimately inserted 
 some short pieces of metal tubing, one within the 
 other; so that the bores being 
 of different diameters, they 
 formed a series of broad 
 concentric rings, each en- 
 closing another, and having 
 a fine channel between them 
 — thus. 
 
 These Humphry proved 
 to be perfectly secure against all explosion, and 
 then proceeded to fix one set at the bottom of a 
 lamp, and another at the top of a glass chimney 
 that was made to fit air-tight round the flame. 
 The concentric tubes at the bottom were for the 
 supply of air to the light, and those at the top for 
 the issue of the smoke ; so that thus, if any fire- 
 damp were present in the mine, and entered with 
 the atmosphere through the air-tubes at the bottom, 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 283 
 
 the flame would not be communicated to the ex- 
 plosive gases outside the lamp, — and thus the safety 
 of the miner would be thoroughly ensured. 
 
 For rendering the arrangement adopted more 
 intelligible, a design of Davy’s first Safety-Lamp 
 is here given. 
 
 The principle upon which this 
 lamp depended for its security 
 had been so carefully worked out 
 that it scarcely required testing. 
 
 To assure himself, however, of 
 its efficacy, the boy immersed the 
 lamp in the most explosive mix- 
 ture of carburetted hydrogen and 
 air that he could possibly form, 
 and was well repaid for all his 
 labours by seeing that the flame 
 was incapable of being trans- 
 mitted to the combustible gases 
 without ; so that, upon their entering the lamp, 
 the light itself was extinguished. In a word, he 
 found that his lamp was “ absolutely safe,” and 
 that the fire-damp had been disarmed by him of 
 its terrors. 
 
 Humphry’s friends were as delighted as the boy 
 himself at the successful termination of his labours. 
 Mrs. Foxell, who had, in the first instance, en- 
 couraged him to proceed, was, perhaps, the most 
 gratified of all ; nor did she refrain from lecturing 
 
284 
 
 THE WONDERS OF SCIENCE. 
 
 her brother, Mr. Borlase, upon his previous want 
 of faith in the accomplishment of the result, telling 
 him that it was cruel, where so many lives were at 
 stake, to damp the ardour of any one who could 
 believe in the possibility of rendering them secure 
 for the future. 
 
 Mr. Borlase was sufficiently generous to confess 
 his error, and frankly acknowledged that he never 
 thought Humphry would be able to accomplish half 
 as much as he had. 
 
 The boy’s old friend, Mr. Tonkin, too, felt prouder 
 than ever of his foster-son, when he saw the lad 
 test the powers of the lamp in his presence; and 
 the old gentleman made Humphry’s heart swell 
 again with the praises he heaped upon him, and 
 the tears start to his eyes with the confession of 
 the long love he had borne the boy. 
 
 At length, however, Mr. Tonkin said that he 
 thought one improvement still was required, though 
 how it was to be effected he must leave Humphry to 
 find out, for it was more than he could manage. 
 On the admission of the fire-damp into the lamp 
 the light was extinguished. “ This,” the old gentle- 
 man observed, “ appeared to be a great defect, for 
 the extinction of the flame was a sure indication 
 that danger surrounded those who carried the lamp ; 
 and to leave the miner in darkness at a time when 
 immediate flight was necessary, struck him as being 
 a serious drawback to its utility. If Humphry, 
 
HUMPHRY AND HIS " WONDERFUL LAMP.” 2S5 
 
 therefore,” he said, “ could, by some means or other, 
 arrange it so that the light should continue burning, 
 even in the presence of the fire-damp itself, the in- 
 genuity of the apparatus would not only be much 
 greater, but its value be considerably enhanced.” 
 
 Humphry saw the force of Mr. Tonkin’s objec- 
 tion, and it struck him that the defect was almost 
 irremediable. He was, therefore, not a little vexed 
 to find that an instrument which he had fancied 
 perfect, was not altogether faultless. 
 
 The lad pondered over the matter for many days, 
 and tried a number of experiments to overcome the 
 difficulty which had been raised. It proved, how- 
 ever, beyond his powers ; so, exhausted by his long 
 study, and vexed at the idea of his comparative 
 failure, Humphry, at length, dismissed the subject 
 from his mind, and locked the safety -lamp in his 
 cupboard, determined that it never should be made 
 public until it was perfect in all its arrangements. 
 
 It was in vain that Mrs. Foxell urged him to 
 make known the invention, even in an unfinished 
 state : but the boy was firm in his resolve. 
 “ Some day” said he, “ it shall be completed, and 
 then the world may have it, and welcome ; but 
 as it is now, it is hardly worth either the giving 
 or accepting, and no honours can come of it. 
 When I know more,” he added, “ I can do better : 
 nor do I intend, because I have been baffled in 
 this my first project, to give over studying ; for I 
 
286 
 
 THE WONDERS OF SCIENCE. 
 
 find such delight in the perception of the new 
 truths which are daily unfolded to me, that I would 
 rather forego any source of pleasure than that 
 which comes from scientific discovery.” 
 
 It was many years before the Safety-Lamp was 
 perfected; and when it was, the alteration was 
 so slight, that it has been well observed, — “The 
 history of this elaborate inquiry affords a striking 
 proof of the inability of the human mind to appre- 
 hend simplicities without a long process of pre- 
 vious complication.”* 
 
 Humphry Davy, as we have narrated, had 
 already discovered, while experimenting upon the 
 inflaming of explosive gases in narrow tubes, that, 
 provided he diminished the bore, he could shorten 
 the length of them in a corresponding ratio. Now 
 a sheet of wire-gauze, it is obvious, consists merely 
 of a series of fine tubes, of very short lengths. It 
 appears strange, therefore, that our hero was some 
 time before he conceived the happy idea of con- 
 structing his lamp entirely of wire-gauze, instead 
 of feeding it with air through narrow channels, or 
 “safety canals,” as he called them; for, as flame 
 cannot be transmitted along small tubes, it is mani- 
 fest that, on surrounding a lamp with a wire-gauze 
 cylinder, or cage, the fire-damp, as it enters with 
 the air, will burn within the cage itself, and the 
 * Dr. Paris’s “ Life of Sir Humphry Davy,” p. 352. 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 287 
 
 flame be incapable of passing through the small 
 apertures in the gauze, and thus exploding the gas 
 outside of it. 
 
 To render the action of wire -gauze in this re- 
 spect more intelligible, a few of Humphry Davy’s 
 after-experiments may be cited in connexion with 
 this part of the subject. 
 
 If a small piece of wire-gauze (say about 9 
 inches square, and having about 30 meshes to the 
 square inch) be gradually brought down upon the 
 flame of a candle, the flame itself will be cut off 
 where it touches the gauze, and merely a dark spot 
 be there observed, encircled by a ring of light, 
 while the combustible matter of the flame will issue 
 through the small apertures in the form of smoke ; 
 for during the passage of the burning gases through 
 the metallic meshes they will be so far cooled down 
 that the flame will be extinguished, and thus ren- 
 dered incapable of traversing the gauze itself. 
 
 If, however, a lighted taper be held above the 
 wire-gauze, the inflammable gas or smoke from the 
 candle will be immediately rekindled, and the flame 
 continue to burn then, both on the upper and under 
 side of the tissue. 
 
 But the impermeability of metallic gauze to 
 flame may be rendered still more evident, by placing 
 a piece of fine wire web above a jet of gas pre- 
 vious to lighting it, when it will be found that, if 
 a burning taper be held over the wire web, the gas 
 
233 
 
 THE WONDERS OF SCIENCE. 
 
 will be kindled above it, and continue to burn upon 
 the gauze itself, while the com- 
 bustible matter beneath will re- 
 main unignited ; for the metallic 
 threads, being good conductors of 
 heat, will so cool the flame as 
 to prevent it passing through to 
 the gas on the lower side. 
 Again, if a small piece of cam- 
 phor be laid in the centre of a sheet of wire-gauze, 
 and a light held beneath it, the vapour from the 
 camphor, which is very inflammable, 
 will be made to burn with a bright 
 flame downwards — instead of up- 
 wards, as flames usually do — while 
 the camphor itself will lie upon the upper side of 
 the tissue in an uninflamed state. 
 
 The power of metallic webbing thus to inter- 
 cept or extinguish flame, depends simply upon the 
 cooling effect it produces ; so that as flame requires 
 a high temperature for its existence, it is plain 
 that it no sooner becomes cooled, by being passed 
 through a good conductor of heat, than it is ex- 
 tinguished. 
 
 If, however, the meshes of the wire-gauze be 
 not sufficiently small, or if the wire of the gauze 
 itself becomes intensely heated, the flame will tra- 
 verse it in either instance ; because the cooling 
 power is reduced, in the one case, by the largeness 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 289 
 
 of the apertures, and in the other by the high 
 temperature of the wire. 
 
 For the knowledge of these facts, we repeat, we 
 are indebted to the after-investigations of Davy 
 himself. 
 
 Now it is evident from the above experiments, 
 that if a lamp be covered with a cylindrical cage 
 of wire-gauze, no flame will be able to pass from 
 the interior of the lamp to the exterior of it, in 
 consequence of the cooling power of the metallic web 
 encompassing it ; so that, if the surrounding air be 
 charged with an explosive gas, it will enter the lamp 
 through the meshes of the web and burn within the 
 cage, while that without will remain unkindled. 
 
 Such, then, is the principle of the “ Safe-Lamp ” 
 as perfected by Davy, and which is here shown : — 
 
290 
 
 THE WONDERS OF SCIENCE. 
 
 The safety of this lamp may be exhibited by 
 immersing it in a large jar, at the bottom of which 
 is a little Ether ; for the vapour from this liquid, 
 on mingling with the air, forms a highly inflam- 
 mable atmosphere. On introducing the lamp into 
 this, the flame first becomes enlarged and is then 
 extinguished, while the whole of the cage remains 
 filled with a lambent blue light. On withdrawing 
 the lamp, however, and bringing it into the open 
 air, the wick is suddenly rekindled, and the flame 
 returns to its natural size and colour. 
 
 For perfect safety, it is necessary that the wire- 
 gauze of these lamps should contain about 30 
 wires, or 900 apertures in every square inch, and 
 that the heat of the wire itself should never rise 
 above redness ; for “ if,” as Davy said, “ the iron 
 wire become white hot, the lamp will be no longer 
 safe. This, however,” he adds, “ need never hap- 
 pen in a colliery $ for if a workman finds the tern-' 
 perature of the wire increasing rapidly in an ex- 
 plosive atmosphere, he can easily diminish the heat 
 by turning his back upon the current, and keeping 
 it from playing upon the gauze by means of his 
 clothes.” 
 
 Of this wonderful lamp it has been well said, 
 “ that it is a present from Philosophy to the Arts, 
 and to the class of men farthest removed from the 
 interests of science. We know of no discovery in 
 which the admirer of Science and the lover of 
 
HUMPHRY AND HIS “ WONDERFUL LAMP.” 291 
 
 mankind have greater reason to congratulate one 
 another. The discovery,” adds the late Professor 
 Playfair, “ is in no degree the effect of accident ; 
 and chance, which comes in for so large a share in 
 the credit of human inventions, has no claims on 
 this, which is altogether the result of patient and 
 enlightened research. The great use of an imme- 
 diate and constant appeal to experiment cannot be 
 better evinced than in this example. The result is 
 as wonderful as it is important. An invisible and 
 impalpable barrier, made effectual against a force 
 the most violent and irresistible in its operations, 
 and a power that, in its tremendous effects, seemed 
 to emulate the lightning and the earthquake, con- 
 fined within a narrow space, and shut up in a net 
 of the most slender texture ; these are facts which 
 must excite a degree of wonder and astonishment, 
 from which neither ignorance nor wisdom can de- 
 fend the beholder. When to this we add the bene- 
 ficial consequences, and the saving of the lives of 
 men, and consider that the effects are to remain 
 as long as coal continues to be dug from the bowels 
 of the earth, it may fairly be said that there is 
 hardly, in the whole compass of art or science, a 
 single invention of which one would rather wish 
 to be the author.”* 
 
 It should be borne in mind, moreover, that Davy 
 
 * “ Edinburgh Review,” January 1816. 
 
292 
 
 THE WONDERS OF SCIENCE. 
 
 in the accomplishment of his noble task, not only 
 did not seek, but positively rejected all pecuniary 
 reward ; so that it becomes difficult which to ad- 
 mire the most, — the benevolence which prompted 
 him to undertake the long train of laborious inves- 
 tigations, the genius which carried him to so 
 successful an issue, or the noble disinterestedness 
 which bade him refuse to traffic in an invention 
 that was destined to mitigate the sufferings of some 
 of the poorest and least-educated of his fellow- 
 creatures.* 
 
 * “ It will hereafter be scarcely credited,’ ’ says Dr. Paris, 
 “that an invention so eminently philosophic, and which could 
 never have been derived but from the sterling treasury of science, 
 should have been claimed in behalf of an enginewright of Kil- 
 lingworth colliery, of the name of Stephenson ; a person not 
 even professing a knowledge of the elements of chemistry. The 
 “enginewright” here sneered at for his ignorance, ultimately rose 
 to be the great George Stephenson, the inventor of the locomo- 
 tive. How would the fashionable physician speak of the quondam 
 enginewright of Killingworth colliery now ! Stephenson’s lamp 
 was formed on the principle of admitting the fire-damp by narrow 
 tubes, and “in such small detached portions, that it would be 
 consumed by combustion.” The two lamps were, doubtlessly, 
 distinct inventions, though Davy, in all justice, appears to be 
 entitled to precedence, — not only in point of date, but as regards 
 the long chain of inductive reasoning concerning the nature of 
 flame by which his result was arrived at. 
 
HUMPHRY PRACTISES ON HIMSELF. 
 
 m 
 
 CHAPTER XII. 
 
 HUMPHRY PRACTISES AS A SURGEON ON HIMSELF. 
 
 Humphry by this time desired some little recrea- 
 tion. He had been at work for many weeks un- 
 interruptedly — his days given to his profession, 
 and his leisure, in the evenings, devoted to the 
 prosecution of his scientific discoveries ; and what 
 with the exhaustion of continuous thought, and 
 the vexation at his inability to perfect the lamp, 
 from which he had such high hopes of honour, the 
 lad felt incompetent to resume his labours until 
 his mind, by diversion, had recovered somewhat 
 of its ordinary elasticity. 
 
 Accordingly, he determined upon enjoying a day 
 or two’s fishing with his uncle Millett — for this was 
 Humphry’s favourite pastime throughout life ; and 
 the sport, his biographer tells us, “ was alike his 
 relief in toil and his solace in sorrow.” * 
 
 * 11 Davy’s passion for angling betrayed itself upon all occa- 
 sions,” says Dr. Paris ; “ whenever I had the honour of dining 
 at his table, the conversation, however it might have commenced, 
 
294 
 
 THE WONDERS OF SCIENCE. 
 
 It was now spring, moreover, when the small 
 streams, the youth knew, were in the best state for 
 angling — turbid, in a slight degree, from the mild 
 rains common in April and May; so Humphry, 
 having arranged his tackle on the over-night, sal- 
 lied forth the next morning to join his uncle at 
 Marazion. 
 
 The lad’s fishing costume was singular enough 
 to claim some notice. It consisted of an entire suit 
 of green — that colour being considered by him the 
 most likely to elude the observation of the fish. 
 The coat was half covered with lappets of the 
 many pockets for holding the necessary tackle ; 
 and his hat (which was a round felt one, with a 
 broad brim like a wagoner’s), had been dyed of 
 the same colour as his clothes by a pigment of his 
 own composition ; while round the hemispherical 
 crown were coiled a series of fine lines, each ter- 
 
 invariably ended on fishing; and when a brother of the angle 
 happened to be present, you had the pleasure of hearing all 
 his encounters with the finny tribe — how he had lured them 
 by his treachery, and vanquished them by his perseverance. 
 He would occasionally strike into a most eloquent and im- 
 passioned strain upon some subject which warmed his fancy ; 
 such, for example, as the beauties of mountain scenery : but 
 before you could fully enjoy the prospect which his imagination 
 had pictured, down he carried you into some sparkling stream, 
 or rapid current, to flounder for the next half-hour with a hooked 
 salmon. . . . Nothing irritated him so much as to find 
 
 that his companions had caught more fish than himself, and if, 
 during conversation, a brother fisherman surpassed him in the 
 relation of his success, he betrayed similar impatience.” 
 
HUMPHRY EQUIPPED FOR 
 
HUMPHRY PRACTISES ON HIMSELF. 
 
 295 
 
 minating in some peculiarly-coloured artificial fly : 
 so that the hat appeared somewhat like a clod of‘ 
 turf upon which so many bees and moths had set- 
 tled. His legs, again, were encased in a huge pair 
 of jack-boots, which, for the convenience of wading 
 through the water, reached above his knees ; in- 
 deed, as Macbeth says of the witches, “ He looked 
 not like an inhabitant o’ the earth, and yet was 
 on’t”* 
 
 Thus equipped, Humphry, as we said, sallied 
 forth, with the joints of his rod strapped toge- 
 ther — like a small bundle of fagots — and resting 
 on his shoulder, while at his back projected 
 the wicker fish-basket, as if it were a huge car- 
 touche-box. Over the other shoulder were slung 
 the heavy jack-boots, and at his side ambled his 
 favourite water-spaniel “ Chloe,” her long tail 
 wagging as she stopped now and then to look up 
 in her master’s face, for she seemed to be as de- 
 lighted as the boy himself at the anticipation of the 
 sport that she knew was about to ensue. 
 
 The youth paused occasionally to fondle the 
 knowing creature, for he had had her since a pup — 
 having begged the gift of her when she was taken 
 from her mother, and about to be drowned with the 
 rest of the litter as soon as born, and it was only by 
 great care that he had been able to rear her, so 
 
 * See Dr. Paris’s description of Davy’s ordinary fishing cos- 
 tume, p. 189. 
 
296 
 
 THE WONDERS OF SCIENCE. 
 
 that the two were as attached to each other as any 
 human friends could be ; nor did Humphry treat 
 her as a dumb animal, but spoke to her as though 
 she understood every word he said : and, perhaps, 
 in his heart, the boy (with his half-poetic and half- 
 metaphysic theories) believed she did. * 
 
 It was late that evening before the couple re- 
 turned from the day’s sport, and then Chloe carried 
 in her mouth a small basket containing a portion of 
 the spoil, for Humphry’s wicker knapsack was not 
 capacious enough for the whole, as he and his 
 uncle Millett — so runs the record — had caught no 
 less than “ seven dozen trout in the rivulet and mill- 
 pond near the residence of the Rev. Mr. Giddy, in 
 the parish of St. Earth.” 
 
 Humphry’s success at his sport had made him 
 too light-hearted to feel the fatigues of the day, and 
 although he was somewhat foot-sore from the long 
 use of the heavy boots he now carried over his 
 shoulder, the boy and Chloe jogged merrily past the 
 tanneries at the extreme west of the town ; for the 
 dog knew as well as her master, by the leathery 
 
 * “ This favourite dog is well remembered in Penzance,” 
 says Davy’s brother. u My sister writes,” he adds, u that ‘ on 
 his first return from Bristol, after an absence of about twelve 
 months, Chloe did not remember him, till he called her by name, 
 and then she was in a transport of joy.’ Her descendants are 
 now numerous in the Mount’s Bay, and prized for good qua- 
 lities.” Yol. i. p. 54. 
 
HUMPHRY PRACTISES ON HIMSELF. 
 
 297 
 
 smell that filled the air at that quarter, that they 
 were not far from home then ; and Humphry, as 
 he patted the fond animal, promised her a good 
 supper of fish for all that she had done that day. 
 
 As they passed down Market -Jew Street the 
 oil-lamps and candles were being lighted in some 
 of the little shops, and Humphry saw, as he looked 
 towards the Town-Hall at the end of the street, 
 that the sun had long since set, for the sky was 
 grey with the thickening dusk, and the stars were 
 beginning to peep out of the haze, one after another, 
 through the darkening firmament. 
 
 At length the Town-Hall itself was reached, and 
 the youth was telling Chloe that she should soon 
 have her supper now, when suddenly a loud cry 
 was heard. As the lad turned round towards the 
 street that led to Madern Church to ascertain the 
 cause of the noise, he beheld to his horror a 
 huge dog, at full speed, hurrying in that direction, 
 white with foam at the mouth, and followed by a 
 mob of affrighted people, hooting and hallooing at 
 its heels. Some of the men were armed with 
 pikes, and others carried muskets, intent on the 
 destruction of the rabid animal. 
 
 Humphry, with Chloe still by his side, was within 
 a few paces of the furious creature. The boy saw 
 in an instant that flight was impossible, and dreading 
 lest his favourite dog should be attacked, he shouted 
 
298 
 
 THE WONDERS OF SCIENCE. 
 
 “ Back ! back ! ” to her in his most commanding 
 tone. The order, however, was too late, for Chloe, 
 being a little in advance of her master, had already 
 attracted the notice of the infuriated brute, and 
 Humphry saw her danger at a glance. In another 
 moment his own dog would be seized by the rabid 
 one, and the slightest graze from its teeth he knew 
 would be sufficient to render Chioe’s immediate de- 
 struction a matter of duty. It was no time for 
 reflection, so the excited boy, eager to save the life 
 of his favourite spaniel, rushed past her with his 
 heavy fishing-rod raised high in the air, and ready 
 to fell the dangerous brute to the earth. 
 
 Ere he could aim a blow, however, the hunted 
 dog had fastened on Humphry’s leg, and fixing his 
 fangs in the flesh, inflicted a wound that made the 
 lad shriek again with the suddenness of the pain. 
 
 The cry of her master brought Chloe instantly 
 to the rescue, and dropping her basket of fish she 
 sprang, yelping, towards the savage brute. Hum- 
 phry knew the peril of the encounter, and finding 
 the animal about to relax its hold of his flesh, he 
 seized it by the neck and held its head firmly to 
 the ground, while the townsfolk rushed immediately 
 to the spot, and with their weapons soon put an 
 end to all the danger. 
 
 “ Tha bee’st bitten, Master Humphry,” shouted 
 Malachy Carteret, as he drew his adze from the 
 
HUMPHRY PRACTISES ON HIMSELF. 299 
 
 head of the animal; “ran tha to Dr. Borlase di- 
 rectly, and ha’ the bite looked to, or tha life, poor 
 boy, a’n’t worth a dried pilchard.” 
 
 Then came Jan Penberthy the miller — as white 
 as plaster-cast in his working dress — and he, with 
 a cluster of others behind, were anxious in their 
 inquiries as to what was the nature of the wound, 
 while each had some novel and different remedy to 
 recommend. 
 
 Humphry, however, knew sufficient of his pro- 
 fession to be aware that it was no time for hesi- 
 tation ; so, while the eager throng crowded around 
 him, he raised the leg of his trousers, and observing 
 the marks of the animal’s teeth in his flesh, he 
 deliberately drew his knife from his pocket, and 
 there, upon the spot, cut out the lacerated part 
 without a wince. 
 
 This striking instance of the boy’s intrepidity 
 was hailed with wonder by the people about him, 
 and one and all were loud in their praises of his 
 courage and decision. Many who had known him 
 from a child rushed up and shook him warmly by 
 the hand, while others, who had been the com- 
 panions of his father, declared he was Robert 
 Davy’s own son every inch of him — indeed all 
 there had some encouraging word to say or some 
 kindness to proffer. 
 
 Humphry, however, was too sick and faint from 
 loss of blood to be able to listen to the remarks of 
 
300 
 
 THE WONDERS OF SCIENCE. 
 
 those about him ; so, having tied his handkerchief 
 round the wound, he begged Malachy Carteret to 
 help him home to Dr. Borlase’s. And as the little 
 carpenter curled the boy’s arm about his neck 
 Humphry limped along with Chloe at his side, who 
 kept looking up sadly in his face, as if she was 
 aware of all that had happened, while the boy ex- 
 claimed as he went, “ Thank God I have saved 
 your life, poor Chloe, even though it be at the ex- 
 pense of my own.” 
 
 Following in the wake of Humphry and Ma- 
 lachy walked many of the crowd — one carrying 
 the boy’s fishing-rod, another his jack-boots, and 
 another the basket of trout that Chloe had drppped 
 in the road ; and as they went along, they won- 
 dered among themselves whether Master Humphry 
 would get the better of the bite ; and some told 
 curious country tales as to how the poison had 
 remained in the blood for years afterwards, so that 
 a person’s life was never safe from it. 
 
 On reaching the surgery, Humphry found that 
 Mr. Borlase had been called to visit a patient in 
 the country that evening ; so, being left to his own 
 resources, he proceeded forthwith to apply some 
 lunar caustic to the wound himself, and having 
 done this, he begged Mrs. Foxell (who was fright- 
 ened to tears at the dangerous accident he had 
 met with) to make his excuses to her brother, the 
 doctor, when he returned, for the poor boy told her 
 
HUMPHRY PRACTISES ON HIMSELF. 301 
 
 he was anxious to reach his mother’s house before 
 the news of his having been bitten by a mad dog 
 was carried home, so that he might lighten her 
 alarms on his account. 
 
 Humphry, however, had barely taken leave of 
 Mrs. Foxell before Mrs. Davy herself rushed into 
 the surgery, half frantic with fear at what she 
 had heard ; and she no sooner caught sight of him 
 than she fell upon his neck, and wept and laughed 
 by turns, hysteric with the intensity of her emotion. 
 
 The boy endeavoured to assuage her, assuring 
 her that from the promptness and vigour of the 
 remedies he had applied there was little cause for 
 alarm. But to no avail : the poor woman was 
 satisfied her darling boy was doomed to the most 
 frightful of all deaths sooner or later, saying, “ that 
 if she was deprived of him her cup of bitterness 
 would be full indeed.” Then the heavy privations 
 she had already suffered in life rose again to her 
 mind, and in the agony of her despair at the 
 calamity which now threatened her she wrung 
 her hands, and cried aloud to God to have mercy 
 upon her. 
 
 Nor could she in any way be soothed until the 
 lad told her it was necessary for him at such a 
 time to remain in perfect quietude, and that the 
 least excitement might develope the very symp- 
 toms which she dreaded. 
 
 This had the desired effect. Such was her love 
 
SC2 THE WONDERS OF SCIENCE. 
 
 and care of the boy, that not another tear did she 
 afterwards shed in his presence ; but, dismissing her 
 own trials, she talked to him only of the subjects 
 she knew he delighted in ; and, when she had him 
 removed to her own house, she sat by his bed, day 
 after day and night after night, reading to him from 
 works on the different sciences till his eyes were 
 closed in sleep, and then the poor widow would 
 fall upon her knees, and with her pent-up tears 
 streaming in secret from her eyes, and her voice 
 choked with her sobs, pray the Great Ruler of All 
 to spare the only protector left her. 
 
THE FIRST SUN-PlCTUllES. 
 
 303 
 
 CHAPTER XIII. 
 
 THE FIRST SUN-PICTURES. 
 
 Humphry remained confined to his bed for many 
 weeks, and every day his mother dreaded seeing 
 some development of the symptoms which gene- 
 rally ensue from the bite of so rabid an animal ; 
 but the boy assured her, again and again, that, 
 owing to the promptitude of the remedies he had 
 applied, there was no cause for alarm. 
 
 While the youth was still a prisoner in his room, 
 a gentleman came to lodge at the house, and Hum- 
 phry, to his great delight, learnt, in a few days 
 afterwards, that the new lodger was no less a person 
 than Mr. Gregory Watt, son of the celebrated 
 James Watt, the inventor of the present steam- 
 engine. 
 
 It did not take long before the two became ac- 
 quainted, and then Humphry ascertained that the 
 young Mr. Watt had but recently quitted the Uni- 
 versity of Glasgow, and had been recommended by 
 
304 
 
 THE WONDERS OF SCIENCE. 
 
 his physicians, owing to his declining state of 
 health, to reside for some time in the West of 
 England ; hence the cause of his visit to Pen- 
 zance. 
 
 Nor was Humphry long in discovering that the 
 mind of his new friend was enriched beyond his 
 age with science and literature, and that he pos- 
 sessed, like himself, a spirit devoted to the acqui- 
 sition of knowledge, and soaring far above the 
 little vanities and distinctions of the world. The 
 two kindred spirits, therefore, soon contracted an 
 intimacy of the warmest nature ; and this ultimately 
 ripened into a friendship which continued to the 
 period of Mr. Watt’s premature dissolution. 
 
 Mr. Gregory Watt felt not a little astonished, 
 on being introduced to the son of his landlady, 
 to find him shortly afterwards speaking upon sub- 
 jects of metaphysics and poetry ; for when Mr. 
 Watt spoke to him of the courage he had dis- 
 played at the time of the accident in excising the 
 wounded parts of his leg, Humphry confessed “ that 
 he had no belief in the existence of pain, whenever 
 the energies of the mind were directed to counter- 
 act it.”*' “For,” went on the boy, “in states of 
 profound attention, all perception of external things 
 fades from the mind ; the clock in the room ticks, 
 and we hear it not ; persons enter the apartment, 
 
 * See Dr. Paris’s “ Life of Davy,” p. 12. 
 
THE FIRST SUN -PICTURES. 
 
 305 
 
 and their presence is unheeded by us. And if by 
 the intensity of the intellectual operations the senses 
 can cease performing their functions in the one 
 case, why not in the other ? Martyrs at the stake 
 have, while in deep prayer, held their hand un- 
 moved in the flames, and who can say that the 
 very fervour of their heavenly aspirations did not 
 deprive them of all sense of pain for the time 
 being ?” 
 
 Mr. Gregory Watt, however, had but little taste 
 for metaphysical discussions ; and, smiling at Hum- 
 phry’s stoicism, sought to divert the conversation 
 into a more congenial and practical channel. 
 
 The steam-engine that had been recently set up 
 at the Wherry Mine by Mr. Watt’s father became 
 the theme of their converse ; this soon led to com- 
 ments on the theory upon which its powers de- 
 pended, and then Humphry’s companion was sur- 
 prised to find that a youth, who had been brought 
 up in an obscure town in Cornwall, was as well 
 acquainted with the doctrine of “ latent heat” — and, 
 indeed, the whole science of caloric — as he him- 
 self, who had been reared, as it were, in a factory, 
 where the workings of it were every day visible. 
 
 The new laws of combustion naturally followed 
 as the next subject of discussion, when Humphry 
 observed, “ that he would undertake to demolish 
 the French theory in half-an-hour and so saying, 
 he rapidly ran over the experiments he had per- 
 
 x 
 
306 
 
 THE WONDERS OF SCIENCE. 
 
 formed, to prove the falsity of Lavoisier’s notions 
 respecting the origin of heat during the burning of 
 substances.* 
 
 The lad had now touched the true chord, and 
 the interest of Mr. Watt becoming more excited, 
 he conversed with young Davy upon his chemical 
 pursuits, and was at once astonished and delighted 
 at his sagacity ; so that the couple — congenial in 
 taste — already began to feel a growing friendship 
 for each other. 
 
 Humphry had quitted his chamber, but was still 
 confined to the house, from his inability to walk, 
 when Mr. Watt — who had now known the youth 
 long enough to be proud of his acquaintance — re- 
 turned from his morning’s stroll along the sea- 
 shore, in company with two friends whom he had 
 met in the town. 
 
 The gentlemen proved to be Mr. Josiah Wedg- 
 wood, the eminent potter of Staffordshire, and his 
 brother Thomas, who was alike distinguished for 
 his scientific abilities. 
 
 The learned potter was not long in Humphry’s 
 company before he discovered the high merits of 
 the lad ; nor was he a little pleased when he found 
 that the young Cornish apothecary knew all about 
 the pyrometer he had invented for measuring high 
 
 * See Dr. Paris’s account of Davy’s first interview with 
 Gregory Watt, p. 35. 
 
THE FIRST SUN-PICTURES. 
 
 307 
 
 degrees of lieat by the contraction of a ball of 
 clay ; and the old gentleman found considerable 
 delight in explaining to the boy the various pro- 
 cesses concerned in the manufacture of earthen- 
 ware and porcelain, telling him anecdotes as to 
 how Bernard Palissy — who was the first to dis- 
 cover the means of giving a glaze to the baked clay 
 — had been reduced to such poverty by his experi- 
 ments, that he was forced to burn the doors, and 
 even the boards, of the house in which he lived, in 
 order to get a supply of fuel for his furnaces ; and 
 how he afterwards amassed an immense fortune by 
 the invention, and ultimately died in the French 
 Bastille, a martyr to the Protestant creed, which 
 he had espoused. Mr. Wedgwood added that, 
 “ When we eat our food we little think of the 
 labour and privations that have been endured in 
 order to give a glassy surface to the plates and 
 dishes upon which it is served ; for but few are 
 aware that, previous to this invention, the ordi- 
 nary earthenware articles were more like tiles than 
 our present crockery.” 
 
 Then Mr. Wedgwood talked with the youth 
 about the rocks, inquiring whether he had ever 
 noticed any of the finer species of clay in those 
 parts, and was surprised to find how closely the 
 boy had marked the changes in the soil ; for 
 Humphry told him “he had observed that the 
 
308 
 
 THE WONDERS OF SCIENCE. 
 
 felspar in the granite decomposed long before either 
 the mica or the quartz, and that it was chiefly by 
 the action of the atmosphere upon this same fel- 
 spar that the huge granite rocks became disin- 
 tegrated, or broken up ; and that, as the felspar 
 consisted principally of clay in the purest form, he 
 fancied that some advantage might be taken of 
 this in producing a finer species of porcelain than 
 had yet been manufactured in this country.” 
 
 The old gentleman thanked Humphry for his 
 suggestion, and warmly praised him for his obser- 
 vation and sagacity ; whereupon the youth pro- 
 mised, immediately that his leg would permit of his 
 accompanying him, to point out to Mr. Wedgwood 
 the places where he had noticed the finest deposits 
 of felspar to occur. 
 
 The conversation then changed to a subject that 
 Mr. Josiah Wedgwood said “he had no doubt 
 would be highly interesting to one of Humphry’s 
 turn of mind.” The old gentleman told the boy 
 how his brother Thomas had discovered a means 
 of copying pictures upon glass, and even of fixing 
 the images of the camera obscura , by the action of 
 light ; “ so that,” he said, “ the sun itself could be 
 made to turn artist, and to produce a represent- 
 ation of an object that no human hand could pos- 
 sibly rival.” 
 
 Humphry was enraptured with the new wonder, 
 
THE FIRST SUN-PICTURES. 
 
 809 
 
 and more eager than ever to learn all about it ; so 
 he begged Mr. Thomas Wedgwood to explain to 
 him the whole process. 
 
 44 I should tell you, then,” said the potter’s 
 brother, “ that it has been long known to chemists 
 that a solution of nitrate of silver (called lunar 
 caustic in the shops), when washed over a sheet of 
 paper — although it does not undergo any change 
 while kept in a dark place — will speedily change 
 colour on being exposed to daylight, and that then 
 it passes through different shades of grey and 
 brown, and ultimately becomes nearly black. These 
 alterations in colour,” continued Mr. Thomas Wedg- 
 wood, 44 take place more rapidly according as the 
 light is more intense. In the direct beams of the 
 sun, two or three minutes are sufficient to cause 
 it to darken ; whereas in the shade, several hours 
 are required to produce the full effect. The light, 
 too, when transmitted through different-coloured 
 glasses, acts upon the nitrate of silver with dif- 
 ferent degrees of intensity. It is found, for in- 
 stance, that the sunbeams, when passed through 
 red or yellow glass (so that only red or yellow 
 light shall fall upon the paper), have very little 
 action upon the lunar caustic ; green glass, how- 
 ever, is more efficacious, while blue and violet 
 produce the most decided and rapid changes. 
 
 44 Now to make you clearly comprehend,” went 
 on the gentleman, 44 the reason of these changes, I 
 
310 
 
 THE WONDERS OF SCIENCE. 
 
 should tell you that nitrate of silver consists of 
 nitric acid (aquafortis) and silver,* and that if a 
 vessel of pure and colourless nitric acid be exposed 
 to the sun’s rays, it will become decomposed, so 
 that red fumes of nitrous acid will be evolved, and 
 these mixing partly with the liquid itself, will 
 shortly turn it to a reddish-brown tint. Well, the 
 same change takes place when the nitric acid is 
 combined with the silver, and so made to form 
 nitrate of silver. The consequence is, that as the 
 nitrous acid which is evolved is unable to combine 
 directly with the silver, the decomposed aquafortis 
 is dissipated in the form of vapour, while the silver 
 itself remains behind in the paper ; and in such an 
 extreme state of minute division, that the particles, 
 instead of being white, like ordinary silver, appear 
 black to our eyes.” 
 
 Humphry expressed himself delighted with the 
 explanation, and said he could now see how it was 
 possible to produce sun-pictures by such means. 
 Still he begged Mr. Wedgwood to proceed. 
 
 That gentleman then told Humphry that his 
 first attempt concerning the production of sun- 
 pictures, was to fix the evanescent images formed 
 by the camera obscura, but though he was able to 
 
 * For the sake of simplicity, the nitric acid is here made to 
 consist (according to the new theory) of N O + H (instead of 
 N O s + H O), and so to combine directly with the metal as 
 N O g + A g (instead of with the oxide as N O^ + OAg). 
 
THE FIRST SUN-PICTURES. 
 
 311 
 
 impress these upon paper in a bright sunlight, he 
 found that he could not produce them in any mode- 
 rate time in ordinary daylight ; so that, from the 
 length of time required before the impression was 
 taken, the effects of light and shade had materially 
 altered. “ With paintings on glass, however,” he 
 added, “ I have been more successful ; in order to 
 copy these I apply the solution of nitrate of silver 
 to leather, for this I find to be more readily acted 
 upon than paper — probably owing to the tanning 
 in the material. When the surface of leather is 
 thus prepared, I place it behind a painting upon 
 glass, and expose it to the solar light, when the 
 rays, being transmitted through the different parts 
 of the picture, produce distinct gradations of black 
 and white, according to the lights and shades in 
 the original; for where the light passes freely 
 through the glass, the colour of the nitrate of 
 silver, of course, becomes the deepest. By this 
 means, then, you will perceive that the lights and 
 shades of my picture are entirely reversed : all the 
 black parts in the original being left white in the 
 copy, since the light, being unable to pass through 
 these, cannot act upon the solution; while all the 
 white parts of the original, on the other hand, 
 become the blackest in the copy, owing to the rays 
 passing freely through the glass there, and so pro- 
 ducing the strongest effect. Accordingly, I am 
 
312 
 
 THE WONDERS OF SCIENCE. 
 
 obliged to have the original pictures painted, in the 
 first instance, with their lights and shades reversed, 
 or else I cover another glass with a thin coating of 
 isinglass, and apply the solution of nitrate of 
 silver to this ; so that, when I have transferred the 
 original picture by this means to a second plate 
 of glass, in which the lights and shades are the 
 direct opposite to what they are in nature, I 
 proceed to take a second copy of it — but this I do 
 upon leather, as before explained — and so obtain a 
 perfect reproduction of the original, with all the 
 lights and shades in their proper places. 
 
 “But the same method of copying,” proceeded 
 Mr. Wedgwood, “may be applied to other pur- 
 poses. It may be rendered subservient, for in- 
 ^jance, for making delineations of all such objects 
 as are partly opaque and partly transparent, such 
 as leaves and the wings of insects. For this pur- 
 pose it is only necessary to put the objects to be 
 copied between a plate of glass and the prepared 
 leather itself, when the sunlight, being more or less 
 intercepted by their forms, will leave the figures 
 accurately impressed upon the leather, so that they 
 will appear as beautiful white pictures upon a 
 black ground. There is, however,” added Mr. 
 Thomas Wedgwood, “one great defect connected 
 with the production of sun -pictures by the means I 
 have described, and this consists in the impossi- 
 
THE FIRST SUN-PICTURES. 
 
 313 
 
 bility of fixing them so that they shall be no longer 
 susceptible of being darkened when exposed to the 
 light. I have already tried several methods of 
 obviating this difficulty. I have covered the sun- 
 pictures with a thin coating of varnish, but to no 
 purpose, for they darken almost as rapidly with 
 the varnish over them as others do without it. 
 Again, I have submitted the pictures to frequent 
 washings, in the hopes of dissolving out of the 
 paper or leather all the undecomposed nitrate of 
 silver ; yet, even after this, a certain portion of the 
 active matter still adheres to the white parts of the 
 sun -picture, and so causes them to blacken all over 
 on being exposed to the light. The consequence 
 is, that the pictures produced by the action of the 
 sun must, in order to be preserved, be examined 
 always in the dark, and be kept continually in some 
 place where no light can penetrate.” 
 
 Humphry no sooner heard this than he suggested 
 a number of expedients by which he fancied the 
 difficulty might be overcome ; and as the lad ex- 
 plained his reasons for the various methods he pro- 
 posed, both Mr. Wedgwood and his brother were 
 as astonished at the extent of the boy’s knowledge, 
 as they were delighted with the acuteness of his 
 sagacity. 
 
 The evening was passed in examining a portfolio 
 of the sun-pictures that Mr. Thomas Wedgwood 
 had brought with him, and Humphry grew so 
 
314 
 
 T HE WONDERS OF SCIENCE. 
 
 charmed with the then entirely novel process of 
 “ photography ” that he declared he would not rest 
 until he had investigated the matter himself, and 
 ascertained experimentally whether any means 
 could be found of rendering the pictures perma- 
 nent. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 315 
 
 CHAPTER XIV. 
 
 THE WONDERS OF THE REFRACTION OF LIGHT. 
 
 Our young hero was still too weak to leave the 
 house, for the wound in his leg was of so dan- 
 gerous a description that Mr. Borlase had strictly 
 enjoined him to take as little exercise as possible ; 
 consequently, while Humphry’s evenings were 
 passed in conversation with young Mr. Watt, and 
 occasionally the Wedgwoods, his mornings were 
 spent in his chamber alone, so that he was glad to 
 resort to study as a means of enlivening his soli- 
 tude. 
 
 Still the lad wanted some incentive to stir him 
 to enter upon a fresh branch of science. This, 
 however, he had now found in the wonderful pho- 
 tographic impressions Mr. Wedgwood had shown 
 him, and he was eager to make himself acquainted 
 with the laws of the mysterious principle by which 
 they had been obtained. 
 
316 
 
 THE WONDERS OF SCIENCE. 
 
 The contemplation of the sun-pictures naturally 
 led Humphry to think of the more transient pic- 
 tures formed in the camera obscura by the light ; 
 and he passed from the fixing of the images to the 
 consideration of the conditions by which the images 
 themselves are produced. 
 
 “ How comes it,” he mentally inquired, “ that a 
 piece of glass, merely because it is rounded on 
 one or both sides, is able to copy the forms and 
 colours of external objects ? And why do several 
 of such glasses, in combination, bring the images of 
 even the most distant things so close to us, that we 
 are enabled to make out their minutest parts ? ” 
 Humphry knew that the effect could arise only 
 from some alteration in the direction of the rays of 
 light as they passed through the glass itself ; and, 
 accordingly, he determined to set to work and dis- 
 cover the precise change that a luminous ray under- 
 goes on traversing different substances. 
 
 In the first place, however, it was necessary to 
 determine what was the natural direction of a 
 ray of light emitted by a luminous body. 
 
 For this purpose Humphry — who was still un- 
 able to undergo the exertion of arranging his own 
 experiments — had to avail himself of the assistance 
 of his sister Kitty ; and so pleased was the girl with 
 the office, that she readily gave up to her brother 
 every moment she could spare from her household 
 duties. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 317 
 
 Kitty Davy was some two years younger than 
 Humphry himself, so that they had been infant 
 playmates together, sharing the same toys and 
 taking parts in the same childish gambols. It was 
 to Kitty, too, that the boy had first recounted the 
 fairy stories he loved to invent ; and when, in his 
 after-youth, Humphry compounded his celebrated 
 “thunder-powder,” Kitty invariably aided him in 
 the manufacture of the composition : so that each 
 year had served to increase the love which, from 
 the remembrance of the pleasures they had enjoyed 
 together, had been begotten almost with the dawn 
 of memory itself. 
 
 Kitty was now budding into womanhood. She 
 had grown so tall within the last year, that her 
 figure was spare, and not particularly comely ; 
 while the curls, which once fell, with childish 
 beauty, in tortuous profusion about her neck, had 
 now been displaced, and the hair twisted into the 
 more womanly, but less gainly, protuberance at the 
 back. This style of head-dress had long been a 
 point of ambition with the young lady, and now 
 that she had risen to the dignity of wearing her 
 hair like her mother, Miss Kitty had grown to 
 fancy that she was no longer a child. 
 
 Nor was she. The increasing strength of her 
 affection for her brother showed that her woman’s 
 nature was developing, and she seemed to cling 
 to Humphry and her mother with a new ten- 
 
318 
 
 THE WONDERS OF SCIENCE. 
 
 derness, as if she needed some one to heap her 
 strengthened love upon. The doll upon which she 
 had, until the last year or so, bestowed her caresses, 
 had been given to one of her younger sisters ; and 
 now she appeared to take almost a mother’s pride 
 in tending little Johnny, her brother, instead. 
 
 Humphry during his illness had been constantly 
 “ nursed” by her, and now that she was allowed to 
 officiate in the kitchen, the girl loved to surprise 
 him each day with some new posset or jelly which 
 she had prepared for his gratification. She had read 
 to him, too, so long by his bedside from the scientific 
 books which her brother loved to listen to, that, 
 aided by his explanations of the more difficult parts 
 of the subject, she herself had acquired a slight 
 knowledge of the phenomena of the universe : so 
 that, while assisting him in his experiments, she felt 
 almost the same taste for the work as Humphry 
 did, and was not a little delighted when the hour 
 came for her to take her accustomed post in her 
 brother’s sick chamber. 
 
 Humplny, as we said, was intent upon disco- 
 vering the natural direction of a ray of light pro- 
 ceeding from a luminous body. With this view 
 he got Kitty to close the shutters so as to com- 
 pletely darken the room, and then to pierce a fine 
 hole through them. This being done, Humphry 
 pointed out to the girl that the beam was in a 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 319 
 
 perfectly straight line — for the course of it was 
 rendered plain by the little particles of dust that 
 floated in the atmosphere, flashing, as they danced 
 in the ray, like so many tiny fire-flies. Then as 
 Kitty wheeled her brother’s chair so that the light 
 fell directly upon his eye, the boy could see the sun 
 itself shining through the hole ; thus proving that 
 the beam proceeded in a direct straight line from 
 the orb of light to him. 
 
 The next step was to procure a flexible tube, 
 and with this held straight before the eye, Hum- 
 phry could still distinguish the sun through the 
 hole in the shutter, though when the tube was 
 curved the effect was totally different, for then no 
 light at all could be perceived. 
 
 Kitty was not a little delighted with the demon- 
 stration that a ray of light proceeds in a straight 
 line ; and Humphry, to make her understand, as 
 well as to prove to himself experimentally, that all 
 luminous bodies projected an infinity of such 
 straight rays in every possible direction , bade the 
 willing girl fetch him the rushlight and shade 
 from below. 
 
 While the shutters were still closed the candle 
 was lighted, and then Humphry pointed out to his 
 sister how the little luminous circles that were 
 spattered over the wall all round the room, as the 
 light passed through the holes in the shade, showed 
 that the rays proceeded from it in every direc- 
 
320 
 
 THE WONDERS OF SCIENCE. 
 
 tion ; and that they travelled in a straight course 
 was easily proved, by covering with the finger 
 any one of the holes in the shade, when the lumi- 
 nous circle on the wall, which was in a direct line 
 with the hole, and the flame became immediately 
 obscured. 
 
 It was plain, then, that a ray of light travelled 
 naturally in a straight line. Still, as a further 
 proof of this phenomenon, Humphry threw the 
 shadow of an opaque body, of a certain size, upon 
 a white screen, and there measured its dimensions. 
 Having cut a piece of millboard, exactly a foot 
 square, he placed it 1 foot distant from the flame 
 of a candle, and then arranging the screen at 
 double the distance, or 2 feet from the light, he 
 found upon measuring the shadow of the mill- 
 board that it was exactly (2x2) 4 times larger 
 
 than the millboard. When the screen was 3 
 feet distant from the candle, or 3 times as far 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 321 
 
 from the light as the millboard, the shadow was 
 ascertained to be (3x3) 9 times larger than the 
 surface from which it was projected ; while at the 
 
 distance of 4 feet, the dark space upon the screen 
 was discovered to be (4x4) 16 times greater than 
 the millboard itself. 
 
 This effect could arise solely from the rays of 
 the candle proceeding in a straight direction, as 
 will be rendered evident by the preceding dia- 
 grams ; where it will be seen that the opaque 
 body, interposed between the light and the screen, 
 
 T 
 
322 
 
 THE WONDERS OF SCIENCE. 
 
 prevents the rays which fall upon it reaching the 
 screen itself, so that a dark space appears upon the 
 latter, as many times larger than the opaque body, 
 as the distance of the screen from the candle is 
 greater than the body projecting the shadow ; for 
 it is manifest, that if a series of right lines be 
 drawn from the luminous point to the edges of 
 the opaque body, and thence to the screen itself, 
 they will exactly circumscribe a space whose di- 
 mensions will be proportional to the distance of 
 the one to the other. 
 
 “Well,” said Humphry to his sister, “we now 
 see that luminous bodies emit rays of light in all 
 directions , and that each ray from them proceeds 
 in a straight line, while those substances which 
 are called opaque prevent, when placed before the 
 light, the rays from reaching other substances be- 
 hind them — the rays, in such cases, being stopped 
 or intercepted. Some bodies, however,” added 
 the boy, “ are capable of transmitting the rays of 
 light ; that is to say, they allow the beams to pass 
 through them, and these are, therefore, termed 
 transparent ; since, unlike opaque bodies, they pro- 
 ject no shadows when placed between the light and 
 other bodies. Let us now see what occurs when a 
 ray of light passes through a transparent body.” 
 
 Accordingly, Humphry procured a small open 
 vessel, in one of the sides of which there was a hole 
 near the top, large enough to admit the light from 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 323 
 
 a candle. The lad then proceeded to ascertain the 
 exact place where the ray of light from the flame 
 fell at the bottom of the vessel ; and found that, 
 when the vessel was empty and the candle placed 
 at a short distance from 
 the hole, there was a 
 small circle of light 
 formed at the bottom, 
 which was, of course, in 
 a direct line with the hole and the flame, as here 
 shown. 
 
 Having then set a mark at A, where the circle 
 of light appeared, he directed Kitty to pour water 
 into the vessel until it was half full ; and when 
 she had done so, he noticed that the ray of light 
 from the candle no longer fell upon the same spot as 
 it did when the vessel was empty, but at a little dis- 
 tance nearer the candle, so that it was plain that 
 
 the ray, instead of pro- 
 ceeding in a straight 
 line as before, had, in 
 passing through the 
 water, been bent down 
 out of its usual course , 
 
 in the manner indicated at B. 
 
 “You see, then,” remarked Humphry, “that a 
 ray of light, when it falls in a slanting direction 
 upon a transparent body, no longer travels on in 
 a straight line , but is refracted ,” as it is called; 
 
324 
 
 THE WONDERS OF SCIENCE. 
 
 44 or bent out of its previous course , at a certain 
 angle . Consequently, if the spot B was a fish lying 
 at the bottom of a river, it would be seen by a 
 person on the shore in the direction of the point 
 A ; and thus it would appear out of its true place, 
 and, in order to strike it with a spear, we should 
 have to direct the weapon at a spot nearer to us 
 than where the fish seemed to be lying.” 
 
 Then her brother told her that it was for the 
 same reason that a straight stick appeared to be 
 crooked when half immersed in a pool of water, and 
 a crooked stick a straight one under the same cir- 
 cumstances ; “ for,” said he, “ if instead of the 
 straight ray of light we imagine a straight stick to 
 be passed through the hole, so that the point of it 
 may be at the spot A, it is plain that in the water 
 the end of the stick will appear at B, since the part 
 of it which is immersed will seem to be bent in that 
 direction ; whereas if the stick itself be bent, so 
 that the end of it is at B, it will, for the same 
 reason, appear when in the water at A, and, con- 
 sequently, seem to be perfectly straight. 
 
 The next step was to try and measure the degree 
 of refraction, or, in other words, to find out how 
 much a ray of light was bent out of its usual 
 course on passing through different transparent 
 substances. 
 
 Accordingly, Humphry procured his old school- 
 slate, and having managed, with Kitty’s assistance, 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 325 
 
 to mount this on a heavy pedestal, he described 
 upon the slate a circle with two diameters, each 
 perpendicular to the other ; then having bored a 
 hole in the centre, he fitted into it a large cork ; this 
 had a straight tube afterwards let into it, so that 
 the tube, by means of the cork in the middle, could 
 be moved freely round the 
 circle, turning, as it did, upon 
 the centre of it. The whole 
 apparatus was then inserted 
 in a vessel of water, so that 
 the fluid reached exactly to 
 the level of the horizontal 
 diameter, — thus, without touching the end of the 
 tube. 
 
 The youth then found, that when the tube A was 
 directly perpendicular to the surface of the water, a 
 ray of light, on passing down it, suffered no change 
 at all in its direction ; and that on placing a sixpence 
 in the water, exactly in a line with the perpendi- 
 cular diameter, B, it could be seen distinctly through 
 the tube, so that the rays from the coin, on quitting 
 the water, proceeded in the same straight course 
 as they had pursued while passing through the 
 fluid. 
 
 Hence it was evident that a ray of light, on 
 entering or quitting a refracting surface in a per- 
 pendicular line, is not refracted or bent out of 
 its course . 
 
326 
 
 THE WONDERS OF SCIENCE. 
 
 It was, different, however, when the tube was 
 slanted , instead of being 
 placed straight above the 
 surface of the water, for 
 when a ray of light passed 
 down it in that direction, 
 the ray was found to be re- 
 fracted, or bent out of a 
 straight course, as shown in the above dia- 
 gram. 
 
 Now the precise direction of the refracted ray 
 having been marked upon the slate, the apparatus 
 was removed from the water, and the distance of 
 the tube A from B, the vertical diameter, measured, 
 as well as the distance of the refracted ray, a , 
 from the same perpendicular line, b , and it was 
 then found that the refracted ray, a , was as near as 
 possible 3 inches from the diameter, b , while the 
 ray A, which passed down the tube, was as much as 
 4 inches distant from B, the same line. 
 
 The tube A was then set at about 1^ inches 
 from the diameter B, and the apparatus replaced 
 in the water, when it was discovered that a ray of 
 light a , on passing down it, fell exactly at 1 inch 
 from b , the perpendicular line. 
 
 • Several other positions of the tube were after- 
 wards tried, and invariably with the same result : let 
 the tube be slanted as it might, the distance A . . . B 
 of the ray which passed down it, when compared 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 327 
 
 with the distance a . . . b of the refracted ray from 
 the perpendicular line, was always ascertained to 
 be in the same 'proportion , — viz. very nearly as 1* 
 to 1 ; or, more correctly speaking, when A . . . B, 
 the sine of the angle at which the ray entered the 
 water, was 1 i-, then a ... b, the sine of the angle 
 formed by the refracted ray, was exactly 1. 
 
 On referring to his books, Humphry found that 
 the number lx 3 o 3 o 6 o constituted what was termed 
 the index of refraction for water. 
 
 On performing the same experiment with oil of 
 turpentine the lad discovered, that when the ray 
 which passed down the tube was almost as much 
 as 1J inch distant from the perpendicular, the re- 
 fracted ray w^as 1 inch distant from the same 
 line ; whereas with sulphuret of carbon (though 
 with this the experiment was performed on a 
 smaller scale), when the ray passing down the 
 tube was 1-| inch removed from the perpendicular 
 — the refracted ray was still only 1 inch away 
 from the same line. 
 
 Humphry then consulted a table of the refrac- 
 tive power of different bodies, and learned that 
 hydrogen gas is the least refractive of all known 
 substances, (that is to say, a ray of light passing 
 through this gas is bent down by it out of its 
 previous course, less than by any other known 
 body,) and that the diamond has very nearly the 
 greatest refractive power of all, while the refrac- 
 
328 
 
 THE WONDERS OF SCIENCE. 
 
 tion of the air in its ordinary state is only 294 
 millionths greater than that of a vacuum . 
 
 This, however, is the refractive power of the 
 atmosphere at its average density near the earth’s 
 surface. But we learn from the barometer that 
 the density of the air diminishes as we mount 
 above the earth, and it has been found by experi- 
 ment that the refractive power of the atmosphere 
 decreases in proportion as it becomes more and 
 more rarified ; so that the atmospheric refraction 
 is greatest at the earth’s surface, and gradually 
 diminishes upwards, till the air becomes so rare 
 as to be able to produce scarcely any effect at all 
 upon the rays of light. 
 
 “ In order to understand 
 this,” said Humphry to his 
 sister, “ we must consider the 
 earth to be encased in a series 
 of shells, as it were, of atmo- 
 sphere, each of a less density 
 than the one below it, and, 
 consequently, of a less refractive power, — thus. 
 
 “ Let us suppose,” the lad continued, “ the round 
 ball in the centre here to represent the earth, and 
 the ring of atmosphere immediately next to it to 
 have a refractive power nearly 300 millionths greater 
 than a vacuum ; and the refractive power of the 
 ring, or shell of atmosphere immediately above this, 
 to be equal to only 200 millionths compared with 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 329 
 
 the same standard, while the power of the third 
 ring decreases to 100 millionths, and that of the 
 outer one to 50 millionths, whereas beyond this 
 no refraction whatever exists, so that the rays 
 moving through free space will continue in the 
 same line as that in which they are emitted from 
 the sun. What, then, will be the effect of such 
 a series of atmospheric shells upon a ray of light 
 passing through them ?” 
 
 To illustrate this Humphry drew the lines here 
 shown through the following diagram. 
 
 “ The orb S, outside the earth,” continued 
 Humphry, “ represents the sun below the horizon, 
 emitting, let us 
 suppose, his rays 
 in all directions. 
 
 These, passing 
 through free space, 
 proceed onwards 
 in a perfectly 
 straight line; and 
 one of them is here made to fall upon the outer 
 ring of the earth’s atmosphere, where it is slightly 
 refracted, or bent down out of its former course, so 
 that, instead of continuing in the direction of the 
 dotted line a, it proceeds through the upper portion 
 of our atmosphere in the direction of the unbroken 
 line, until it reaches a part of the atmosphere of 
 greater density — as in the second ring ; when, instead 
 
330 
 
 THE WONDERS OF SCIENCE. 
 
 of going on in tlie direction of the second dotted line 
 b , it is again refracted, or bent down, in a greater 
 degree than before. Then travelling onwards, it 
 reaches the third ring, where the atmosphere, being 
 of a still greater density, and, consequently, having 
 a greater refractive power, it is once more bent out 
 of its course c , and that to a still greater extent than 
 before. In this manner it ultimately arrives at a 
 stratum of atmosphere which immediately envelopes 
 the surface of the earth, and which, having the 
 greatest density of all, has the greatest refractive 
 power ; so that the ray, instead of continuing in 
 the direction c?, is here bent down more than ever, 
 and finally reaches the eye in the direction e , 
 which is in a direct line with the orb s. The 
 consequence is, that as every object is seen in the 
 direction that the ray has at the instant of arriving 
 at the eye , the sun itself appears to be above the 
 horizon when it is positively below it, as at S ; so 
 that, by the refraction of the atmosphere, the sun 
 is seen by us before he rises in the morning, and 
 for a short time after he sets in the evening. 
 
 Kitty was so astonished at the above conclusion, 
 that, though she understood the explanation, she 
 told her brother that she could hardly help doubting 
 the fact ; saying, “ it was almost the same as 
 asserting that we could see a thing that was out 
 out of sight.” 
 
 Humphry undertook to prove to his sister, by 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 331 
 
 experiment, that such a result was quite possible 
 by refraction. 
 
 Accordingly, he bade Kitty place the wash-hand 
 basin upon the table, and then having deposited a 
 shilling at the bottom of it, he told the girl herself 
 to recede from the table until the edge of the basin 
 obscured the shilling from her sight ; and when 
 Kitty assured him that she could no longer see the 
 coin, he poured some water into the vessel, and 
 immediately the girl exclaimed, — “ Dear, dear, 
 how odd ! I can see the shilling quite plainly 
 now.” 
 
 “ You perceive, then, Miss Kitty,” cried the boy, 
 triumphantly, “it is quite possible by refraction 
 to see things that are out of sight ; for the ray 
 from the shilling, A, on passing out of the water into 
 the air, is bent out of its 
 course, and you behold it 
 in the direction of the line 
 in which it enters your 
 eye, — thus, at a . 
 
 “ But far more wonderful things than this have 
 been brought to pass by the same means, Kitty,” 
 said her brother, delighted to impart the know- 
 ledge he had obtained from his books on this 
 subject, “and these are what are called mirages , 
 or optical illusions, produced by extraordinary re- 
 fractions in the atmosphere. For instance, the 
 cliffs on the French coast are 50 miles distant 
 
 a A 
 
332 
 
 THE WONDERS OF SCIENCE. 
 
 from Hastings, on the coast of Sussex, and they 
 are actually hidden from the eye by the convexity 
 of the earth ; that is to say, a straight line drawn 
 from Hastings to Calais or Boulogne would pass 
 through the sea. A year or two ago, however, 
 Mr. Latham, a Fellow of the Royal Society, who 
 was residing at Hastings, was surprised to see a 
 crowd of people running to the sea-side. Upon 
 inquiry into the cause of this, he was informed that 
 the coast of France could be seen by the naked 
 eye. He immediately went down to the shore to 
 witness so singular a sight, and there discovered 
 distinctly the French cliffs extending for some 
 leagues along the horizon, and so vividly that they 
 appeared to be only a few miles off. The sailors and 
 fishermen, with whom Mr. Latham walked along the 
 water’s edge, could hardly, at first, be persuaded 
 of the reality of the appearance ; but as the cliffs 
 gradually became more elevated, they were so con- 
 vinced that they pointed out to Mr. Latham the 
 different places they had been accustomed to visit : 
 such as the bay and the windmill at Boulogne, St. 
 Yallery, and other places on the coast of Picardy, 
 even as far as Dieppe, all the French shores ap- 
 pearing to the English sailors as if they were 
 sailing at a short distance from them towards the 
 harbours. With the aid of a telescope the French 
 fishing-boats were plainly seen at anchor, and the 
 different colours of the land upon the heights. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 333 
 
 together with the buildings, were perfectly dis- 
 cernible. The day when this occurred is said to 
 have been extremely hot, without a breath of wind 
 stirring, and the phenomenon continued visible in the 
 highest splendour until past 8 o’clock in the evening, 
 having been seen for three hours continuously.” 
 Some few years after the date of the above, a no- 
 less-marvellous optical illusion was seen by Pro- 
 fessor Vince of Cambridge, in company with another 
 gentleman, at Ramsgate. Between this town and 
 Dover there is a hill, on the farther side of which 
 stands Dover Castle, the summits of whose four 
 turrets can, in ordinary states of the atmosphere, be 
 just seen projecting above the brow, while the body 
 of the castle itself is usually hidden from view by 
 the rising earth between it and Ramsgate. On the 
 evening of the 6th of August, 1806, however, when 
 the air was very still, and a little hazy, not only 
 were the tops of the four towers of the castle 
 visible above the brow of the hill in the distance, 
 but the whole of the castle itself appeared trans- 
 ferred to the side of the hill next Ramsgate, as if 
 it had been really built there, instead of on the 
 other side of the eminence. This phenomenon was 
 so singular and unexpected that Dr. Vince, at 
 first sight, thought it an illusion. On continuing 
 his observations, however, he became satisfied that 
 what he saw was a real image of the castle. To 
 assure himself that it was no deception, he gave the 
 
334 
 
 THE WONDERS OF SCIENCE. 
 
 telescope to a gentleman who was with him at the 
 time, and who also saw the same clear image of the 
 entire castle, situate on the near side of the hill, as 
 the Doctor himself had witnessed. The view of the 
 castle was very strong, and well defined ; and 
 though the rays from the farther side of the hill 
 must, undoubtedly, have reached the eye at the 
 same time, still the strength of the image of the 
 castle itself so far obscured the background that it 
 made no sensible impression on the spectators. 
 Dr. Vince continued to observe the image for 
 about 20 minutes, during which time the ap- 
 pearance remained precisely the same, but rain 
 then came on, and he was prevented making any 
 further observations. 
 
 Humphry now began to study how, by means of 
 extraordinary refraction, inverted images of objects 
 might be seen in the atmosphere. 
 
 With this view he drew the subjoined diagram. 
 
 “ There, Kitty,” said the lad, as he laid down 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 335 
 
 his pencil and compasses, “ the drawing represents 
 a ship below the horizon, and concealed from 
 the eye of an observer by the convexity of the 
 earth. Well, if we suppose the refractive power 
 of the air at a little above the earth’s surface to be 
 less than it is at the surface itself, then the rays 
 which proceed upward from the ship, and which 
 never could, in the ordinary state of the atmosphere, 
 reach the eye in the position here shown, will be 
 refracted into curved lines, so that they will cross 
 one another ; while the ray which came from the 
 masthead, instead of being uppermost, will change 
 places with that coming from the hull, and becoming 
 the undermost of the two, will enter the eye in that 
 position : consequently, as every object is seen, as 
 I said before, in the direction of the rays at the 
 moment of their arriving at the eye , without refer- 
 ence to their previous course , an inverted image of 
 the ship will be perceived in the air, in the direction 
 of the dotted lines, and thus appear elevated above 
 the horizon.” 
 
 Kitty said she could hardly follow the explana- 
 tion, and wished to know whether her brother 
 could not devise some experiment in proof of it. 
 
 After a few moments’ consideration, Humphry 
 requested his sister to fetch him a square phial, 
 and to make him a little clear syrup with some 
 lump-sugar and water. When this was prepared, 
 the boy poured a small quantity of the syrup into 
 
336 
 
 THE WONDERS OF SCIENCE. 
 
 the phial, and upon this again he poured very 
 carefully an equal quantity of pure water, so that it 
 might float upon the syrup. Now the syrup, being 
 a fluid of greater density than the water, had a 
 proportionately greater refractive power, and as the 
 two combined with each other they formed strata, 
 having different refractive powers, the same as those 
 which had been supposed to exist in the atmosphere 
 at certain times, at a little distance above the surface 
 of the earth. Then having printed the word Syrup 
 upon a card, Humphry held this behind the bottle, 
 and the letters were seen erect through the stratum 
 of syrup at the bottom, but upside down at the part 
 where the syrup was mixing with the water, 
 and erect again through the layer of water itself 
 at the top. 
 
 After this the lad poured the same quantity of 
 spirits of wine carefully over the water itself, so 
 that the spirit being lighter than this might float 
 above this again ; and then having printed the word 
 Spirit on the upper part of the same card, the 
 \ letters of this were seen erect through the layer of 
 water, but topsy-turvy at the part where the spirit 
 ; and water were mingling, and in their proper form 
 through the uppermost stratum of spirit itself. 
 
 Humphry afterwards produced the same effect 
 by holding a heated iron above a tumbler of water, 
 so that the upper surface of it became warmed 
 while the lower remained cold, and the portion in 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 337 
 
 the middle became tepid. The heat, therefore, ex- 
 panded, and so rendered rarer the upper portions of 
 the liquid; and as it forced its way downwards, 
 produced strata of different densities, and, conse- 
 quently, of different refractive powers. The result 
 was, that on looking through the glass vessel three 
 images were seen as before ; the upper and the 
 lower ones —which arose from the rays passing 
 through the colder and the warmer strata, being 
 erect — and the middle one, or that which pro- 
 ceeded from the rays passing through the portion 
 in the middle, being inverted, — as previously ob- 
 served. The same effect may be produced by 
 looking along the side of a red-hot poker, at an 
 object 10 or 12 feet off, when an inverted image 
 will be seen at the distance of about |ths of an 
 inch from the line of the poker, and an erect image 
 within and without this. 
 
 The youth, having now demonstrated to his 
 sister how it was possible to produce three distinct 
 images, and one of these inverted, from the same 
 object, when seen through strata of different den- 
 sities, proceeded to recount to Kitty stories of 
 similar phenomena observed at sea. He told her 
 how Dr. Yince had seen at Ramsgate a ship whose 
 topmasts only were visible above the horizon, while 
 over this, in the air, two images of the complete 
 ship were observed, the uppermost being erect , and 
 the under one inverted , with the pennant from the 
 
 z 
 
338 
 
 THE WONDERS OF SCIENCE, 
 
 masthead of the inverted image nearly touching that 
 from the real ship, seen peeping above the horizon. 
 This was distinctly visible through the telescope ; 
 the sea appearing between the two ships in the 
 air, as here represented : — 
 
 “ As the ship rose to the horizon,” said Hum- 
 phry, “ the upper image gradually disappeared, and 
 while this was going on the lower and inverted 
 image as gradually descended ; but the mastheads 
 of the real and the spectral inverted ship never 
 exactly touched. On the real ship becoming en- 
 tirely visible, the aerial images were found to have 
 been perfect representations of it, even though the 
 
THE WONDERS OF THE REFRACTION OF LIGHT. S39 
 
 whole of the vessel at the time must have been 
 concealed below the horizon.” 
 
 There is, however, it may here be added, a still 
 more marvellous story in connexion with this part 
 of the subject, though it occurred at a more recent 
 date than that recounted by Humphry. During a 
 voyage to the coast of Greenland in the year 1822, 
 Captain Scoresby, having seen an image of an in- 
 verted ship in the air, directed his telescope to it, 
 and was able to discover that it was his father's 
 vessel, which was at the time below the horizon , and 
 cruising in a neighbouring inlet . “ The image,” 
 
 says the captain, “ was so well defined, that I could 
 distinguish by a telescope every sail, the general 
 6 rig of the ship,’ and its particular character, inso- 
 much that I confidently pronounced it to be my 
 father’s ship the ‘Fame,’ which it afterwards 
 proved to be ; though, on comparing notes with my 
 father, I found that our relative position at the 
 time gave our distance from one another 30 miles, 
 which is about 17 miles beyond the horizon, and 
 some leagues beyond the limit of direct vision. I 
 was so much struck by the peculiarity of the cir- 
 cumstance,” adds the captain, “ that I mentioned it 
 to the officer of the watch, stating my full con- 
 viction that the ‘Fame’ was then cruising in the 
 neighbouring inlet.” 
 
 The same officer, while navigating the Green- 
 land sea in 1820, saw the images of several ships 
 
340 
 
 THE WONDERS OF SCIENCE. 
 
 in tlie air. Some of these were double, and in- 
 verted, while along with them there appeared aerial 
 images of the ice, in two strata; the highest of 
 which had an altitude of a quarter of a degree. 
 
 The representation of ships in the air by un- 
 equal refraction has, no doubt, given rise in early 
 time to the superstitions of phantom-ships, which 
 are always said to sail in the eye of the wind, and 
 to plough their way through the sea when there is 
 not a breath of wind to ruffle its surface. The 
 story of the “ Flying Dutchman” had, probably, 
 a similar origin ; and the legend of the wizard 
 beacon-keeper of the Isle of France, who saw in 
 the air the vessels bound to the island long before 
 they were visible in the horizon, doubtlessly arose 
 from the man’s observation of some such phe- 
 
 nomena. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 341 
 
 CHAPTER XV. 
 
 THE WONDERS OF THE REFRACTION OF LIGHT 
 ( continued ). 
 
 Young Humphry now sought to discover the cir- 
 cumstances upon which the formation of images, 
 or pictorial representations of objects, depends. 
 
 “ In the first place,” said he to his sister, “ you 
 must bear in mind that all objects throw off 
 from them, in all directions, rays of light, which 
 are of the same colour as the objects them- 
 selves. The soldier’s coat appears red to us, be- 
 cause it sends red rays to the eye ; the fields are 
 green, because they emit rays of green light; and 
 the summer clouds are white, because the light 
 they reflect to us is of that colour . Indeed every 
 flower, whatever may be its tint, is seen by us 
 coloured as it is merely because the rays of light 
 proceeding from it are of the same hue as the 
 flower itself appears in our eyes” 
 
342 
 
 THE WONDERS OF SCIENCE. 
 
 Kitty told Humphry that she could hardly com- 
 prehend this ; saying, “ that the pattern of the 
 paper on the wall was green and yellow, and yet, 
 let her look at it in whatever way she might, 
 she could see no green and yellow rays coming 
 from it.” 
 
 Her brother, however, assured her that, if no 
 rays from the paper entered her pupil, she would 
 not be able to see it at all ; that is to say. the 
 wall would appear absolutely black in her eyes, 
 whereas, if the rays it reflected were colourless , it 
 would seem perfectly white to her. 
 
 “ In ancient times,” continued Humphry, “ it 
 was believed that the eye itself had some peculiar 
 power of emitting light, and thus of distinguishing 
 objects by its own agency ; but now we know that 
 no such power resides in the organ of sight, the 
 eye being almost passive during vision, and see- 
 ing only those objects which emit or reflect rays 
 of light to it: for it is merely by such rays of 
 light entering the pupil, and forming a picture of 
 the object at the back of the eye, that we are 
 enabled to distinguish the forms, as well as the 
 colours, of the things around us. So you must 
 bear in mind, Kitty,” he added, “ that the figures 
 and tints which you see come to your eye , instead 
 of your eye sending out anything to them ; for, 
 were it otherwise, you would be able to see with- 
 out any light at all.” 
 
TllE WONDERS OF THE REFRACTION OF EIGHT . 
 
 PofJC 313 . 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 343 
 
 Humphry then applied himself to prove, experi- 
 mentally, that all objects send off rays of light of 
 the same colour as themselves. 
 
 Accordingly, he took an empty cigar-box, and 
 having drilled a fine pin-hole at one end of it, he 
 bored another small hole in the lid — the latter being 
 for the purpose of looking through. Then, inside 
 the box, at the end opposite the pin-hole, he pasted 
 a piece of white paper, and placed a rose-tree at 
 some short distance in front of the box itself, so 
 that the rays of light from the plant might pass 
 through the pin-hole, and be projected upon the 
 white paper at the farther end of the dark box. 
 
 The arrangement being complete, he bade Kitty 
 apply her eye to the hole in the lid, and tell him 
 what she saw. 
 
 “ Dear, dear ! ” cried the astonished girl, “ I 
 declare if there isn’t a little tiny picture of the 
 rose-tree painted on the paper inside the box. It 
 isn’t very plain though, Humphry ; but I can just 
 see patches of red for the roses, and patches of 
 green for the leaves.” 
 
 “ Yes,” said her brother, “ and how could the 
 colours come there, unless the plant itself was 
 giving off different tinted rays from its leaves 
 and flowers ?” 
 
 “ But, Humphry,” the girl exclaimed, as she con- 
 tinued gazing through the hole, “ I do believe it’s 
 
344 
 
 THE WONDERS OF SCIENCE. 
 
 upside down ; for the patches of red that I see are 
 below the green, and ill the rose-tree itself the 
 dowers are up above, and the leaves underneath. 
 How very strange !” 
 
 The lad having had a peep himself at the image, 
 proceeded to explain to Kitty the reason of the pic- 
 ture appearing inverted. 
 
 With this view he drew the annexed dia- 
 gram : — 
 
 “ The rose-bush,” said he, “ is sending off rays 
 of light in all directions. Well, let us suppose two 
 of these rays to pass through the pin-hole in front 
 of the dark box, one coming from the top, and 
 another from the bottom of the plant. Now the 
 consequence would be, that the two rays, on 
 passing through the pin-hole, would cross each 
 other ; so that the one which was uppermost would 
 be transferred to the lower part, and that which 
 was originally the bottom ray take the place oi 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 345 
 
 the top one. Hence it is plain that the image, or 
 picture, of the object must appear upside down.” 
 
 Kitty was perfectly satisfied with the explana- 
 tion, but, wishing to see the picture of the rose 
 more plainly upon the paper, she asked Humphry 
 whether he could not admit more light into the 
 box. 
 
 The brother smiled at the simplicity of the re- 
 quest ; but, to let the girl see the result of en- 
 larging the light-hole, he set to work to make a 
 greater aperture in the front of the box. This 
 done, he told Kitty once more to peep through the 
 hole in the lid. 
 
 4 4 Why, what’s the matter with it, Humphry?” 
 cried the sister ; 44 1 don’t see anything at all 
 now.” 
 
 Humphry smiled at his sister’s wonder, and pro- 
 ceeded to recount to her the reason why the pic- 
 ture had become obliterated. He told her that 
 when the hole was a very small one, no two rays 
 from different parts of the object fell upon the same 
 place ; but that, now the hole was enlarged, the 
 rays that were being sent off in all directions from 
 every part of the rose-tree became confused with 
 one another, so that those from the green leaves 
 fell upon the same part of the paper as those from 
 the red flowers, and the consequence was that the 
 one colour obliterated the other. 
 
 For the easier comprehension of this part of the 
 
S46 
 
 THE WONDERS OF SCIENCE. 
 
 subject, Humphry drew the subjoined representa- 
 tion of the rays proceeding from one of the flowers 
 
 and one of the leaves ; where it will be seen that, 
 owing to the enlargement of the aperture at the 
 front of the box, the red ray from the flower, 
 and the green ray from the leaf, fall upon the 
 same part of the paper at the back ; for as the 
 leaf and the blossom each send off rays in all direc- 
 tions, it is evident that — supposing only two of 
 these, for simplification sake, to pass through the 
 aperture — one of the green leaf-rays would fall 
 upon the same spot with one of the red blossom- 
 rays, and one of the blossom-rays, on the other 
 hand, become blended with one of the leaf-rays. 
 
 Kitty was not a little disappointed at the result 
 which had followed the enlargement of the light- 
 hole ; but Humphry, to console her, said that it 
 was possible, by means of a lens, to increase the 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 847 
 
 light, and yet to prevent the rays from different 
 points of the object falling upon the same part of 
 the paper at the end of the box. 
 
 For this purpose the lad placed a double con- 
 vex lens, which he had previously made out of two 
 watch-glasses cemented together, into the aperture 
 at the front of the cigar-box, and then told his 
 sister to look once more through the hole in the 
 lid. 
 
 Kitty no sooner applied her eye to the sight- 
 hole than she cried aloud, “ O how beautiful ! I 
 declare it is much brighter than the first, and I 
 can now see every leaf and blossom perfectly made 
 out. It’s the picture of a little fairy rose, — that it 
 is. But tell me, Humphry,” said the girl, “ how 
 could a little bit of rounded glass like that which 
 you put into the box produce so wonderful a 
 change ?” 
 
 “Well,” returned the brother, “you recollect I 
 told you that every object which we see is sending 
 off rays of light from every part of it in all direc- 
 tions. In the first case, when there was a mere 
 pin-hole in front of the box, the aperture was so 
 small that only one ray from each point of the 
 rose-tree passed through it, and, therefore, the 
 image was so dim you could scarcely make it out. 
 With the convex lens, however, as many more rays 
 enter the box from every part of the plant, as the 
 lens itself is bigger than the small hole which 
 
348 
 
 THE WONDERS OF SCIENCE. 
 
 we had in the box at first ; and the reason, again 
 why these rays are prevented from becoming con- 
 fused one with the other, and so obliterating the 
 picture — as was the case when we enlarged the 
 light-hole in front of the box, without inserting 
 any lens in it — is because they are all duly re- 
 fracted by the lens, so that they severally fall in 
 their proper places. But you will understand 
 this better by a drawing.” And, so saying, Hum- 
 phry prepared the illustration below given: — 
 
 “ Here you see there are three rays,” continued 
 the lad, “ drawn from the top, bottom, and centre 
 of the object ; three only are given for the sake 
 of simplicity, though every point of the plant is 
 sending light from it in the same manner as here 
 indicated. Well, Kitty, the rays from the flower 
 at the top of the tree fall upon every part of the 
 glass, and, by the laws of refraction, are made to 
 come together at a point on the other side of it. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 349 
 
 Again, the rays from the leaves at the bottom of 
 the tree fall upon every part of the lens, and are so 
 refracted that they all meet at another point on the 
 other side of the glass ; while those from the rose- 
 bud in the centre are likewise blended into a focus 
 at the same distance behind the lens. But you 
 will perceive, that the rays which come from the 
 upper part of the object fall at the lower part of 
 the image ; and those, on the other hand, which 
 proceed from the top, fall at the bottom. This is 
 because the rays from these parts cross one another 
 in the centre of the lens, while those which are sent 
 off from the rosebud in the middle suffer no change 
 of position, because they proceed — as you observe 
 by the dotted lines in the drawing — directly 
 through the glass, rather than traversing it ob- 
 liquely as the others do.” 
 
 “ Oh, thank you, Humphry,” said Kitty ; “ I can 
 make it out well now. The image from the lens is 
 so much brighter because it not only allows more 
 light to pass through the aperture, but prevents 
 the rays from the different parts of the object 
 mingling one with the other. But, Humphry,” 
 ejaculated the girl, as a new thought struck her, 
 “the image, as you call it, is much smaller than 
 the rose-tree itself : why is that ?” 
 
 “ To make you understand this, Kitty,” answered 
 the boy, “ I will place the tree farther from the 
 lens, and you shall tell me the effect.” 
 
350 
 
 THE WONDERS OF SCIENCE. 
 
 Humphry had no sooner removed the plant to a 
 greater distance, than the girl cried, “ Oh, it’s 
 much smaller than ever now!” 
 
 “ And now that I bring it nearer the box what 
 do you see ?” inquired the youth. 
 
 “Why it seems to grow and grow, Humphry,” 
 replied Kitty, as she continued peeping through 
 the hole in the lid, “ so that I fancy it would get 
 as big as the tree itself. The picture, though, is 
 not nearly so bright.” 
 
 “No,” returned her brother ; “that is because it 
 gets out of focus. Now look you here, Kitty ; I 
 will do another drawing, to enable you to compre- 
 hend how the size of the image depends upon the 
 distance of the object from the lens. 
 
 “ You must bear in mind,” proceeded Humphry, 
 on the completion of the diagram, “ that the rays 
 which pass through the centre of a lens never 
 change their direction . Well, I have drawn here, 
 you see, one ray from the tip of the arrow, and one 
 from the bottom ; and as these rays necessarily 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 351 
 
 form the extremes of the image, and so regulate its 
 size, you will readily comprehend that, when the 
 object is, as here represented, 4 yards, or feet, — or, 
 indeed, 4 measures of any kind — in front of the 
 lens, and the image falls, also, at 4 such measures 
 behind it, as at the arrow 4, the image itself must 
 be exactly of the same size as the object. If, how- 
 ever, the image fell at half the distance behind the 
 lens which the object was from the front of it, then 
 the picture would be only half the size of the body 
 producing it, — as here, at the arrow 2 ; whereas if 
 the image was at twice the distance of the object 
 from the lens, as at the arrow 8, then it would be 
 exactly twice the size of it. Consequently, the 
 dimensions of the image produced by a lens bear 
 always the same proportion to the object as the 
 distance of the object from the lens does to that of 
 the image: that is to say, if the object be 3 times 
 as far from the lens as the image is, then the image 
 will be 3 times smaller than the object itself, and 
 vice versa , if the object be 3 times nearer the lens 
 than the image, then the image will be 3 times 
 larger than the object.” 
 
 Kitty having informed her brother that she 
 thoroughly understood the matter now, Humphry 
 went on to tell her that, in order to produce an 
 image, it was necessary that the picture should be 
 received upon some opaque or in transparent sub- 
 stance, otherwise the rays of light would pass 
 
852 
 
 THE WONDERS OF SCIENCE. 
 
 through the substance itself without being reflected 
 from it or sent back to the eye. 
 
 “ The opaque body,” continued the youth, “ upon 
 which the image is thrown, should be of a white 
 colour, for this reflects the greatest amount of 
 light” 
 
 To elucidate this part of the subject, Humphry 
 removed the wooden end of the cigar-box that he 
 had previously employed, and substituted a piece 
 of ground glass in its stead ; when Kitty, on 
 placing her eye behind the box, saw the picture of 
 the rose-tree once more portrayed upon it. 
 
 “Now,” added her brother, “if I smear the 
 ground glass over with any grease, or even water, 
 so as to increase its transparency, you will see that 
 the image immediately disappears.” 
 
 This done, Humphry explained to Kitty that 
 the image might be received upon smoke, or, indeed, 
 any vapour that consisted of a number of opaque 
 white particles, and then he recounted to her the 
 story of the “ spectre of the Brocken.” 
 
 “ The Brocken,” said he, “ is the name given to 
 the loftiest of the Hartz mountains, which is a pic- 
 turesque chain of hills situate in the kingdom of 
 Hanover. The highest of these is elevated 3300 
 feet above the sea, and commands the view of a plain 
 upwards of 200 miles in extent. This spot has been 
 the seat of the marvellous from the earliest periods. 
 One of the accounts given of the 6 Spectre of the 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 353 
 
 Brocken’ is that of M. Haue. After having been 
 on the summit of the mountain no less than thirty- 
 times, he had, at last, the good fortune of witness- 
 ing the object of his curiosity. The sun rose at 
 about 4 o’clock in the morning, through a serene 
 atmosphere. In the south-west, towards Achter- 
 mannshohe, a brisk wind carried before it the 
 transparent vapours which had not yet been con- 
 densed into thick, heavy clouds. About a quarter 
 past 4 M. Haue looked round to see whether the 
 atmosphere would afford him a free prospect to- 
 wards the south-west, when he observed, at a very 
 great distance towards Achtermannshohe, a human 
 figure, of a monstrous size. At this moment a 
 violent gust of wind ensued, and M. Haue sud- 
 denly raised his hand to his head, to prevent his 
 hat being carried away, when, to his great asto- 
 nishment, he beheld the colossal figure in the dis- 
 tance do the same. He immediately made another 
 movement by bending his body, and this action, 
 too, was instantly repeated by the spectral figure. 
 There was now no doubt that what was termed the 
 6 Spectre of the Brocken ’ was an enormous image 
 of the spectator himself seen in the distance. M. 
 Haue was desirous of making other experiments, 
 but the figure disappeared. He remained, how- 
 ever, in the same position, expecting its return ; 
 and in a few minutes it again made its appearance 
 on the Achtermannshohe, when it once more 
 
 A A 
 
354 
 
 THE WONDERS OF SCIENCE. 
 
 mimicked his gestures as before. M. Haue then 
 called another person to him, and having both 
 taken the same position which he himself had pre- 
 viously occupied, they looked towards the Achter- 
 mannshohe, but saw* nothing. In a very short 
 space of time, however, two colossal figures were 
 formed above the eminence, and, after bending 
 their bodies, and imitating the gestures of the spec- 
 tators, they disappeared. M. Haue and his com- 
 panion, nevertheless, retained their position, and 
 kept their eyes still fixed upon the same spot, when 
 the two gigantic spectres were again beheld by 
 them, but this time they were joined by a third, 
 
 and, strange to say, every movement they made 
 was imitated by all the three figures . The effect, 
 however, varied in its intensity, being sometimes 
 weak and faint, and sometimes strong and well- 
 defined. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 355 
 
 “ These figures were merely shadows of the ob- 
 servers, projected on dense vapour, or thin fleecy 
 clouds, which have the power of reflecting much 
 light. They are seen most frequently at sunrise, 
 because at that time the vapours and clouds neces- 
 sary for their production are usually generated ; 
 and they can be perceived only when the sun is 
 throwing his beams horizontally, because the shadow 
 of the observer would be otherwise projected up in 
 the air, or down upon the ground. It is very pro- 
 bable that the third figure observed by M. Haue 
 was formed by a duplication of one of the others, 
 produced by unequal refraction ; though M. Haue 
 himself does not state which of the two figures was 
 doubled.” 
 
 It may here be added, that another story of the 
 same kind is told by Sir David Brewster. “A 
 young lady had ascended to the top of the Mynydd, 
 a steep hill, about 500 feet above the valley of 
 New Badnor, in South Wales. The sun was 
 bright and hot (it being about 2 o’clock in the 
 day). Having picked some flowers on the top of 
 the hill, the girl descended a little way, to a spot 
 from which she could see the road and the carriage 
 with her companions whom she had left in it below. 
 After waving the scarf which she held in her hand 
 to her friends, she suddenly perceived, upon turn- 
 ing round, a figure standing a few yards from her 
 
356 
 
 THE WONDERS OF SCIENCE. 
 
 upon a wet spot, from which a little thin mist was 
 rising . The figure stood exactly facing her, and 
 wavered a little ; but she did not discover it to 
 be her own image, till she observed that, like her- 
 self, it held a scarf and a bunch of flowers in one 
 hand. The dress and flowers were precisely simi- 
 lar to her own, and the colours so vivid that she 
 could even trace her own features in the image. 
 The effect was the same as if she had been before a 
 looking-glass — when she moved her hand, the 
 figure did the same. The two friends in the car- 
 riage saw the image of the young lady, and asked 
 her, when she joined them, what companion she 
 had had on the hill. There can be no doubt,” adds 
 Sir David Brewster, “that the figure was a re- 
 flexion of the young lady, produced by the thin 
 mist rising from the damp ground ; for it may be 
 proved, by experiment, that when the particles of 
 vapour are sufficiently small, they reflect light as 
 distinctly as a surface of glass.” 
 
 From the production of images, Humphry passed 
 to the consideration of the circumstances by which 
 lenses appear to increase the size of objects , and so 
 to make them seem as if brought nearer to us . 
 
 “ When a shilling,” said Humphry, “ is at the 
 distance of 6 or 8 inches from the eye, we can 
 read the inscription round it with perfect distinct- 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 357 
 
 ness. At the distance of 3 yards, however, we 
 can no longer make out the inscription, but see 
 only the king’s head upon it. Again, at the dis- 
 tance of only 20 or 30 yards, we lose sight of the 
 head, and can then just distinguish that it is a 
 round body ; whilst, when placed at about 100 
 yards from us, the coin is scarcely visible. The 
 reason of this is, that the shilling decreases in size 
 the farther it is removed from us, for we then see 
 it under a smaller angle , as it is termed ; and it is 
 found that the smallest angle under which an 
 object can be seen, is, upon an average for dif- 
 ferent sights, the 60th part of a degree, or one 
 minute in space ; so that when an object is re- 
 moved from the eye about 3000 times its own 
 diameter, it will only just be distinguishable. Con- 
 sequently, the greatest distance at which we can 
 behold an object like a shilling, of an inch in dia- 
 meter, is 3000 inches, or 250 feet. 
 
 “ Another drawing,” added Humphry, “will 
 enable you, Kitty, readily to comprehend how an 
 object appears to diminish in size, according as 
 
 it becomes more and more distant from us. and so 
 gets to be seen under a smaller angle.” 
 
358 
 
 THE WONDERS OF SCIENCE. 
 
 “ There,” continued the boy, “ the first arrow is 
 seen under an angle of 120°,* whereas the angle 
 under which the second arrow is regarded is only 
 60°. Consequently, though the objects are the 
 same in size, the one will appear only \ the length 
 of the other. The third arrow, again, being seen 
 under an angle 4 times smaller, will seem to be 
 only Jth the size of the first ; whilst the fourth 
 arrow, for the same reason, will look as if it were 
 only £th the height of the one next the eye ; and 
 the farthest arrow of all but T ^th as large as the 
 nearest. Moreover, if we suppose another arrow 
 still to be so far removed that the angle under 
 which it is seen dwindles down to the 60th part of 
 a degree, or T, as it is called, this will then appear 
 so reduced in size as to be only just distinguish- 
 able to us. 
 
 “ Well, Kitty,” the youth went on, “ you now 
 understand that an object appears to diminish in 
 size the farther it is removed from us, merely 
 because it is seen under a lesser angle ; and, conse- 
 quently, an object must seem to us, on the other 
 hand, to increase in size when the image of it is 
 brought nearer to the eye, and so gets to be 
 
 * The range of the eye, or diameter of the field of vision, is 
 110° ; consequently, this is the largest angle under which an ob- 
 ject can be seen. The largest angle, however, is here made 120% 
 for the simplification of the numbers. The range of vision is from _ 
 110° to 1% 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 359 
 
 viewed under a greater angle. This, then, is all 
 that lenses really do when they appear to magnify 
 objects : that is to say, they do not absolutely 
 increase the dimensions of the bodies under view, 
 but merely bring tlieir images nearer to the eye, 
 and so enable us to see them under a larger angle . 
 You remember I told you that, with a shilling, we 
 can just see the king’s head upon it at the distance 
 of about 10 feet from the eye. Now, when the 
 coin is at that distance, if a convex lens, having a 
 focus 2J feet long, be placed midway between the 
 shilling and the eye, the lens will, of course, be 5 
 feet from the eye and 5 feet from the shilling ; so 
 that, in this case, it is plain, from what I before 
 explained to you about the size of images,* that 
 the image of the shilling seen behind the lens will 
 be exactly of the same dimensions as the shilling 
 itself in front of it. The object, therefore, will 
 not have been directly magnified by the lens. The 
 image, however, will be thus brought so near to 
 the eye, that the coin may be seen by us at the 
 distance of 6 inches, instead of 10 feet ; and, con- 
 sequently, being viewed under a proportionately 
 larger angle, the shilling will seem to be magnified 
 as many times as 10 feet is greater than 6 inches ; 
 or, in other words, it will be made to appear 20 
 times larger in our eyes. Hence the shilling will 
 have been, apparently, magnified 20 times, merely 
 * See illustration at p. 350. 
 
360 
 
 THE WONDERS OF SCIENCE. 
 
 by bringing the image of it 20 times nearer the 
 eye, — thus. Whereupon the boy proceeded to de- 
 lineate the following diagram ; in which the dotted 
 
 c D 
 
 lines from the object A represent the angle that the 
 shilling itself would be viewed under without the 
 lens, C, by the eye at B, while the dotted lines from 
 the image D show the much larger angle that such 
 image would be seen under with the lens. 
 
 Humphry then prepared an experiment illustra- 
 tive of the apparent magnifying of objects by lenses, 
 when their images are brought nearer to the eye. 
 For this purpose he got Kitty to bore a hole in the 
 shutter large enough to allow a lens to be inserted 
 in it. Then fixing the glass in the aperture, he 
 bade his sister close the shutters, and place her 
 eye at about feet from the lens, for such he 
 knew to be the length of its focus. 
 
 “ How beautiful ! ” cried the girl, as she gazed 
 through the transparent circle. “I see a tiny 
 image of Madern Church ; and so close, too, that I 
 could fancy it was in the room here.” 
 
 “ Well,” said Humphry, “ the church itself, you 
 know, is about \\ mile distant, or, let us say, 7500 
 feet, and the focus of the lens is feet ; conse- 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 861 
 
 quently it follows, from what I have before told 
 you, that the image of the church you see is 3000 
 times smaller than the church itself, for 0 = 
 3000. Nevertheless, if we could copy the image 
 of the church upon a piece of paper, — or, what 
 would be better still, fix it upon a sheet of glass, 
 we should find that, on holding it just as far from 
 the eye as it is now from the lens , the tiny image 
 that you now see would exactly cover every part of 
 the distant object, and so appear precisely of the 
 same size as the church itself, — in this manner. 
 
 A 
 
 “ Let us suppose the large dart, marked A here,” 
 the lad continued, as he drew the plan upon paper, 
 “to be the height of the church, and the smaller 
 dart, a, on the other side of the lens, C, to be the size 
 of the image that we see. Well, if you were to place 
 your eye where the lens now is, and the image just 
 as far in front of the glass as it now stands behind 
 it , it is plain, by the dotted eye and arrow at a , that 
 the one would exactly cover the other. 
 
 “Hence it is evident,” added Humphry, “ that 
 the image which you see behind the lens is really 
 
362 
 
 THE WONDERS OF SCIENCE. 
 
 of the same size as the distant object appears to 
 be, even though, as in the case of Madern Church, 
 the image is no less than 3000 times smaller than the 
 object itself really is. But when you look through a 
 glass, Kitty, the image of the distant object is only 
 about 6 inches from your eye ; so that, though it is 
 of the same size as the object itself appears to be, 
 you are viewing it at a shorter distance than the 
 length of the focus of the lens ; and, therefore, 
 owing to your regarding it under a greater angle, 
 it seems to be magnified. Now, as I told you, the 
 focus of the lens we employed was 2J feet, or 30 
 inches long ; and, supposing your eye to have been 
 where the lens was, and the image transferred to 
 the other side of the lens (as indicated by the dotted 
 eye and arrow marked a '), the image would have 
 seemed exactly the same size as the object itself, 
 provided it had been placed at a distance of 30 inches 
 in front of you. If, however, the image had been 
 placed only 6 inches away from your eye, it is 
 plain that you would have been viewing it 5 
 times closer than feet, and this would be the 
 same as if the dotted arrow had been shifted from 
 a to x ; consequently, it would then have looked 
 to you 5 times larger than it really was, because 
 you were regarding it under an angle 5 times 
 greater than its own. 
 
 “The result which we come to is, therefore,” 
 concluded the youth, “ that the magnifying power 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 363 
 
 of a lens is always equal to its focal length , divided 
 by the distance at which the eye regards the image . 
 The latter, in jour case, Kitty, was about 6 inches ; 
 so that the lens, having its focus 30 inches off, the 
 magnifying power of it is arrived at in this manner : 
 
 V=s. 
 
 Kitty asked whether it was possible to magnify 
 an object any more than that ; when Humphry 
 told her that, had the focus of the lens he em- 
 ployed been longer, its magnifying power would 
 have been greater ; “ as for instance,” said he, 
 “ if the length of the focus had been 5 feet, instead 
 of 2 J, it would have magnified 10 times instead of 
 only 5, for 6 6 ° -^^ =10. So, again, had the focus 
 of the lens been 10 feet, its magnifying power 
 would have been doubled again, for^|^^=20. 
 But,” continued the boy, “the magnifying power 
 might be increased in another way, — namely, by 
 bringing the eye nearer to the image. As yet we 
 have estimated the distance at which the eye views 
 the image produced by the lens at 6 inches, be- 
 cause that is the length at which we see near 
 objects distinctly. Hold your finger before your 
 eye, Kitty, and you will see that when you bring it 
 very close you can scarcely distinguish it. With 
 a lens, however, having a short focus, you would 
 be able to see the finger much nearer than natu- 
 rally ; and then, for the reason I have before given 
 you, it would appear to be as much magnified as 
 
364 
 
 THE WONDERS OF SCIENCE. 
 
 the distance at which you beheld it distinctly 
 with the lens was less than 6 inches, which is 
 the distance at which you beheld it distinctly 
 without the lens. In my cupboard you will find 
 a burning-glass, and that has a focus of only 2 
 inches. Do you get it, Kitty, and look at your 
 finger through it.” 
 
 The girl did as she was bidden, and immediately 
 cried, “ Oh, Humphry ! what a horribly ugly, 
 coarse, thick-looking thing it is ! Why, I declare 
 my skin looks like an elephant’s hide through it ; 
 and I can see every line in it, like the veins on a 
 leaf!” 
 
 “Yes,” returned her brother, “that is because 
 you are now looking at your finger 3 times nearer 
 than you could see it distinctly without the lens, 
 and, consequently, you behold it under a propor- 
 tionately larger angle ; so that it appears to you to 
 be 3 times magnified — for yj^i=3. Let us then 
 apply the same principle to the image of Madern 
 Church as seen through the lens in the shutter, 
 and which, you remember, appeared to be magni- 
 fied 5 times, because you saw it at 6 inches from 
 your eye instead of 30 inches, which was the focal 
 length of the lens. But now, by means of this 
 burning-glass held near your eye, do you look at 
 the image once more, and tell me, Kitty, what 
 you see.” 
 
 The shutters were accordingly closed again, 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 365 
 
 and the girl proceeded to take another peep at the 
 distant church through the two lenses. 
 
 “ Oh, Humphry ! ” she cried, “ I see it much 
 plainer than ever ; and it is, as you say, a great 
 deal bigger, too.” 
 
 “ Of course it is,” returned the brother, “ for the 
 length of the focus of the burning-glass is, as I 
 said, 2 inches ; so that you now see the image of 
 the church at that distance from your eye, instead 
 of 6 inches, as before. The image, therefore, ap- 
 pears to be magnified 5 times by the first lens, and 
 3 times by the second, or 5x3 = 15 times in all ; 
 and the reason of its appearing to be that number 
 of times larger to you, is simply because you are 
 looking at it at 15 times a shorter distance than the 
 focal length of the lens in the shutter, which is 
 called the 6 object-glass,’ and so seeing it by means 
 of the other lens, which is called the ‘ eye-glass,’ 
 under 15 times a greater angle than you behold the 
 object itself with your naked eye .” 
 
 “ I understand it now perfectly, Humphry, thank 
 you,” said the sister, pleased with the explanation. 
 “ And are the telescopes that the sailors use made 
 upon the same^ principle ?” 
 
 “ Precisely so, Kitty,” responded the brother. 
 “ And in order to find out the magnifying power of 
 any of these, we have merely to divide the length 
 of the focus of the object-glass by that of the eye- 
 glass *, and the quotient will tell us how many 
 
306 
 
 THE WONDERS OF SCIENCE. 
 
 times the objects are enlarged by them ; whilst in 
 order to make a telescope for ourselves, we have 
 merely to procure a lens of a long focus — say 12 
 inches, and one of a short focus — say 2 inches, 
 and then to set these in a tube at the length of the 
 two foci, or 12 + 2 = 14 inches apart. This tube, 
 however, should be a sliding one, so as to admit of 
 the distance between the two lenses being in- 
 creased according as the objects viewed are nearer 
 at hand ; for I told you before, you remember, 
 that the nearer the object the farther is the image 
 from the lens, and vice versa , the more distant 
 the object, the shorter the focus of the glass be- 
 comes.”* 
 
 * The arrangement of lenses, above described, constitutes the 
 principle of what is termed the “ astronomical telescope for this 
 makes the objects appear upside down. But, though the inver- 
 sion of a star or planet is a matter of no moment in astronomical 
 observation, such an effect is most disagreeable when applied to 
 terrestrial objects. The ordinary telescope for land purposes, 
 therefore, — or the 11 day telescope,” as it is usually styled, — has 
 two other lenses behind the eye -lens. These lenses have both 
 the same focus as the eye -lens itself, and are placed at a fixed 
 distance from each other, such distance being equal to the sum of 
 their focal lengths : that is to say, if the eye-lens have a focus 
 of 2 inches, then each of the two other glasses should have the 
 same length of focus, and be placed at 4 (2 + 2) inches apart from 
 one another. The magnifying power of the day telescope may be 
 calculated in the same manner as that of the astronomical one 
 above explained ; for the two additional lenses in the day instru- 
 ments, having the same focal length as the eye-lens itself, pro- 
 duce no further enlargement of the objects, but serve only to ~ 
 cross the rays a second time, and so to render the image erect 
 instead of inverted . 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 367 
 
 Now that Kitty understood the principle upon 
 which telescopes were constructed, she begged her 
 brother to promise to construct one as soon as he 
 was well ; and Humphry haying consented, the 
 two then passed on to the consideration of the prin- 
 ciple of the microscope. 
 
 “ I have already told you,” said Humphry, on en- 
 tering upon the subject, “that the nearer an object 
 comes to us, the larger it appears. But, as you 
 saw, when you held your finger close before your 
 eye, it grew so indistinct and confused, that the 
 form of it was almost as obscure as if it had been 
 at a great distance from you. Now this effect is 
 produced by the greater divergence of the rays of 
 light, whenever an object is brought nearer to 
 us ; and when the divergence is very great, the 
 crystalline lens within the eye has not power to 
 collect the rays into a focus on the retina at the 
 back of the eyeball. You will understand how the 
 rays come to diverge more and more the nearer 
 an object approaches to 
 us, by the following illus- 
 tration. 
 
 “ There, we will suppose 
 the eye to be looking at 
 some very minute object, 
 like a speck of the dust from a butterfly’s wing, at 
 the distance of 6 inches, 4 inches, and 2 inches. 
 Well, at 6 inches, the rays of light given off by it, 
 
 
368 
 
 THE WONDERS OF SCIENCE. 
 
 you perceive, diverge but slightly in comparison 
 with the angle at which they enter the eye at 2 
 inches. Consequently, the image produced within 
 the eye itself would, in the latter case, be so dim 
 that we should be almost unable to distinguish it. 
 In order, however, to look at a very small object, 
 we must bring it as close as possible to the eye ; 
 so that, to enable us to see it distinctly at a short 
 distance, we must find out some means of de- 
 creasing the divergence of the rays of light from 
 near objects, — or, what would be better still, 
 of making the rays enter the pupil in parallel 
 lines. 
 
 Now I showed you, a short while back, that a 
 convex lens causes the rays of light from objects 
 placed in its focus to pass out on the other side of 
 the glass parallel to each other. Consequently you 
 perceive that, by means of a double convex glass, we 
 can see objects distinctly when held at \ an inch — 
 or even the -^th of an inch — from our eye, pro- 
 vided such be the focal length of the lens em- 
 ployed ; and thus we shall, for the reasons before 
 explained, obtain a magnifying power which will he 
 equal to the distance at which the naked eye can 
 see minute objects distinctly divided by the focal 
 length of the lens employed . For example, the 
 
 distance of distinct vision for very minute objects 
 may be taken at 5 inches, so that if we make use 
 of a lens having a focus of 1 inch, the magnifying 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 809 
 
 power will be equal to 5 inches divided by 1 ; 
 that is to say, an object viewed with such a glass 
 will appear to have its length and breadth in- 
 creased five -fold ; so that its length being magni- 
 fied 5 times, and its breadth 5 times also, its 
 entire surface will be increased as much as 25 
 times, or 5x5. If, however, we employ a lens 
 having a focus of only ^th of an inch, the linear 
 magnifying power will be equal to 5 inches divided 
 by xgth (or Ail), that is to say, to 50-fold ; while 
 the superficial magnifying power will amount to 
 50 x 50, or 2500-fold ; and if, again,” went on the 
 lad, “ the lens employed have a focus of only T q- ^ th 
 of an inch, then the linear magnifying power will 
 be equal to 5 inches divided by yj^th (or AAA), 
 — that is to say, to 500, and the superficial magni- 
 fying power to 500 x 500, or 250,000. 
 
 “ A lens of a very short focus,” added Humphry, 
 constitutes what is termed the single microscope. 
 For this purpose the lens is usually made spherical, 
 — as a sphere, or round ball of glass, has its focus 
 at a distance from its centre equal to 1| its own 
 radius; so that if we had a small glass ball, of 1 
 inch in diameter, the focus of such a lens would 
 fall at -J of an inch from the centre of the ball 
 itself ; whereas if the ball was -ith of an inch in 
 diameter, it would have the focus at T 3 gths of an 
 inch from its centre : so that you will readily com- 
 prehend, Kitty, how tiny a sphere must be used 
 
 B B 
 
370 
 
 THE WONDERS OF SCIENCE. 
 
 in order to give great magnifying power with a 
 single microscope. To have a lens of ^th of an 
 inch focus that will, consequently, be able to mag- 
 nify an object 50 times in length and breadth, 
 it would require the glass sphere to be only about 
 -J^ths of an inch in diameter. The perfect execu- 
 tion of such lenses requires considerable skill in 
 the grinding and polishing, therefore other means of 
 constructing them have been desired. One simple 
 method of forming a microscopic lens consists in 
 drawing out (by means of a spirit-lamp) a thin strip 
 of window-glass into threads, and holding the end 
 of one of such threads in the flame until it runs 
 into a globule. The globule is then cut off and 
 set in a small aperture, in such a manner that none 
 of the rays may pass through that part of the tiny 
 ball where it was originally united to the thread. 
 Another process,” continued the youth, “ consists in 
 taking up some fine-pounded glass on the wetted 
 point of a needle, and then melting it by a spirit- 
 lamp into a globule, after which the globule is re- 
 moved, and once more taken up, by the wetted point 
 of the needle, on its round side, when it is again 
 inserted in the flame, until it becomes a perfect 
 sphere. Moreover, drops of water, as well as 
 drops of oil or varnish, have been used for micro- 
 scopic lenses. These are placed on a small piece 
 of plate glass, and have considerable magnifying 
 powers. Further, the lenses from the eyes of fish 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 371 
 
 have been used for the same purpose ; but, in this 
 case, it is necessary to look through the lens in 
 the direction of its axis — or, in other words, in the 
 same manner as the fish did.* 
 
 “ A good extempore microscope may be formed 
 out of two test-tubes filled with water, and placed 
 one across the other, like the algebraic sign +.” 
 
 To please his sister, Humphry had his spirit- 
 lamp lighted, and proceeded to form some little 
 globules of glass in the flame, in the manner be- 
 fore explained ; and then, having set these upon 
 a plate of brass, he showed the delighted girl how 
 wonderfully objects were magnified by them ; and 
 afterwards he went on to explain to her how it was 
 
 * Within the last 30 years the diamond has been used for 
 the purpose of microscopic lenses ; for, owing to the refractive 
 power of this precious stone being greater than almost any other 
 known substance, and nearly double that of glass, lenses can be 
 produced from it of a great degree of magnifying power, and that 
 with a comparatively small curvature, so that increased distinct- 
 ness is obtained ; while the lens itself, being nearly “ achromatic ,” 
 the image produced by it is untinged by prismatic colours. Mr. 
 Pritchard constructed the first diamond microscope in 1826. The 
 diamond lens of this was double convex, and had a focus of ggth 
 of an inch, so that its magnifying power was 150 times. Dr. 
 Goring, an eminent authority on the subject, says, — “ I conceive 
 diamond lenses to constitute the ultimatum of perfection in the 
 single microscope.” The sapphire has also been used for the 
 construction of microscopic lenses with considerable advantage, 
 its magnifying power being much greater than that of glass. 
 Mr. Pritchard says, that the sapphire, next to the diamond, 
 possesses all qualities requisite for the formation of a perfect 
 magnifier, and presents less difficulties in the construction. 
 

 3^2 THE WONDERS OF SCIENCE. 
 
 possible to increase the microscopic power of lenses, 
 even without diminishing their size. 
 
 “ Suppose,” said he, “ that we have a lens of 
 ^ an inch focus, and which would, therefore, mag- 
 nify the diameter of objects 10 times; and then 
 suppose that, instead of looking directly at the 
 image, we place another lens of a short focus — say 
 1 inch — between it and our eye, and so view the 
 image through the second lens. Well, this second 
 lens would, for the reasons before given, magnify 
 the object 5 times more ; so that it would thus be 
 made to appear 50 times bigger in all, the image 
 being rendered 10 times greater by the first lens, 
 and that image, again, 5 times greater by the 
 second. This constitutes what is termed the com- 
 pound microscope ; and, by means of this instrument, 
 objects may be magnified almost to any extent.” 
 
 Humphry having now thoroughly made out to 
 himself, as well as his sister, the principle upon 
 which the powers of the microscope and telescope 
 depends, concluded the subject by drawing the 
 following diagrams, illustrative of the opposite action 
 of the two instruments : — 
 
 Telescopic arrangement. 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 373 
 
 Microscopic arrangement. 
 
 “ There,” said the boy, “ in the one case, as in the 
 preceding diagram, the object is at a considerable 
 distance from the lens, and the image near it ; 
 while in the other, as in the above diagram, the 
 object is near the lens, and the image at a con- 
 siderable distance from it. Now if we suppose, 
 Kitty, the object to be 10,000 feet in front of the 
 first lens, and the image 10 feet behind it, it fol- 
 lows that the image, in this case, would be 1000 
 times smaller than the object itself ; and if we 
 suppose, on the other hand, the object to be Too^ 
 of an inch in front of the second lens, and the 
 image to be 10 inches behind it, then the image, in 
 that case, would be 1000 times larger than the 
 object itself. Let us now imagine another lens to 
 
 Astronomical Telescope. 
 
 be placed before each of the images — as here 
 shown — so that the eye may view them at a 
 
374 
 
 THE WONDERS OF SCIENCE. 
 
 shorter distance than it could see them distinctly 
 without any such aid ; and let us say, again, that 
 the focal length of this second lens is, in both cases, 
 1 inch. Well, then, we should be regarding the 
 image in the upper diagram at a distance of 1 inch 
 instead of 10 feet, which is the focal length of the 
 object-glass, and so bringing it 100 times nearer to 
 our eye ; the consequence would be, that it would 
 appear to us to be 100 times larger than it would 
 at the distance of 10,000 feet, so that this would 
 be the magnifying power of the instrument, which, 
 as I said before, is always equal to the focal 
 length of the object-glass , divided by that of the 
 eye-glass . Such, then, constitutes the arrange- 
 ment of the astronomical telescope. In the com- 
 pound microscope, however,” added Humphry, 
 “ the magnifying power is estimated by multiply- 
 ing instead of dividing the power of the object- 
 glass by that of the eye-glass ; so that, as we sup- 
 posed the first lens in the lower diagram to mag- 
 nify the object 1000 times, and the second lens 
 now enables us to view the image distinctly 
 at 5 times nearer the eye than we could with- 
 out it, the gross magnifying power, therefore, 
 must amount to no less than 1000 x 5, or 5000 
 times.” 
 
 The youth then went on to explain to his sister 
 that the same relation which exists between the 
 telescope and the microscope, also holds good be- 
 
THE WONDERS OF THE REFRACTION OF LIGHT. 375 
 
 tween the camera-obscura and the magic -lantern. 
 In the camera-obscura, for instance, the object, as 
 in the telescope, is at a considerable distance in 
 front of the object-glass, and the image at a short 
 distance behind it ; whereas in the magic-lantern, 
 the object, as in the microscope, is at a short dis- 
 tance in front of the object-glass, and the image at 
 a considerable distance behind it. In the camera, 
 therefore, the image is as much diminished as 
 it is nearer the lens than the object ; whilst 
 in the magic-lantern the image is as much mag- 
 nified as it is farther from the lens than the 
 object. 
 
 The annexed drawing will illustrate the action 
 of these two instruments clearer than words can 
 describe them : — 
 
 The reader has only to suppose the image pro- 
 
376 
 
 THE WONDERS OF SCIENCE. 
 
 duced by the camera — a portrait, let us say — to be 
 fixed upon glass (by the “ collodion process” of 
 photography, an invention since Davy’s time), and 
 this image to be made to serve as the object (or, 
 in plainer language, the slide) of the magic-lan- 
 tern, in order to comprehend how the object in the 
 one instrument may be made the image in the other, 
 and vice versa , the image of the first the object of 
 the second. 
 
THE WONDERS OF THE REFLEXION OF LIGHT. 377 
 
 CHAPTER XVI. 
 
 THE WONDERS OF THE REFLEXION OF LIGHT. 
 
 Hitherto Humphry had considered only the laws 
 which regulate the transmission of light through 
 transparent bodies. This constitutes the branch 
 of the subject called dioptrics (from through, 
 and oKTopui, to see). The other branch, termed 
 catoptrics (from from, or against, and onropcu, 
 to see), deals with the laws of light when it is 
 reflected or thrown back from the surface of any 
 body against which it falls. Accordingly the lad 
 passed, in due order, from the transmission to the 
 reflexion of the luminous rays. 
 
 To explain this part of the subject the youth 
 first procured a piece of an old looking-glass, and 
 having got Kitty to close the shutters once more, 
 he placed the looking-glass upon the ground, so 
 
378 
 
 THE WONDERS OF SCIENCE. 
 
 that the ray might fall just in the middle of it ; 
 when, as the room was thoroughly darkened, it was 
 easy to observe the inclination, or angle, at which 
 the light fell on the reflector, as well as to perceive 
 the course it took afterwards. 
 
 “ Why, I declare,” cried Kitty, as she looked at 
 the bright streak, “it goes down and then up 
 again ; and I can see the beam slanting away from 
 the glass on each side, for all the world like a big 
 letter V! ” 
 
 “ Yes,” returned Humphry, “ you see the course 
 of the beam is stopped by the looking-glass, and 
 instead of going through it, the thread of light 
 that streams down from the hole in the shutter no 
 sooner falls on the mirror than it is driven up 
 from it, precisely in the same manner as if the 
 luminous particles were a series of hard balls pro- 
 jected against the glass, and so made to bound off 
 from its surface.” 
 
 The youth then called for his arc, and proceeded 
 to measure the angle at 
 which the light fell upon 
 the glass, and also the 
 angle at which it was 
 reflected from it, — thus: 
 “Do you see, Kitty,” 
 he cried, as the eager 
 girl stooped down beside her brother, “the ray 
 
THE WONDERS OF THE REFLEXION OF LIGHT. 379 
 
 that slants down from the shutter falls upon the 
 glass at an angle of 45°, and this is what is called 
 the angle of incidence ; while the ray which slants 
 upwards from it is reflected from the glass at 45° 
 also, and this is what is called the angle of re- 
 flexion : so that, you perceive, the one is exactly 
 equal to ihe other , and this constitutes what is 
 termed the law of reflexion . For, no matter what 
 the form of the mirror itself, or in what direction a 
 ray of light falls upon it, it is always reflected or 
 driven back from the surface at precisely the same 
 angle as it strikes upon it. As you say, the two 
 rays form a kind of letter V, and one prong 
 of the letter always slants just as much as the 
 other.” 
 
 “But suppose the surface of the glass, Hum- 
 phry, was to be hollowed out like a bowl, would it 
 do so then ? ” inquired the girl. 
 
 “ Certainly,” was the reply ; “ and if the rays 
 falling upon it then were parallel one to the other, 
 you would find, upon drawing the figure on paper, 
 that they would all meet together at one point in 
 front of the glass, which would, consequently, be 
 the focus, — the distance of such focus being equal 
 to half the radius , or semi-diameter , of the curva- 
 ture of the mirror itself Give me the compasses 
 and open the shutters, Kitty, and you shall soon 
 see what I mean.” 
 
380 
 
 THE WONDERS OF SCIENCE. 
 
 In a few minutes the following diagram was 
 described : — 
 
 Convex Mirror. 
 
 Concave Mirror. 
 
 “ There ! ” cried Humphry, as he put the last 
 touch to the drawing, “the two curved lines repre- 
 sent the surfaces of a convex and a concave mirror, 
 the curvatures of which form portions of a circle, 
 having its centre at the point where the unbroken 
 lines meet. Now, these unbroken lines, being 
 drawn in each case from the centre to the surface 
 of the mirror itself, are exactly perpendicular to 
 the points where the rays of light fall; and if you 
 measure with the arc the angle which the dotted 
 parallel lines form on one side of the unbroken 
 ones, you will find that they are, in every case, 
 here equal to that which the dotted slanting lines 
 form on the other side of the same perpendicular. 
 Consequently, you perceive that, by a concave 
 
THE WONDERS OF THE REFLEXION OF LIGHT. 381 
 
 mirror, the rays are made to converge to a focus in 
 front of the mirror itself ; whereas by a convex 
 mirror the rays are made to diverge , as if they 
 came from a focus behind the mirror itself. Now 
 this, you remember, is precisely the same as what 
 takes place with concave and convex lenses ; for a 
 concave lens has its focus in front of it, like a 
 concave mirror, but, owing to the rays passing 
 through the lens in the one case, and being driven 
 back from the mirror in the other, they are made 
 by the lens to diverge and by the mirror to con- 
 verge . So that, while the concave lens diminishes 
 the apparent size of objects, the concave mirror 
 magnifies them. The same thing holds good,” con- 
 tinued the boy, “ with a convex lens and a convex 
 mirror ; they both have their focus behind them, 
 but the rays, in passing through the lens, converge 
 to a point, whereas, being driven hack from the 
 mirror, they diverge ; and so, while the convex lens 
 magnifies , the mirror diminishes the apparent size 
 of objects.” 
 
 Next, Humphry directed his sister to place her- 
 self alongside the looking-glass over the mantel- 
 piece, while he did the same facing her, and in 
 such a manner that neither could see their own 
 figure reflected in the mirror. It would then be 
 found, he said, that they would each behold the 
 other, and at exactly the same distance behind the 
 glass as they were in front of it. In this manner : — 
 
382 
 
 THE WONDERS OF SCIENCE. 
 
 “ Now the reason why I see you,” said the lad, 
 “ and you see me in another place than we really oc- 
 cupy, is, because the rays reflected by the glass enter 
 our eyes in that direction ; and, as I told you before, 
 an object is always seen by us in the direction 
 which the ray has at the moment of reaching the 
 eye , without regard to what may have been its 
 course previously . Your image, of course, Kitty, 
 is on the surface of the glass itself, and not behind 
 it, as it appears to you to be ; and what, I dare say, 
 will sound stranger to you, is, that the image itself 
 upon the glass is exactly half the size that it seems 
 to be behind it: for since, when you look at your- 
 self in the glass, your image appears to be just as 
 far at the back as you are standing in front of the 
 
THE WONDERS OF THE REFLEXION OF LIGHT. 383 
 
 mirror, it is evident that the mirror itself must be 
 half-way between you and your apparent image; 
 so that it will cut in half the cone of rays which 
 enter your eye from the surface of the looking- 
 glass.” 
 
 “ There is a picture,” continued Humphry, as he 
 put the drawing before his sister, “ of a person 
 looking at himself in the glass; and you will see, 
 by the rays from his chin and forehead, which are 
 reflected in a point to the eye, that a vertical line 
 A ... B. at the surface of the glass, must be exactly 
 equal to half the length of the image, since the image 
 and the eye of the spectator are always at equal dis- 
 tances from the glass itself. But the image, which 
 appears to be behind the glass, is seen under the 
 same angle as the image, which is really on the 
 surface of it; and so, for the reasons I before gave 
 you, when speaking of the apparent size of objects 
 in general, the one behind the glass appearing to 
 be at twice the distance of the other, naturally 
 seems to be twice as large as the image on the 
 surface really is.” 
 
384 THE WONDERS OF SCIENCE. 
 
 “ I have already shown you, Kitty,” went on the 
 youth, after a pause, “ that if two persons stand in 
 front of a mirror, and each at opposite sides to it, 
 they will see one another, but not themselves; and 
 this constitutes the principle of what is termed the 
 c magician’s mirror.’ ” 
 
 “ Here is a plan,” said 
 Humphry, “ of the ordi- 
 nary arrangement. The 
 black lines we will suppose to represent the walls 
 of two adjoining apartments. At the end of each 
 of the rooms there is an aperture, made large enough 
 to place behind it a looking-glass that is capable of 
 reflecting the whole figure. In each of these aper- 
 tures there is inserted a sheet of plate-glass, which 
 is surrounded with a gilt frame, so as to have the 
 appearance of an ordinary mirror; and behind this 
 a real looking-glass is placed, slanting at an angle 
 of 45°, and so large, that a person looking into the 
 sheet of plate -glass cannot see the edges of the 
 slanting mirror behind it. With such an arrange- 
 ment, it is plain that a person looking into either 
 of the mirrors will not see himself, but any one 
 who may chance to be looking at the same time 
 into the mirror in the adjoining room. Conse- 
 quently, on looking into the mirror and believing 
 that he should see his own figure reflected in it 
 as in an ordinary looking-glass, his astonishment 
 will be great in beholding himself transformed into 
 
THE WONDERS OF THE REFLEXION OF LIGHT. 385 
 
 another person, or, indeed, into some living animal that 
 may be placed in front of the neighbouring glass.” 
 Kitty observed to her brother, that she remem- 
 bered having seen the same kind of an apparatus in 
 a booth in a fair ; and by it persons were said to 
 be shown their future lovers. 
 
 Humphry told her that it was by the same 
 means that people were made to see, apparently, 
 through paving-stones. 
 
 44 For if,” said the boy, 44 by the arrangement I 
 have explained to you, it is possible to see a figure 
 in another apartment — a brick wall intervening — 
 it is obvious that, by the same device, an object 
 placed on one side of a paving-stone could be 
 readily seen on the other.” 
 
 44 But the concave mirror,” continued Humphry, 
 44 is capable of producing far more wonderful effects, 
 for the image from this appears suspended in the 
 air; so that if the mirror and the object are hidden 
 from view, the effect is almost supernatural. This 
 illustration represents the arrangement usually em- 
 ployed in such cases, — 
 

 386 THE WONDERS OF SCIENCE. 
 
 “ Here you perceive, Kitty,” added the lad, “ the 
 two sides of a room, at the end of which there is a 
 square opening, with a picture-frame surrounding 
 it. Outside the room, in an adjoining apartment, 
 is placed a large concave mirror; and so arranged, 
 that when an object is set a little above the floor in 
 front of it, a distinct image of it may be formed in 
 the centre of the aperture at the end of the room, 
 where the spectators are assembled. Now, if the 
 opening be filled with smoke, that is made to rise 
 in clouds from a chafing-dish concealed outside, the 
 image of any object placed in the one focus of the 
 mirror in the adjoining apartment will appear in 
 the other focus at the centre of the frame, and seem 
 to be depicted on the clouds of smoke there as a 
 back-ground. It is a favourite experiment to place 
 a skull, strongly illuminated, in the outer apart- 
 ment, and to reflect an image of it amid the smoke, 
 so as to be visible to the spectators in the inner room. 
 The trick of the mysterious dagger, too, is very 
 popular. The ordinary way of performing this is 
 by placing a basket of fruit in the one focus of the 
 mirror, so that a distinct aerial image may be formed 
 of it in the frame. One of the spectators is then 
 desired to take some fruit from the basket; and as 
 he approaches for that purpose, a person, pro- 
 perly concealed, withdraws the real basket of fruit 
 with one hand, and with the other substitutes a 
 dagger, the image of which seems to strike at the 
 
THE WONDERS OF THE REFLEXION OF LIGHT. o87 
 
 body of the spectator, and the thrust of the bright 
 polished steel at his breast never fails to produce 
 a powerful impression. Now, it can scarcely be 
 doubted that a concave mirror was the principal 
 instrument by which the heathen gods were made 
 to appear in the ancient temples. Jamblichus 
 informs us, that the ancient magicians made the 
 gods visible to the people among clouds of incense. 
 And in the middle ages the Pontiff, Theodore San- 
 tabaren, who was celebrated for his power in work- 
 ing miracles, exhibited to the Emperor Basil of 
 Macedonia the image of his lost son, magnificently 
 dressed, and mounted on a superb charger. The 
 apparition of the youth seemed to rush towards his 
 father; and, throwing himself into his arms, va- 
 nished. This effect was doubtlessly produced by 
 reflecting the image of a picture of the emperor’s 
 son on horseback; and the picture being brought 
 nearer to the mirror, the image, of course, ap- 
 peared to advance until it reached the emperor’s 
 arms, where it naturally eluded his grasp. The 
 celebrated Benvenuto Cellini has left us an ac- 
 count of a more modern necromancy, in which he 
 himself took a part, in the middle of the sixteenth 
 century. 
 
 “ 6 It happens,’ says Cellini,” proceeded Humphry, 
 as he read the account to his sister, ‘ through a 
 variety of odd accidents, that I made acquaintance 
 
388 
 
 THE WONDERS OF SCIENCE. 
 
 with a Sicilian priest, who was a man of genius, 
 and well versed in the Latin and Greek authors. 
 Chancing one day to have some conversation with 
 him, when the subject turned upon the art of ne- 
 cromancy, I, who had a great desire to know some- 
 thing of the matter, told him that I had all my 
 life felt a curiosity to be acquainted with the mys- 
 teries of the art. The priest made answer, that the 
 man must be of a resolute and steady temper who 
 enters upon that study. I replied, that I had for- 
 titude and resolution enough, if I could but find an 
 opportunity. The priest subjoined, 6 If you think 
 you have the heart to venture, I will give you all the 
 satisfaction you can desire.’ Thus we agreed to enter 
 upon a plan of necromancy. The priest, one even- 
 ing, prepared to satisfy me, and desired me to look 
 out for a companion or two. I invited one Vin- 
 cenzio Romoli, who was my intimate acquaintance ; 
 and he brought another with him. We repaired to 
 the Colisseum ; and the priest, according to the 
 custom of necromancers, began to draw circles upon 
 the ground, with the most impressive ceremonies 
 imaginable. He likewise brought hither assafoetida, 
 several precious perfumes and fire, with some com- 
 positions also, which diffused noisome vapours. 
 As soon as he was in readiness, he made an open- 
 ing to the circle ; and having taken us by the hand, 
 ordered the other necromancer, his partner, to throw 
 
THE WONDERS OF THE REFLEXION OF LIGHT. 389 
 
 the perfumes into the fire at a proper time, entrust- 
 ing the care of the fire and the perfumes to the 
 rest; and thus he began his incantations. This 
 ceremony lasted above an hour and a half, when 
 there appeared several legions of devils, insomuch 
 that the amphitheatre was quite filled with them.’ 
 Cellini afterwards tells us, 6 that the necromancer 
 called by their names a multitude of demons, who 
 were the leaders of the several legions, and ques- 
 tioned them by the power of the eternal, uncreated 
 God, who lives for ever, in the Hebrew language, 
 and likewise in Latin and Greek, and then the amphi- 
 theatre was almost in an instant filled with demons, 
 more numerous than at the former conjuration. 
 The necromancer requested me to stand resolutely 
 by him, because the legions were now above a 
 thousand more in number than he had designed, 
 and, besides, these were the most dangerous. The 
 boy who had accompanied us was in a terrible 
 fright, saying that there were in that place a million 
 of fierce men, who threatened to destroy us; and 
 that, moreover, four armed giants of enormous 
 stature were endeavouring to break into our circle. 
 Yincenzio Romoli quivered like an aspen leaf. 
 Though I was as much terrified as any, I did my 
 utmost to conceal the terror I felt ; so that I greatly 
 contributed to inspire the rest with resolution. 
 But the truth is, I inwardly gave myself over as a 
 
390 
 
 THE WONDERS OF SCIENCE. 
 
 dead man. The boy placed his head between his 
 knees, and said, ‘ In this posture will I die, for we 
 shall all surely perish/ In this condition, con- 
 cludes Benvenuto, we stayed till the bell rang for 
 morning prayers/ ” 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 391 
 
 CHAPTER XVII. 
 
 THE WONDERS OF COLOUR AND PHOTOGRAPHY. 
 
 The young philosopher had now completed his in- 
 vestigations concerning the refraction and reflexion 
 of light. He had ascertained, — 
 
 1. That all substances in nature are divisible 
 into two classes, viz. luminous and non-luminous 
 bodies. 
 
 2. That luminous bodies send off rays of light 
 from them in all directions , and that such rays 
 proceed in straight lines while traversing the same 
 medium. 
 
 3. That non-luminous bodies are transparent , 
 or opaque ; that is to say, they either allow the 
 rays of light emitted by luminous bodies to pass 
 through them, or else they arrest their progress; 
 sometimes, in the latter case, driving them off from 
 their surfaces, and sometimes absorbing them. 
 
 4. That when a ray of light falls obliquely on a 
 transparent body it is, on entering it, refracted or 
 
392 
 
 THE WONDERS OF SCIENCE. 
 
 bent, in a greater or less degree, out of its previous 
 straight course. 
 
 5. That when a ray of light is driven off or re- 
 flected from opaque (or even transparent) bodies, 
 the angle of reflexion is invariably equal to the 
 angle at which the ray falls upon their surfaces. 
 
 As yet, however, Humphry had dealt only with 
 white or ordinary uncoloured light, and he was 
 now about to study the phenomena of colour itself 
 — to investigate the laws which regulate the pro- 
 duction of the varied tints on the earth, and to 
 ascertain, if possible, the means by which the soil 
 is painted with a thousand hues, and how the 
 colourless sunbeam becomes broken up into count- 
 less dyes as it falls upon the flowers and the rocks, 
 and is driven back by them to the eye, arrayed in 
 all the charm of variegated lustre. 
 
 “ How comes it,” said Humphry to himself, as 
 he thought over the subject, “ that the earth by 
 night is black and sombre, as if a pall were spread 
 over the dead globe — that the trees have then a 
 dim, spectral look — that the sky is dusky as a 
 canopy of smoke, and that the buildings seem like 
 masses of dense shadow darkening the air, so that 
 the world about us is as colourless as a cavern, and 
 the beauty of surrounding nature blotted out with 
 the universal gloom ? And how is it, too,” mused 
 the poetic boy, “ that the beams of the returning 
 sun have power to dye the fields and sky with the 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 393 
 
 richest hues — to crimson the clouds with the glow- 
 ing tints of dawn, and to revive, as it were, in an 
 instant, the infinite colours of the flowers, so that 
 the ground grows suddenly iridescent with their 
 various dyes ? How comes it, again, that at the 
 tropics, where the sun steeps the earth in a flood 
 of light, the plumage of the birds and the blossoms 
 of the plants are unrivalled for the gorgeousness of 
 their colours ; and that as we proceed thence to 
 colder climates we find a regularly declining chro- 
 matic scale, the tints becoming less and less vivid 
 till we reach the Poles, where Nature is arrayed in 
 one unvarying robe of white ? ” 
 
 Rut Humphry was too anxious to experiment 
 to continue dreaming over the matter, and, accord- 
 ingly, he got his sister to darken the room once 
 more, and then attaching a prism in front of the 
 hole in the shutter, he proceeded to throw the 
 spectrum on the wall in the manner before de- 
 scribed. 
 
 Kitty was as delighted as the boy with the 
 beauty of the image, nor could she help wondering 
 how it happened that a simple stick of white glass 
 could resolve the sunbeam into such exquisite 
 tints. 
 
 Humphry told her that the image she saw on 
 the wall was merely an oblong picture of the sun 
 itself, the orb being drawn out to that figure by 
 the refraction of the glass. The vividness of the 
 
894 
 
 THE WONDERS OF SCIENCE. 
 
 colours depends upon the smallness of the aperture 
 through which the light is admitted, and the dis- 
 tance of the screen upon which the spectrum is 
 made to fall; so that if the hole in the shutter were 
 smaller, and. the wall farther off, the spectrum 
 would be much brighter. The colours, he added, 
 came from the decomposition of the sunbeam into 
 its elementary tints. 
 
 “ You, doubtless, Kitty, think the light of the 
 sun to be simple and uncompounded, and little 
 dream that every ray of white light which meets 
 your eye is made up of seven other beams, and 
 each coloured with some one of the tints you see in 
 the spectrum here ; and it is solely because the 
 sunbeam is a compound rather than a simple thing, 
 and that each of the seven rays of which it is com- 
 posed have different properties and refrangibilities, 
 that this glass prism has the power of separating 
 them one from the other, and so of resolving the 
 compound beam into its seven elementary rays. 
 Look here,” he continued ; “ were it not for this 
 prism the beam which comes through the hole in 
 the shutter would proceed in its previous course, 
 and strike upon the floor ; but by means of this 
 instrument it is refracted , or bent out of its path, 
 and as the coloured beams of which it is composed 
 are, as I said, all differently refrangible, the red 
 ray here, being the least refrangible of all, is the 
 least bent out of its course, and so made to appear 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 395 
 
 at the bottom of the spectrum ; whereas the violet 
 ray, which is the most refrangible, undergoes the 
 most deviation, and thus is found at the upper part 
 of the coloured image.” 
 
 Kitty acknowledged that it was beyond her 
 power to comprehend how a beam of white light, 
 which appeared to her to be devoid of all colour 
 whatever, could be really composed of every kind 
 of colour. “ How was it possible,” she said, “ for 
 violet, and blue, and green, and yellow, and red, 
 when mixed together, to form white ? ” 
 
 Humphry smiled at his sister’s incredulity, and 
 said he would show her that it was quite possible 
 to put the parts of the sunbeam together again, — 
 for by the same means as he had decomposed the 
 white beam into its seven coloured rays, so would 
 he compound those seven coloured rays again into 
 one colourless beam.” 
 
 The girl was all eagerness to see the composite 
 nature of light thus practically demonstrated, and 
 in obedience to her brother’s instructions she pro- 
 ceeded to place a sheet of white pasteboard against 
 the wall, so that the spectrum might fall upon it, 
 and then to bring it gradually nearer the prism. 
 
 As Kitty did this, she noticed that the spectrum 
 grew smaller and dimmer ; but though the colours 
 began to mix and encroach upon one another as 
 she advanced towards the prism, she found that, 
 even when the pasteboard screen was brought close 
 
396 
 
 THE WONDERS OF SCIENCE. 
 
 to the face of the glass she could still recognise the 
 separation of the light into its elementary coloured 
 beams. 
 
 This done, Humphry proceeded to annex to the 
 prism already employed another, which was exactly 
 similar in all respects — being made of the like kind 
 of glass, and having a like refracting angle — to the 
 previous one. The second prism, however, was 
 placed in the opposite direction to the first, so that 
 while the base of the one was uppermost, that of 
 the other was underneath — as here shown : — 
 
 The reason of this arrangement was, as Hum- 
 phry explained, that the second prism might ex- 
 actly undo what the first had previously done, so 
 that the rays being now refracted by the one in an 
 opposite direction to the other, they would be all 
 brought together again, and made to strike upon 
 the same spot as they would have fallen upon had 
 no such instruments been interposed. 
 
 The apparatus being fixed, the ray from the hole 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 397 
 
 in the window-shutter no sooner passed through 
 the two prisms than the coloured spectrum which 
 the beam had been previously resolved into 
 vanished from the wall, and a round white spot 
 of light appeared upon the floor. 
 
 Kitty was so wonder-stricken at what she saw, 
 that she looked at Humphry with the same fixed 
 stare as a child gazes at some parlour magician. 
 
 “ You see, then, sister,” said the lad, “ that 
 seven coloured rays may be compounded again into 
 one white one, even as one white beam can be de- 
 compounded into seven coloured ones. So that, 
 incredulous as it may seem to you, it is impossible 
 to avoid the conclusion that white light is a com- 
 posite thing, and made up of a number of other 
 kinds of light that are widely different from it. 
 But,” continued Humphry, “ there is another and 
 simpler means of proving this point to you.” 
 
 For this purpose the girl had to procure from 
 the colour-shop seven different colours in powder, 
 each of the same tint as one of the rays in the 
 spectrum. These were afterwards mixed in the 
 same proportion as the rays themselves bore to one 
 another, and, to Kitty’s astonishment, the result 
 was a kind of greyish white , produced by the 
 mingling of the whole ; and Humphry told her 
 that, were it possible to obtain colours of precisely 
 the same tint as those in the spectrum, a perfect 
 white would be the consequence. 
 
>98 
 
 THE WONDERS OF SCIENCE. 
 
 “ Again,” the youth continued, “ if we take a 
 circle, and paint round it the several prismatic 
 tints in the same proportion as they exist in the 
 spectrum itself, and cause these to revolve so 
 rapidly that the eye is unable to see any one of 
 them , but rather perceives the whole at once, the 
 paper will no longer appear coloured like the rain- 
 bow to us, but seem really white as it flashes past 
 the eye.” 
 
 It was necessary, however, before doing this, to 
 measure the several lengths of the coloured spaces 
 in the spectrum itself, when it was found that the 
 various prismatic tints were in the proportions 
 hereunder given : — 
 
 Proportionate Width of the 
 Bands of Colours. 
 
 Violet 80 
 
 Indigo 48 
 
 Blue 60 
 
 Green 60 
 
 Yellow 40 
 Orange 27 
 
 Red 45 
 
 360 
 
 The next step was to colour a circular piece of 
 paper, as nearly as possible in the same manner as 
 the spectrum, and this was done after the following 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 899 
 
 fashion — where it will be seen that the outer coloured 
 circle is nothing more than the prismatic spectrum 
 bent round till its two ends meet at the point be- 
 tween the violet and red — the entire circle itself 
 being supposed to be divided ; "to 360 parts. 
 
 The circular spectrum, when finished, was placed 
 upon a humming-top, and the top being made to 
 spin as rapidly as possible, the prismatic disc, as 
 it whirled past the eye, appeared to be absolutely 
 colourless ; for each tint as it revolved left its im- 
 pression upon the retina but for an instant, and this 
 being immediately afterwards covered by the tint 
 which was next to it, the result naturally was, that 
 the whole of the seven colours fell upon precisely 
 the same part of the retina itself, and so produced 
 a composite impression — the seven coloured rays 
 being peroeived all at once, rather than one after 
 
400 
 
 THE WONDERS OF SCIENCE. 
 
 another. Hence the circle seemed to be devoid 
 of any one of the colours painted upon it, and to 
 partake of that white tint which naturally results 
 from the blending of the whole. 
 
 Humphry himself was almost as delighted as his 
 sister with the result of his experiments. It was 
 demonstrable that the light of the sun which fills the 
 air by day, and seems absolutely colourless to us, is 
 not of that simple homogeneous nature which we 
 are naturally led to believe, but really made up of 
 seven coloured rays, which the eye itself is unable 
 to separate, and from which proceed all the several 
 hues with which the earth is painted, for the 
 composite white beam falling upon the different 
 objects around is broken up by them into its ele- 
 mentary tints, and some one of these reflected by 
 them to us, so that the object itself naturally appears 
 of the same colour as the beam it sends to the eye. 
 
 Humphry had now to investigate the several pro- 
 perties of the spectrum itself. 
 
 It will be remembered that he before found the 
 point of greatest heat to exist at the very extremity 
 of the red ray, and he now ascertained by means 
 of a photometer (or an instrument for measuring the 
 relative intensity of different lights) that the point of 
 greatest light existed at the boundary of the orange 
 and the yellow rays. Consequently, as the red (or 
 calorific) rays were less refrangible than the yellow 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 401 
 
 (or luminous) rays, there was but one conclusion to 
 come to, — light was itself more refrangible than 
 heat; that is to say, the light in passing through 
 the prism, and being there separated from the heat 
 with which it was previously associated, was bent 
 farther out of its course than the heat was, so that 
 the two principles were differently acted upon by 
 the glass, and consequently possess different powers 
 and susceptibilities. 
 
 “ But if,” said Humphry, “ the red rays are the 
 calorific ones, and the yellow rays the luminous 
 ones, what peculiar properties belong to the rays at 
 the upper end of the spectrum, where the sunbeam 
 is bent the farthest of all out of its previous course ? 
 What special power appertains to the violet and blue 
 portion of the coloured image ? ” 
 
 The youth knew, from the books he had studied 
 upon the subject, that these constituted the che- 
 mical beams — that is to say, the violet extremity 
 of the spectrum had been found to possess the power 
 of separating silver from some of its compounds, and 
 Humphry was now anxious to observe the effect 
 for himself. 
 
 Having brushed a paper over with a solution of 
 nitrate of silver (lunar caustic), he placed a strip 
 of it a little way beyond the violet extremity of the 
 spectrum ; another strip he deposited in the violet 
 ray itself ; a third was left in the blue ray ; while 
 in each of the other coloured portions a piece of the 
 
 D D 
 
402 
 
 THE WONDERS OF SCIENCE. 
 
 same paper was exposed, and the light admitted to 
 them all at the same time. 
 
 It was then found that the nitrate of silver 
 darkened the most rapidly at that part of the spec- 
 trum a little beyond the violet extremity — that the 
 chemical effect was the greatest after this in the 
 violent ray itself. Next, the blue ray possessed a 
 greater decomposing power than the green ; whilst 
 in the yellow and red rays no such power was per- 
 ceptible, for the solution of silver remained un- 
 darkened there. 
 
 “ So, then,” cried Humphry, “ the wonderful 
 sunbeams that stream every day upon the earth 
 contain not only all the colours of the rainbow, but 
 three distinct, subtle principles, locked up in them 
 — heat, light, and chemical influence ; each of 
 these being differently refrangible and existing in 
 a ray of a different colour ; the heat inhering in 
 the red or lower portion of the spectrum, and the 
 chemical power in the violet or opposite extremity, 
 whilst the light occupies, as it were, a middle place, 
 residing principally in the yellow portion. 
 
 Humphry then delighted his sister by preparing 
 different chemical solutions, to be acted upon by the 
 violet rays of the sun. 
 
 First, he made some chloride of silver (by steep- 
 ing a paper in salt and water), and then brushing 
 it over with a solution of lunar caustic . This he 
 found to darken even more rapidly than the nitrate 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 403 
 
 of silver itself, and he then set to work to ascertain 
 the cause. 
 
 Now chloride of silver he knew to consist of 
 chlorine (a green coloured gas) and silver, and 
 he was anxious to see whether light would act 
 upon chlorine more powerfully than it did upon 
 nitric acid, as Mr. Wedgwood had told him. 
 
 Accordingly he filled ajar with equal portions of 
 hydrogen and chlorine gases, and submitted this to 
 the action of the sun’s rays, when, to the astonish- 
 ment of himself and terror of Kitty, the jar was no 
 sooner placed in the sunshine than the two gases 
 detonated with the noise of the report of a pistol, 
 and the jar itself was almost shivered to pieces in 
 the explosion. 
 
 Delighted with the result, and anxious to re- 
 peat the experiment in a less dangerous form, 
 he filled a tube, about half an inch in diameter 
 and twelve inches long, with the same gases, and 
 while the end of the tube was inserted in a vessel 
 of water, the upper part of it was shaded with an 
 opaque cover, so that by removing this for an 
 instant he could allow the gases within the tube 
 to be acted upon by the light for as short a time 
 as he pleased. 
 
 In this manner the ingenious youth found, that 
 the moment the opaque cover was removed and the 
 tube exposed, even to the diffused light of day, a 
 cloudiness appeared within it, owing to the in- 
 
404 
 
 THE WONDERS OF SCIENCE. 
 
 stantaneous, though silent, combination of the two 
 gases, while the water rose more or less rapidly 
 within it according to the intensity of the light. 
 The effect even of a passing cloud was thus dis- 
 tinctly seen to retard the rapidity of the combina- 
 tion, while, when exposed to the full solar light, 
 the union of the two was so instantaneous that the 
 gases suddenly disappeared from the tube, and 
 the water rushed violently up into it to fill the 
 vacuum. 
 
 Next Humphry found that the two gases, when 
 exposed to the sun’s rays in a tube of violet-coloured 
 glass, combine rapidly, but, strange to say, without 
 explosion ; whereas when they are submitted to 
 the action of sun-light in a tube of red glass, the 
 gases scarcely act upon one another. It was, 
 moreover, ascertained, that when standing in a 
 perfectly dark place, the two gases do not enter 
 into combination in any length of time. 
 
 The lad could now understand why the chloride 
 of silver darkened so rapidly in the sun’s rays. 
 The chlorine with which the metal was combined 
 was attacked by the moisture in the atmosphere, 
 and as this moisture consisted of oxygen and hy- 
 drogen in the form of water, the hydrogen of it 
 was made by the chemical influence of the sunbeam 
 to enter into rapid combination with the chlorine, 
 and thus the silver was left behind, but in such 
 minute particles that the metal, instead of appearing 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 405 
 
 white as it usually does, assumed the form of a 
 black powder, which, being fixed in the paper, 
 naturally caused it to darken in those parts where 
 the light had fallen upon it. 
 
 Filled with the knowledge he had thus obtained, 
 Humphry set to work to produce some sun-pictures 
 for his sister. Patterns of pieces of lace were thus 
 made to impress their forms in a few seconds upon 
 paper that had been prepared over-night with a 
 coating of chloride of silver. Where the light fell, 
 the silver was separated from the chlorine, and 
 precipitated in minute black particles, so that the 
 paper was darkened in those parts ; while in the 
 places where the threads of the lace prevented the 
 rays from reaching the paper, the solution was un- 
 decomposed, so that a white line exactly corre- 
 sponding to the pattern of the lace itself became 
 impressed upon the black ground. 
 
 Kitty was overjoyed at the first picture she 
 beheld her brother produce by the light, and 
 Humphry smiled as he saw her take it to the 
 window to examine it more minutely, for he knew 
 that as she looked at it the light would begin to 
 act upon the parts that had been previously screened 
 by the lace itself, and where the solution still re- 
 mained undecomposed in the paper ; and sure 
 enough, in a few minutes, she gradually saw the 
 pattern vanish, and the whole ultimately become of 
 one uniform dark-brown tint. 
 
406 
 
 THE WONDERS OF SCIENCE. 
 
 “ What a pity,” cried the girl, “ that so beautiful 
 a thing should be so perishable ! If you could only 
 find out, Humphry, how to fix the pictures, what a 
 great thing it would be for you to do ! ” 
 
 The brother told her, that in order to accomplish 
 this it was necessary to discover some substance that 
 would remove the undecomposed chloride of silver, 
 forming the white parts of the picture, and which 
 would not attack the decomposed silver itself, 
 forming the dark parts of it. 
 
 To attain this end, the young chemist made 
 an infinity of experiments, but without avail ; 
 for though he tried a number of acids and alkaline 
 solutions, he could find no liquid that would remove 
 the undecomposed chloride from the paper, and after 
 weeks of toil and disappointment he was obliged 
 to confess, unwillingly, that the difficulty was one 
 he lacked the power to master. 
 
 Many years after Davy’s time, however, it was 
 discovered that the chemical substance termed hypo- 
 sulphite of soda readily dissolves chloride of silver, 
 and has little or no action upon the precipitated 
 silver itself ; and from this period may be dated the 
 perfection of the wonderful art of photography (or 
 sun-painting) that Thomas Wedgwood was the first 
 to attempt, and at which Davy himself was one of 
 the early but unsuccessful experimenters. 
 
 Of this art there are now two distinct branches, 
 viz. one in which the pictures are produced upon 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 407 
 
 metal, the other upon paper or glass. In the me- 
 tallic process, iodide of silver * is the chemical agent 
 rather than the chloride ; this is formed by sub- 
 mitting a perfectly clean plate of polished silver to 
 the action of the vapour of iodine, and sometimes 
 to bromine afterwards, in order to quicken the 
 action. The plate thus prepared is placed in the 
 camera, so that an image of the object to be copied 
 may fall upon it ; the consequence is, that in the 
 “ lights ” of the picture the iodide of silver becomes 
 decomposed, the iodine itself going off in the form of 
 hydriodic acid gas, by combining with hydrogen in 
 the moisture of the air, and the pure silver being 
 left behind ; whereas in the shades of the picture 
 where no light reaches, the iodide of silver remains 
 undecomposed. The action usually takes place in 
 some few seconds, according to the intensity of 
 the light and the nature of the “ quick” used. 
 When the plate is removed from the camera no 
 picture is visible upon its surface, so that the deve- 
 loping part of the process has then to be performed. 
 This consists in submitting the plate to the fumes 
 of mercury, which attach themselves to the parts 
 where the pure silver has been separated from the 
 iodine with which it was combined. These parts 
 constitute, as we said before, the “ lights ” of the 
 picture, and there the mercurial vapour is con- 
 densed, and clings in the form of minute globules ; 
 whilst to the parts which have been undecomposed 
 
408 
 
 THE WONDERS OF SCIENCE. 
 
 the mercury does not attach itself, having no affinity 
 whatever with the iodide of silver that remains there* 
 The consequence is, the globules of mercury which 
 cling to the portions where the rays have fallen, 
 reflect so much light to the eye that they form the 
 “ whites” of the picture; whereas the undecom- 
 posed iodide of silver, sending no light to the re- 
 tina, constitutes the “ blacks :” and thus the image, 
 which was latent on the plate, is developed, or 
 brought out, with such marvellous fidelity, that 
 when examined with a microscope, characters that 
 were several miles distant in the original may be 
 clearly read in the minute sun-copy. 
 
 After this comes the fixing process, and that con- 
 sists merely in submitting the plate to the action of 
 hyposulphite of soda , which dissolves, and so re- 
 moves all the undecomposed iodide of silver from 
 it, and thus renders it incapable of being further 
 acted upon by the light. 
 
 The above constitutes what is now usually known 
 as the “ Daguerreotype process.” 
 
 The production of photographic pictures upon 
 paper, on the other hand, forms what is termed the 
 “Talbotype process” — the names of the two types 
 being derived from those of their inventors. In 
 the latter method of producing sun-pictures there 
 are almost the same different stages to be gone 
 through. The paper itself has first to be iodised, 
 or rendered sensitive to the action of light, by 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY, 409 
 
 means of coating it with a surface of iodide of 
 silver. This is done by washing it over first with 
 a solution of nitrate of silver, and when this is 
 dry, with a solution of iodide of 'potassium ; the 
 consequence is, the one solution decomposes the 
 other, so that nitrate of potash and iodide of silver 
 are formed. The nitrate of potash, being soluble, 
 is then washed out of the paper, while the in- 
 soluble iodide of silver remains fixed in it. Then 
 follows the “ quickening ” part of the process. 
 This consists in washing the sheet of iodised paper 
 over with a solution of what is termed gallo-nitrate 
 of silver, which consists of a small proportion of 
 gallic acid (the acid from gall-nuts) dissolved in 
 water, and added to a solution of lunar caustic, 
 having a little acetic acid, or pure vinegar, in it. 
 The gallic and acetic acids are used because it is 
 found that the presence of any vegetable or organic 
 matter hastens the decomposition of nitrate of 
 silver when exposed to light. The paper is now 
 ready for the camera, and is so sensitive to the 
 action of light that it is said to transcend the 
 ordinary iodised paper in this respect more than 
 a hundredfold, so that even a second or two of time 
 is sufficient to impress a latent image upon it. 
 
 Then, as in the daguerreotype method, the de- 
 veloping process has to be resorted to in order to 
 bring out the picture, which is imperceptible on re- 
 moving the paper from the camera, and the exist- 
 
410 
 
 THE WONDERS OF SCIENCE. 
 
 ence of which would not be suspected by any one who 
 had not been forewarned of it by previous experi- 
 ments. To render the picture visible, the paper 
 is washed over once more with the gallo-nitrate of 
 silver before described, and then warmed gently 
 before the fire ; whereupon that part of the paper 
 upon which the light has acted begins to darken, 
 while the other part of the paper retains its white- 
 ness. After this, as in the “Daguerreotype” 
 method, the fixing process has to be resorted to. 
 This, for “ Talbotypes,” consists in washing the 
 paper in bromide of potassium, which dissolves out 
 all the undecomposed chemicals, and so leaves an 
 indelible impression behind. 
 
 The picture thus produced, however, is what is 
 termed a “negative” one, — that is to say, the 
 lights in the original are represented by shades in 
 the photographic copy, and vice versa , the shades 
 in nature are rendered as lights in the picture. 
 The Talbotype, therefore, has to be again copied, 
 in order that the lights and shades may be accu- 
 rately represented. For this purpose, however, 
 the paper need not be so highly sensitive ; so that 
 the ordinary quickening part of the process by 
 means of the gallo-nitrate may be dispensed with, 
 or the paper may be coated with chloride of silver 
 instead of the iodide before described. Again, the 
 developing process is no longer necessary, the pic- 
 ture being produced directly by the action of light, 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 411 
 
 rather than indirectly by means of some developing 
 agent. The fixing process in this stage is usually 
 performed by means of hyposulphite of soda, and 
 by these means the negative picture before pro- 
 duced is rendered positive, and the lights and 
 shades thus made an accurate representation of 
 those in nature. 
 
 It will now be seen that the art of producing 
 sun-pictures, whether by the Daguerreotype or the 
 Talbotype, comprises usually four distinct pro- 
 cesses, viz.: — 
 
 1. The preparatory process, which consists in 
 preparing the plate or paper, — that is to say, in 
 coating it with some solution of silver that is 
 capable of being decomposed by the action of 
 light. 
 
 2. The quickening process, which consists, again, 
 in rendering the plate or paper more highly sensi- 
 tive to light by the addition of some other chemical, 
 which facilitates the decomposition of the com- 
 pound of silver, with which the surface has been 
 previously coated. 
 
 3. The developing process, which consists in 
 rendering visible the latent picture which has been 
 impressed upon the plate or paper while exposed 
 to the action of the light in the camera. 
 
 4. The fixing process, or the dissolving out of 
 all the undecomposed silver compound, and so pre- 
 
412 
 
 THE WONDERS OF SCIENCE. 
 
 venting tlie light from having any further action 
 upon it. 
 
 Now it must not be supposed that the com- 
 pounds of silver are those only which are capable 
 of being decomposed by the sun’s rays, for photo- 
 graphic pictures have been produced by compounds 
 of all the precious metals — such as gold, platinum, 
 mercury, & c., these substances having but slight 
 affinities, and so being easily separable from the 
 elements with which they are united. Again, iron 
 has been used successfully for the same purpose, — 
 for this body, also, is readily decomposed when 
 combined with certain substances. Further, the 
 gum -resins and bitumens admit of being em- 
 ployed in the same manner, and many vegetable 
 juices have been used by Sir John Herschel for 
 a like purpose. Indeed it has been truly said, 
 that almost every substance in nature is affected, 
 in some way or other, by the solar rays, for we 
 now know that no substance can be exposed to the 
 sun’s rays without undergoing chemical action. 
 
 The changes, therefore, that are continually oc- 
 curring in the external world are quickened by the 
 rays, which at one time, it was believed, gave only 
 light and heat to the globe that we inhabit ; and 
 even the very changes of the seasons, the growth 
 of vegetation, the blossoming of the flowers, and 
 the ripening of the fruits, are all due in a measure, 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 413 
 
 to the chemical influence of those elementary rays 
 which lie concealed in the compound sunbeam : 
 for it has been proved that the sunshine itself is 
 necessary, even to the breathing of plants through 
 their leaves, and that in the shade they cease ab- 
 sorbing the carbon from the atmosphere which is 
 ultimately destined to form part of their woody 
 structure. Thus light becomes not only the source 
 of beauty to the world, and the agent upon which 
 one of our most wondrous senses depends, namely, 
 that by which we are enabled to recognise the 
 form and nature of objects at a distance from us, 
 but it is also the source of health and vigour to 
 our frames, by maturing the products of the earth 
 upon which we live, as well as by promoting in 
 our own frames those subtle, chemical changes, by 
 which our bodies are nourished and our faculties 
 developed, since in darkness men can no more 
 thrive than plants. 
 
 Had Davy lived to see the development of the 
 chemical influence of light that has been opened up 
 to us since his time, he would have been the loudest 
 in his praises of the marvels wrought by it, and, 
 doubtless, among the foremost to have extended 
 our knowledge of its action. But these are dis- 
 coveries made since his time, and discoveries which 
 he, with his deep insight into Nature, was unable 
 to foresee, or even to assist. To such perfection, 
 however, has the photographic art been carried 
 
414 
 
 THE WONDERS OF SCIENCE. 
 
 since the days when Davy vainly essayed to fix the 
 images which took him some quarter of an hour to 
 produce, that not only can stationary objects have 
 their forms indelibly impressed upon paper by the 
 very light itself which renders those forms visible to 
 us, but the passing shadows that give beauty to the 
 landscape can be made permanent, the very undu- 
 lation of the corn can be seized, the rustling of the 
 leaves detained, and even the rippling of the waters, 
 the playing of the fountains, and the curling of the 
 smoke, whose particles never for two moments to- 
 gether remain in the same place, can be arrested, and 
 their evanescent forms painted by themselves, as it 
 were, upon the tablets ; so that the effect of a mere 
 instant can, by its marvellous agency, be prolonged 
 for years. Thus time, which is known to us only 
 by the changes which are continually occurring with- 
 out and within us, has all the fixity of space ; and 
 those historical events which our forefathers were 
 unable to convey to us, from the want of some such 
 art, can now be handed down, rendered with all the 
 truth of light itself, so that future generations 
 gazing at them may behold the same scenes that 
 were impressed at the back of our eyes years 
 before. Indeed, the photographic art itself is but 
 the process of individual and transient vision made 
 universal and permanent ; for the eye itself is but 
 the camera through which we gaze at the world 
 without, and the retina at the back of the organ of 
 
THE WONDERS OF COLOUR AND PHOTOGRAPHY. 415 
 
 sight no more than a photographic plate, as it were, 
 impressing the images that flit before our vision 
 more or less permanently upon our memories. 
 
 As an instance, however, of the perfection, we 
 repeat, to which this process of fixing the most 
 transient images has been carried, we need only 
 mention the experiment performed by Mr. Talbot, 
 in which a moving body, that was made to revolve 
 at an enormous speed, and that was illuminated but 
 for an instant by the electric spark, was photo- 
 graphed as a stationary object. 
 
 It is well known that a wheel revolving at a 
 rapid rate is barely visible to us, the spokes 
 passing with such velocity before the eye that we 
 are unable to distinguish one from the other, so 
 that the whole appears to us almost as one entire 
 disc ; such a wheel, however, if made to rotate 
 in the dark, and then suddenly illuminated for that 
 inappreciable portion of time which the electric 
 spark — the miniature lightning of the laboratory — 
 endures, then appears to us as if absolutely standing 
 still ; for as we see it under such circumstances 
 only in that place which it occupies so long as 
 the light lasts, and this being but for the least 
 conceivable term of duration, it has no time — 
 however rapidly it may be turning on its axis — 
 to pass from one point of space to another, so that 
 it can but appear to us as if utterly stationary. 
 
 In the experiment we allude to, a wheel was 
 
416 
 
 THE WONDERS OF SCIENCE. 
 
 thus made to revolve so rapidly, that its revolu- 
 tions were counted by the musical note produced 
 by the vibrations of a spring, that moved back- 
 wards and forwards once at each turn. The revo- 
 lutions were performed in the dark ; and during 
 this the chamber and wheel were suddenly lighted 
 by one spark drawn from a powerful electric 
 machine. At this moment a photographic ap- 
 paratus was presented to the wheel itself, and on 
 developing the image thus produced upon the 
 paper which had been previously inserted in the 
 camera, it was found to be impressed with a per- 
 fect copy of the wheel itself, with all its spokes 
 distinctly visible, and precisely the same as if the 
 image had been taken from the wheel while in a 
 state of rest. It was the same stationary image, 
 too, as the spectators themselves had beheld during 
 the instantaneous illumination of the object ; and 
 thus, by the aid of the same fluid as the light- 
 ning itself, and with the assistance of music to 
 register the rate of revolution, that mysterious 
 principle of motion which has puzzled philosophers 
 since philosophy began, was made to appear like 
 rest, and even the sensibility of the eye itself 
 rivalled by photographic agency, so that the dead 
 paper was made to be impressed with the very 
 same figure as the living retina itself perceived. 
 
CONCLUSION. 
 
 417 
 
 CHAPTER XVIII. 
 
 CONCLUSION. 
 
 During the prosecution of his later experiments 
 Humphry had formed the acquaintance of Mr. 
 Davies Giddy, a gentleman of high scientific attain- 
 ments, better known under the name of Davies 
 Gilbert, and who was then resident at Tredrea, 
 near Penzance. 
 
 This gentleman, who ultimately became Pre- 
 sident of the Royal Society, proved of great ser- 
 vice to young Davy, for not only did he lend the 
 boy such apparatus as he required for the carrying 
 out of his experiments, but he delighted to con- 
 verse with Humphry ; and though he could not 
 help smiling occasionally at the strangeness of his 
 theories, he grew to have a lively sense of the 
 ardour of the youth’s imagination, and the ori- 
 ginality of his mind. 
 
 Now it so happened that Davies Giddy was 
 
 E E 
 
418 
 
 THE WONDERS OF SCIENCE. 
 
 acquainted with Dr. Beddoes, who had formerly 
 been one of the Oxford Professors, but who had 
 recently opened a Pneumatic Institution at Bristol 
 for the cure of diseases by the inhalation of gases ; 
 and it was during one of Dr. Beddoes’ visits to 
 Davies Giddy that Humphry made the acquaint- 
 ance of the Doctor, and so favourable an im- 
 pression did he make upon the gentleman, that 
 not long afterwards a letter was sent, offering 
 Humphry the post of Assistant to the Bristol 
 Institution. 
 
 The lad was delighted at the prospect of re- 
 moving from so remote a place as his native town, 
 and lost no time in talking the matter over with 
 his friends. Mr. Giddy told him of the Doctor’s 
 influence, and how his Institution was already the 
 resort of some of the most eminent persons in the 
 country, and warmly advised him to avail himself 
 of the offer. 
 
 Mr. Borlase, to whom Humphry repeated all that 
 Mr. Giddy had said, counselled the boy to take the 
 same step, and added, that he had been so pleased 
 with his conduct while under his roof that he 
 would in no way impede his advancement, but 
 would rather cancel his indentures, even though 
 he was just beginning to be of service to him. 
 
 Mrs. Davy, too, was anxious that her boy — 
 whom she felt more and more convinced was 
 destined to take a high rank in the world — should 
 
CONCLUSION. 
 
 419 
 
 be transferred to a wider sphere, where his abilities 
 would have greater chance of being called into play, 
 and she gladly accompanied Humphry to their old 
 friend, Mr. Tonkin, to break the matter to him, and 
 hear what he thought of the proposal. 
 
 The old gentleman, however, could not be made 
 to listen to the project, and did not hesitate to 
 denounce Humphry’s desire for worldly honour as 
 the “ wild-goose chase” which led many an am- 
 bitious simpleton astray, saying, that if the boy 
 would make up his mind to settle in his native 
 place, he might be assured of a comfortable inde- 
 pendence, for he would find but few able to com- 
 pete with him there. Nevertheless, in a large town 
 — however striking his talents might appear in a 
 small one — the circle of his competitors would be 
 so much increased, that he would sink into a mere 
 nobody, and end his days as one of the many fools 
 who had struggled after the world’s prizes, and 
 found, when too late, that there was no chance of 
 obtaining them. 
 
 Mrs. Davy, however, mother-like, felt satisfied 
 that Mr. Tonkin took an erroneous view of her 
 son’s powers, and she strove to assure her old 
 friend that he did not know what Humphry was 
 capable of doing so well as she did, and that if he 
 did, he would have as little fear as herself of his 
 failure. 
 
 Mr. Tonkin, however, was not to be argued out 
 
420 
 
 THE WONDERS OF SCIENCE. 
 
 of the notion he had taken up, and ultimately grew 
 so annoyed with what he fancied to be merely a 
 mother’s silly prejudice on Mrs. Davy’s part, that 
 he ended the interview by vowing that the boy 
 should never quit Penzance with his consent. 
 
 This, for a time, put a stop to the correspondence 
 on the subject. At length, however, Dr. Beddoes 
 became so urgent that Humphry should join him, 
 that, despite the objections of Mr. Tonkin, who 
 still would not listen to the plan, his friends ad- 
 vised him to accept the offer ; and it was accord- 
 ingly arranged that young Davy should leave Pen- 
 zance as soon as he conveniently could. 
 
 Accordingly, on the 2d of October, in the year 
 1798, Humphry, not then twenty years of age, 
 quitted his native town for the first time in his life, 
 and that to commence fighting his way in the world. 
 
 His mother parted from him as full of high hope 
 as the boy himself; and as the boy hugged the widow 
 to his heart alone in her chamber, before he left 
 her, he said, with the sobs in his throat, “ Mr. 
 Tonkin does not know me, mother, yet: but be 
 you of good cheer, I will live to be an honour and 
 a glory to you still ; and it shall be my proud lot to 
 say some day, that I was the means of raising you 
 and all that belong to me to a position of comfort 
 and eminence. Years ago now, mother, I told you 
 I would do it, and the resolve is still deep in my 
 heart.” 
 
CONCLUSION. 
 
 421 
 
 Mrs. Davy assured him she had every confidence 
 in his attaining the noble object he had in view, 
 and she parted from him, though with tears in 
 her eyes, with a smile of high hope upon her lip. 
 
 Mr. Tonkin, however, was resolute to the last, 
 and at his leave-taking denounced Humphry’s 
 plans as visionary schemes ; and when the boy had 
 left, and the old gentleman found his favourite 
 plan of settling Humphry in his native town as 
 a surgeon had been thwarted, he altered his will, 
 and revoked the legacy of the house that he had 
 previously bequeathed to his foster-son. 
 
 On young Humphry’s journey to Bath he met 
 his friend Mr. Davies Giddy at Oakhampton, and 
 while breakfasting there, the mail-coach from 
 London drew up at the door of the inn, covered 
 with laurels and ribbons, and bringing the first 
 news of Nelson’s victory of the Nile. 
 
 “ I have a greater fight than that to fight,” said 
 Humphry to himself ; “ and, please God, I will 
 gain the victory, too.” 
 
 It was Mrs. Davy’s happy lot to witness the 
 realisation of all the hopes she had formed of her 
 boy in his youth ; for, during her life, he rose to 
 be elected President of the Royal Society, and to 
 be created a Baronet, for the many additions he 
 had made to the stock of knowledge; to be re- 
 
422 
 
 THE WONDERS OF SCIENCE. 
 
 warded with the first prize instituted by the 
 Emperor Napoleon for the greatest scientific dis- 
 covery of the time ; and to be allowed a free passage 
 through France at a time when all other English- 
 men, no matter how high their rank or character, 
 were denied admission into that country. 
 
 THE END. 
 
INDEX, 
 
 Air, currents of, how caused, 166 
 Air-pump, experiments with, 216 
 Animal mechanism, wonders of, 70 
 Argand-burners, why superior in bril- 
 liancy, 278 
 
 Artificial light dependent on heat, 275 
 
 Bath wells, temperature of the, 107 
 Blow-pipe, cause of the increased 
 heat produced by the, 278 
 Brocken, spectre of the, in the Hartz 
 mountains, 352 ; philosophy of, 355 
 
 Camera, images produced in, 316; 
 why reversed, 344; how the lens 
 intensifies images in the, 349 ; cause 
 of variation in the size of objects 
 in, 350 ; pictures must be projected 
 on an opaque body, 352 
 Cellini, Benvenuto, and the necro- 
 mancer, 389 
 
 Chlorine, experiments with, 259 
 Coal, power concentrated in, 92 
 Coal-mine, destructive explosion in, 
 76 
 
 Colours, curious result from mixing 
 in certain proportions, 397 
 Combustion, laws of, 95; phenomena 
 of, 225 ; nature of, 239 ; experi- 
 ments in, 227 ; philosophy of, 264 
 
 , spontaneous, 242, 252 
 
 Corpse candles, philosophy of, 241 
 Creation, the wondrous story of, 98 
 
 Daguerreotype process of photo- 
 graphy, 408 
 
 Dew, deposition of, 126 ; less plentiful 
 in cloudy weather, 128 ; its laws, 
 129 
 
 Drummond light, the, 274 
 
 Earthquakes, 108 
 Electric light, 274 
 
 Ether, its powers of vaporization, 204 
 Explosive substances, 241, 244, 246 
 Eye, the, wonderful construction of, 
 69 
 
 Fire-damp not inflammable by red 
 heat, 253 ; rapidly explodes at white 
 heat, 254; explosible only when 
 mixed with atmospheric air, 281 
 Flame, subterranean, 107 
 
 , nature of, 265, 271 ; of a candle 
 
 hollow, 276 ; experiments with, 279 
 Fluids, expansive power of, 182 
 Fulminates of the precious metals, 
 247 ; gold, 248 ; mercury, 248 ; 
 silver, 249 ; platinum, 250 
 
 Gas, its first application to illumina- 
 tion, 91 
 
 Glass absorbs artificial, but transmits 
 solar heat, 139 
 
 Hastings, the French coast sometimes 
 visible from, by refraction, 332 
 Heat, natural sources of, 98 ; celestial, 
 100; subterraneous, 102-106; me- 
 chanical production of, 111 ; che- 
 mical, 112 ; combustion, 114 ; respi- 
 ration, 113 ; communication of, 116 ; 
 radiation, 119 ; reflexion, 130 ; dif- 
 ference between solar and terrestrial, 
 138 ; transmission of, 138 - 141 ; 
 absorption of, 143; degrees of, in 
 the spectrum, 142 ; relative absorb- 
 ing and radiating powers of sur- 
 faces, 145 ; radiation by different 
 colours, 146 ; solar more powerful 
 reflected than direct, 148; conduc- 
 tion, 149 ; wonderful effects of, 173; 
 expansive power of, 176; latent, 
 192 ; white, 224 ; artificial, curious 
 changes in its character at high 
 rates of temperature, 224 ; then 
 assumes all the properties of solar, 
 224 
 
 Hot-springs and wells, 107 
 Ignesfatui, how produced, 240 
 Jack-o'-lanterns, causes of, 240 
 Land’s End described, 25 
 
424 
 
 INDEX 
 
 Lens, magnifying power of the, how 
 determined, 363 
 
 Light, electric, 274 ; artificial, depend- 
 ent on heat, 275 ; rays of, travel in 
 straight lines, 318, 391 ; refraction 
 of, 324, 331 ; experiments, 325 ; rays 
 of, assume the colour of objects 
 from which they are reflected, 341 ; 
 reflexion of 379 ; compound nature 
 of a ray of, 894 ; composed of seven 
 colours, 395 
 
 Lightning, varieties of, 110 
 Liquids imperfect conductors of heat, 
 157; merely solids whose particles 
 are kept apart by heat, 192 
 Lucifer-matches,, why so readily in- 
 flammable, 252 
 
 Luminosity, temperature at which 
 bodies assume, 223 
 
 Magician’s mirror, the, explained, 384 
 Mail-coaches, the first, 91 
 Metals, their relative power of con- 
 ducting heat, 152 ; expansion and 
 contraction of, 177 ; practical appli- 
 cation of this power, 178 ; cooling 
 of, 219 
 
 Microscope, principle of the, 36-7-378 ; 
 
 the single, 369 ; the compound, 372 
 Mirage, an optical illusion caused by 
 refraction, 331 
 
 Mirrors, concave, experiments with, 
 130; wonders produced by, 385; 
 different effects produced by me- 
 tallic and glass, 136 
 Mont Blanc, ascent of, 92 ; ebullition 
 on summit of, 210 
 
 Objects, why they diminish in size in 
 proportion to distance, 358; mag- 
 nifying of, by lenses, 360 
 Oceanic currents, direction of the, 170 
 Oils, lamp, philosophy of the com- 
 bustion of, 255, 273 
 
 Palissy, Bernard, his discoveries in 
 pottery, 307 
 
 Pendulum, compensation, principle 
 o'f the, 180 
 
 Phlogiston, an imaginary principle, 
 225 
 
 Photography, .first experiments in, 
 309-405 ; practice of, 407 
 
 Prism, the spectrum produced by, 
 merely an oblong figure of the sun, 
 393 ; its colours the decomposition 
 of the sunbeam into its elementary 
 tints, 394 
 
 Pyramids of Egypt, size of the, 92 
 Pyrophorus, how produced, 241 
 
 Radiation, power of, in different sub- 
 stances, 124 
 
 Ramsgate, Dover Castle rendered 
 visible from, by refraction, 334 
 Refraction of light, curious property 
 of, 331 ; illusions caused by extra- 
 ordinary instances of, 332, 334 
 Respiration, philosophy of, 68 
 
 Safety-lamp, first glimmer of the, 75 ; 
 experiments with, 265 ; completion 
 of the first, 283 ; its perfected form, 
 289 ; value and importance of the 
 invention, 281 
 
 St. Michael’s Mount, Cornwall, 57 
 Science, true, its nature, 69 
 Scoresby’s, Captain, observation of a 
 distant ship by refraction, 339 / 
 
 Secretion, marvels of, 67 
 Spectrum, proportions of prismatic 
 tints in the, 398 ; circular, 399 
 Spontaneous combustion, 242-252 
 Steam, difference of heat in high and 
 low pressure, 158 
 Steam-boat, the first, 89 
 Sun-pictures, the earliest, 309 
 
 Talbot, Mr. Fox, his curious experi- 
 ment of photographing a rapidly 
 revolving -wheel, 415 
 Talbotype process of photography, 
 408 
 
 Telescope, principle of the, 365, 372 
 Temperature, rate of increase below 
 • the surface of the earth, 104 
 
 Vaporizable liquids readily explosible, 
 254 
 
 Vision, range of, 358 
 Volcanoes, 108 
 
 'Will-o’-the-wisp, philosophy of, 240 
 Wire-gauze, its power of resisting 
 flame, 288. 
 
 London : Printed by Thomas Harbild, Salisbury Square, Fleet Street. 
 

 
 
 
 
 
 
 
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