.ESSAYS , 
 
 BIOGRAPHICAL 
 
 AND 
 
 CHEMICAL 
 
 BY 
 
 SIR WILLIAM RAMSAY, K.C.B. 
 
 COMMANDEUR DE LA LEGION D'HONNEUR 
 
 COMMENDATORE DELLA CORONA D'lTALIA 
 
 FELLOW OF THE ROYAL SOCIETY, ETC. 
 
 NEW YORK 
 E. P. BUTTON ANB COMPANY 
 
 29 WEST 23RD STREET 
 1909 
 

 C -BAL 
 
PREFACE 
 
 THESE Essays on Chemical History and Biography, and on 
 chemical topics, have been delivered as lectures, or pub- 
 lished as magazine articles at various times in the course 
 of the last twenty-five years. A little alteration has been 
 necessary to avoid undue repetition, and in some cases 
 footnotes have been added, to correct statements which 
 have been rendered inaccurate by the progress of dis- 
 covery. 
 
 I have to thank the University of Glasgow for permis- 
 sion to reprint the oration on Black ; the editor of the 
 Youth's Companion for permission to reprint the sketch 
 of Lord Kelvin, ' What is an Element ? ' ' On the Periodic 
 Arrangement of the Elements,' 'Radium and its Pro- 
 ducts,' ' What is Electricity ? ' and ' How Discoveries are 
 Made ' : the editor of the Contempora/^y Review for 
 permission to reprint the article on * The Becquerel Rays ' : 
 and the Royal Society, which has kindly granted similar 
 permission to republish the life of M. Berthelot. 
 
 WILLIAM RAMSAY. 
 
 October 1908. 
 
 195100 
 
CONTENTS 
 I. HISTORICAL ESSAYS 
 
 PAGE 
 
 THE EARLY DAYS OF CHEMISTRY ... 1 
 THE GREAT LONDON CHEMISTS 
 
 I. BOYLE AND CAVENDISH . . 19 
 
 II. DAVY AND GRAHAM . . 41 
 
 JOSEPH BLACK: HIS LIFE AND WORK . . .67 
 
 LORD KELVIN .... 89 
 
 PIERRE EUGENE MARCELLIN BERTHELOT . 101 
 
 II. CHEMICAL ESSAYS 
 
 HOW DISCOVERIES ARE MADE . . . .115 
 
 THE BECQUEREL RAYS .' 129 
 
 WHAT IS AN ELEMENT? . . . . 147 
 ON THE PERIODIC ARRANGEMENT OF THE ELEMENTS . 161 
 
 RADIUM AND ITS PRODUCTS . . . 179 
 
 WHAT IS ELECTRICITY? ... 193 
 
 THE AURORA BOREALIS .... 205 
 
 THE FUNCTIONS OF A UNIVERSITY . 227 
 
 vii 
 
OF THE 
 
 UNIVERSITY 
 
 OF 
 
 I. HISTORICAL ESSAYS 
 
 THE EARLY DAYS OF CHEMISTRY 
 
 IN the early days of the world's history, the study of 
 science was unknown. The state of society was insecure ; 
 nation was constantly invading nation, and men had 
 little leisure for other pursuits save war and the chase. 
 Yet we find, among those nations which were sufficiently 
 powerful to resist the attacks of their neighbours, and 
 sufficiently prosperous to dispense with invasions of the 
 territory of others in quest of plunder, some attempts to 
 inquire into the mysteries of nature. In some countries, 
 as in Egypt, a leisured class of persons, the priests, urged 
 no doubt partly by a desire for knowledge, partly by a 
 wish to impress the people with a sense of their superior 
 powers, made some progress in what may be called 
 'natural philosophy/ understanding by that term 
 elementary physics and chemistry. To these they added 
 a considerable acquaintance with astronomy and mathe- 
 matics. 
 
 For practical purposes of life, too, certain of the arts, 
 notably metallurgy and dyeing, which are based on 
 chemical principles, were cultivated. But these were 
 carried on by rule of thumb, and their development was 
 slow. Indeed, they were for the most part in the hands 
 of slaves, the freemen finding it more profitable to 
 engage in commerce, or in administration. The state of 
 Turkey or Morocco, in the present day, gives a good 
 
2 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 idea of the condition of life in the centuries before the 
 Christian era, in so far as pursuit of science is concerned. 
 Even with the example of adjoining nations, whose 
 prosperity is in great part due to the attention they 
 have paid to the cultivation of scientific knowledge, the 
 Turks and the Moors display a total lack of interest. 
 Much less, then, could people such as those be expected 
 to show any eagerness in the discovery of Nature's 
 secrets. 
 
 Yet from time to time there have been minds who 
 refused to accept the daily drudgery of life as sufficient 
 for their needs. Questions such as : Whence did this 
 world arise ? What does it consist of ? What will be its 
 ultimate fate ? perplexed them, as they perplex us ; and 
 in an endeavour to answer questions like these, scientific 
 discovery was begun. Many nations, however, were 
 instructed by the priests of their religion that it is 
 impious to make such inquiries ; and it is not until the 
 era of the early Greek civilisation, when the current 
 mythology had ceased to retain its hold on abler minds, 
 that we find any serious attempt to grapple with funda- 
 mental problems like those stated. But even among the 
 Greeks we meet with a disinclination to take trouble 
 about matters which were imagined to have little if any 
 relation to human affairs; even Socrates, one of their 
 greatest thinkers, taught that it was foolish to abandon 
 those things which more nearly concern man for 
 things external to him. Plato, who chronicled the sayings 
 of Socrates, wrote in the seventh book of the Republic : 
 1 We shall pursue astronomy with the help of problems, 
 just as we pursue geometry; but if it is our desire to 
 become acquainted with the true nature of astronomy, 
 we shall let the heavenly bodies alone.' And he states 
 in another place, that even if we were to ascertain these 
 things, we could neither alter the course of the stars, 
 
THE EARLY DAYS OF CHEMISTRY 3 
 
 nor apply our knowledge so as to benefit mankind. And 
 in Timaeus, Plato remarks, ' God only has the knowledge 
 and the power which are able to combine many things 
 into one, and to dissolve the one into the many. But 
 no man either is, or ever will be, able to accomplish either 
 the one or the other operation.' 
 
 Even in the middle ages, the same spirit of content 
 with insufficient observation, and the same disposition 
 to draw conclusions from insufficient premises, is to be 
 noticed. It is difficult for us, in this age when a certain 
 acquaintance with scientific methods of thought, if not 
 with scientific facts, is common to almost every one, to 
 imagine the kind of reply to elementary questions which 
 satisfied our predecessors, even those who devoted time 
 and, one would hope, some powers of mind to a con- 
 sideration of the subject. Let us take a few examples. 
 
 The answer which one of the schoolmen would give 
 to the question : c Of what are bodies composed ? ' is thus 
 paraphrased by Le Febure, apothecary to His Majesty 
 Charles the Second : * If the substance is a body, it must 
 possess quantity ; and of necessity, it must be divisible ; 
 now, bodies must be composed either of things divisible, 
 or indivisible, that is, either of points, or of parts : a body, 
 however, cannot be composed of points, for a point is 
 indivisible, possessing no quantity, and, consequently, 
 it cannot communicate quantity to a body, since it does 
 not itself possess it. Hence it must be concluded that 
 a body must be composed of divisible parts; to this, 
 however, it may be said that such parts must either be 
 divisible or indivisible; if the former, then the part 
 cannot be the smallest possible, since it may itself be 
 divided into others still more minute ; and if this smallest 
 part is indivisible, the same difficulty confronts us, for 
 it will be without quantity, which, therefore, it cannot 
 communicate to a body, for it itself does not possess it, 
 
4 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 seeing that divisibility is the essential property of 
 quantity.' The logic is unanswerable, but we are left 
 where we were. 
 
 Let us next see what ideas were held by Du Clos, 
 physician to Louis xiv., on the cause of the solidification 
 of liquids. These are his memorable words : 
 
 ' The reason of the concretion of liquids is obviously 
 dryness ; for this quality, being the opposite of moistness, 
 which renders bodies liquid, may well produce an effect 
 opposite to that produced by the latter, to wit, the 
 concretion of liquids.' Again, we have not gained much 
 information by the profound utterance. 
 
 One more quotation. It is from a work by Jean Rey, 
 Doctor of Medicine, published in 1630, entitled, 'On an 
 Inquiry wherefore Tin and Lead increase in Weight on 
 Calcination.' He is arguing that 'Nature abhors a 
 vacuum,' a favourite thesis in former days. ' It is quite 
 certain that in the bounds of nature, a vacuum, which 
 is nothing, can find no place. There is no power in 
 Nature from which nothing could have made the universe, 
 and none which could reduce the universe to nothing : 
 that requires the same virtue. Now the matter would 
 be otherwise if there could be a vacuum. For if it could 
 be here, it could also be there ; and being here and there, 
 why not elsewhere ? and why not everywhere ? Thus the 
 universe could reach annihilation by its own forces ; but 
 to Him alone who could make it is due the glory of 
 compassing its destruction.' 
 
 We must remember, therefore, in studying the early 
 history of chemistry, that not only were facts, familiar to 
 many of us now, wholly unknown ; but we must also bear 
 in mind that the point of view from which the early 
 chemists surveyed the phenomena of nature was entirely 
 different from that to which we are now accustomed. 
 It is evident, from the examples quoted, which are not 
 
THE EARLY DAYS OF CHEMISTRY 5 
 
 taken from the writings of, those who lived at a very 
 remote time from the present day, but only six or seven 
 generations ago, that our great-great-great-grandfathers 
 differed from ourselves not merely in lack of knowledge, 
 but in the way they regarded the facts which they 
 observed. And it is consequently somewhat difficult for 
 us to adopt their point of view, and to think their 
 thoughts. But we must attempt to do so, if we are to 
 realise the progress of our science. 
 
 The progress of the science of Chemistry, indeed, forms 
 one phase of the progress of human thought. The ideas 
 which have been held, however, run in certain channels. 
 They may all be referred to speculations on the nature 
 of matter ; but the speculations take different forms. 
 For it may be inquired : What forms is matter capable of 
 assuming ? Or, what is the minute structure of matter ? 
 Or, what changes does matter undergo ? These three 
 questions were for the ancients, as they are still for us, 
 fundamental; and it will be the aim of these essays to 
 endeavour to give the reader some idea of the history 
 of these three lines of thought. We shall see that 
 our present knowledge enables us in some measure 
 to connect these three lines of inquiry by virtue of 
 certain hypotheses ; but it will be convenient to treat 
 of each separately, at least up to a certain stage. 
 
 THE ELEMENTS 
 
 The word 'Element/ in the old days, had a meaning 
 different from that which we now ascribe to it ; or, to be 
 more exact, it had two meanings, which were frequently 
 confounded with one another. The suggested derivation 
 of the word indicates one of these meanings ; it is that 
 which we usually give it ; for, just as ' 1,' ' m,' and ' n ' are 
 
6 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 constituents of the alphabet, so an ' element ' was regarded 
 as a constituent of substances. From the use of the 
 word by ancient authors, however, it would appear that 
 an element was often regarded as a property of matter ; 
 and it was evidently supposed that by changing the 
 properties, or in the words of the old writers adding more 
 or less of one or other element to a substance, the 
 substance itself could be transmuted into another wholly 
 different. We shall see examples of the two meanings 
 illustrated later on. 
 
 It is probable that the original ideas of elements 
 reached Greece from India. The Buddhistic teaching 
 was that the elements are six in number, namely, Earth, 
 Water, Air, Fire, Ether, and Consciousness. But they are 
 given by Empedocles of Agrigent, who lived about 440 
 B.C., without, the two last; and many disputes arose as 
 to which was to be regarded as the primary one, from 
 which all the others were derived ; for even at that 
 remote date, speculation was rife as to the unity of 
 matter. While Thales contended that the original 
 element was water, Anaximenes believed it to be air or 
 fire; and Aristotle did not regard elements as different 
 kinds of matter, but as different properties appertaining 
 to one original matter. Plato, however, evidently con- 
 sidered elements to be different kinds of matter, for he 
 puts these words into the mouth of Timaeus : 'In the 
 first place, that which we are now calling water, when 
 congealed, becomes stone and earth, as our sight seems 
 to show us [here he refers probably to rock-crystal, then 
 supposed to be petrified ice] ; and this same element, 
 when melted and dispersed, passes into vapour and fire. 
 Air, again, when burnt up, becomes fire, and again fire, 
 when condensed and extinguished, passes once more 
 into the form of air ; and once more air, when collected 
 and condensed, produces cloud and vapour; and from 
 
THE EARLY DAYS OF CHEMISTRY 7 
 
 these, when still more compressed, comes flowing water ; 
 and from water come earth and stones once more; and 
 thus generation seems to be transmitted from one to the 
 other in a circle.' 
 
 Aristotle attributed to these elements four properties, of 
 which each possessed two. Thus, Earth was cold and 
 dry ; Water, cold and moist ; Air, hot and moist ; and 
 Fire, hot and dry. A fifth element was also conceived by 
 Aristotle to accompany these four; he termed it V\TJ, 
 translated into the Latin Quinta Essentia ; and this was 
 regarded by alchemists of a later date as of the utmost 
 importance, for it was supposed to penetrate the whole 
 world. The ceaseless strivings of the alchemists after 
 the 'quintessence' were due to the notion that, were it 
 discovered, all transmutations would then be possible. 
 Yet the word ' Chemistry' was not, so far as we know, in use 
 in Aristotle's time. It is said to occur in a Greek manu- 
 script of Zosimus, a resident in Panapolis, a city in Egypt, 
 who wrote in the fifth century. It appeared to mean the 
 art of making gold and silver ; for the title of his work is 
 given by Scaliger as * A faithful Description of the sacred 
 and divine Art of making gold and silver.' M. Berthelot, 
 who has made a detailed study of ancient Greek, Arabic, 
 Syriac, and Latin manuscripts relating to early chemistry, 
 believes that the attempts to transmute metals arose, not 
 from any philosophical notions regarding the nature of 
 elements, but from fraudulent attempts of goldsmiths to 
 pass off base metals on their customers for silver and 
 gold. One of the earliest manuscripts on record dates 
 from the third century, and is preserved at Leiden in 
 Holland. It was found in a tomb in Thebes in 1828. 
 It is a rough and ill-spelt collection of workman's receipts 
 for working in metals, in which frequent reference is 
 made to an alloy of copper and tin an alloy which in 
 many respects resembles gold. It is apparently a manu- 
 
8 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 script which escaped the fate of most of the Egyptian MSS. 
 of that date; for about the year 290, the Emperor 
 Diocletian commanded that all works on alchemy should 
 be burnt, * in order that the Egyptians might not become 
 rich by the art [of making gold and silver] and use their 
 wealth to revolt against the Romans.' 
 
 But although the idea of transmutation did not arise 
 from such theoretical speculations as Aristotle's on the 
 unity of matter, and on the possibility of converting one 
 kind of matter into another by altering its properties, 
 or in the language of the time, adding or removing more 
 or less of one or other element, yet the later workers did 
 not scruple to use Aristotle's theory in order to make 
 good their case. And for many centuries indeed until 
 our own time there have always existed men who 
 devoted their lives to this object. 
 
 There was, at the same time, a supposed mystical 
 connection, of Chaldean origin, between the metals and 
 the planets. Thus gold was the sun ; silver, the moon ; 
 copper, Venus ; tin, and afterwards mercury, was associ- 
 ated with the planet of that name ; iron, used in battle, 
 had affinity with ruddy Mars ; electron, an alloy of gold 
 and silver, and subsequently tin, was Jupiter ; and sluggish 
 and heavy lead was the slow-moving Saturn. These 
 analogies were used in casting horoscopes, or predicting 
 the future of those rich and credulous enough to consult 
 astrologers. 
 
 At the same time as these fantastic notions were held, 
 many processes of manufacture, involving a knowledge 
 of chemical reactions, were carried on. These will be 
 alluded to later ; but it may be noted here that speculation 
 did not take the course of attempting to devise explana- 
 tions of chemical changes, but was indulged in, as 
 before remarked, with little reference to experimental 
 methods. 
 
THE EARLY DAYS OF CHEMISTRY 9 
 
 The conquest of Egypt by the Arabians in the seventh 
 century put an end for a time to the school of learning 
 of Alexandria, where citizens of all nations met and dis- 
 cussed problems of all kinds. But the spirit of the Grseco- 
 Egyptians was too strong even for the fanaticism of the 
 Arabians ; the conquered became the conqueror ; and an 
 Arabian school of philosophy arose, which carried on the 
 traditions acquired from the Greeks. It has been be- 
 lieved, until M. Berthelot showed the belief to be erro- 
 neous, that Latin works which professed to be translations 
 from the Arabic of the eighth and succeeding centuries 
 were really renderings of the ancient Arabian authors. 
 It appears, however, that they are for the most part 
 forgeries, having little if any resemblance to the originals. 
 Thus Geber, said to have been translated into Latin in 
 1529, is entirely different from the Arabic writings of the 
 real Geber. The historical Geber lived in the ninth cen- 
 tury. His comment on alchemy is characterised by 
 strong common sense. It is : 'I saw that persons em- 
 ployed in attempts to fabricate gold and silver were 
 working in ignorance, and by false methods ; I then per- 
 ceived that they belonged to two classes, the dupers and 
 the duped. I pitied both of them.' 
 
 About this time, however, an addition to Aristotle's 
 classification of elements was made ; and it endured until 
 within the last two hundred years. It evidently arose 
 from attempts to account for the properties of the metals, 
 and the changes which they undergo by heat. These 
 additional 'principles,' as they were termed, were salt, 
 sulphur, and mercury. We read that the noble metals 
 contain 'a very pure mercury/ the meaning being, pro- 
 bably, that they possess a high metallic lustre ; while the 
 common metals, such as copper and iron, contain ' a base 
 sulphur,' implying that these metals are easily altered by 
 fire, losing their metallic appearance and changing into 
 
10 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 black scales. These principles were later increased to 
 five, by the addition of ' phlegm ' and of ' earth.' Fanci- 
 ful analogies were drawn between the Divine Trinity of 
 Father, Son, and Holy Spirit, the human Body, Soul, 
 and Spirit, and the three principles above-named. At- 
 tempts were incessantly made to draw inspiration from 
 such impossible fancies. Thus the volatilisation of mer- 
 cury, or ' Spirit ' as it was sometimes called, was deemed 
 analogous to the ascension of Christ! In fact, there is 
 no limit to the absurdity and folly of the endeavours of 
 the alchemists. Let us hear a list of their processes, as 
 told by Sir George Ripley, who lived and wrote in 1471. 
 
 c The fyrst Chapter shalbe of naturall Calcination ; 
 The second of Dyssolution secret and phylosophycall ; 
 The third of our Elemental Separation ; 
 The fourth of Conjunction matrymonyall ; 
 The fifth of Putrefaction then folio we shall ; 
 Of Congelatyon, albyfycative shall be the Syxt, 
 Then of Cybation the seaventh shall follow next. 
 The secret of our Sublymation the eyght shall show ; 
 The nynth shall be of Fermentation ; 
 The tenth of our Exaltation I trow ; 
 The eleventh of our mervelose Multyplycatyon ; 
 The twelfth of Projectyon, then Recapytulatyon ; 
 And so thys treatise shall take an end, 
 By the help of God, as I entend.' 
 
 These chapters are wearisome and rambling ; and it is 
 impossible to gain a single clear idea from their perusal. 
 Indeed it was part of the creed of the alchemists that 
 their secrets were too precious to be revealed to the baser 
 sort of men. 
 
 1 The Philosophers were y-sworne eche one 
 That they shulde discover it unto none, 
 He in no boke it write in no manere 
 For unto Christ it is so lefe and deare : 
 
THE EARLY DAYS OF CHEMISTRY 11 
 
 That he wol not that it discovered be, 
 But where it liketh to his deite : 
 Man to inspire and eke for to defend 
 Whan that him liketh : in this is his end ' 
 
 sang Chaucer, and he told a true tale, for the meanings of 
 alchemical expressions are often undecipherable. 
 
 The green lion, the basilisk, the cockatrice, the sala- 
 mander, the flying eagle, the toad, the dragon's tail and 
 blood, the spotted panther, the crow's bill, blue as lead, 
 kings and queens, red bridegrooms and lily brides, and 
 many more mystical terms which had no doubt some 
 meaning to adepts, were mingled in inextricable con- 
 fusion. 
 
 Moreover, the alchemists made use, not only of fantastic 
 expressions, in order to preserve their supposed secrets 
 from the common people, but they had also a set of 
 symbols, possibly originating from the Chaldean or Egyp- 
 tian alphabets, by which the substances and many of the 
 processes used were symbolised. While the chief aim of 
 modern science is perspicuity, that of the alchemists was 
 ambiguity and mystery. In many cases they were so 
 successful in preserving their secrets that even modern 
 investigation has failed to reveal them. But there is one 
 grain of comfort, albeit it savours of sour grapes, it is 
 perfectly certain that there was nothing worth revealing ; 
 at least nothing which it could profit a modern student 
 of science to know. Where the descriptions have been 
 interpreted, they refer to imperfect methods of doing 
 what we are now able to do with much greater economy 
 and rapidity. As already pointed out, their theory of 
 elements was erroneous ; they were, moreover, acquainted 
 with very few pure substances, and had no criterion of 
 the purity of those they possessed ; and they failed to 
 realise the existence of gases as forms of matter. 
 
12 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Yet the interminable experiments which were con- 
 ducted with a view of discovering the ' Philosopher's 
 Stone/ which should convert the baser metals into gold, 
 and the elixir vitce, which should convey undying youth 
 on its happy possessor, led to the discovery of many 
 chemical compounds. The writings of Basil Valentine, 
 reputed to have been a Benedictine monk living in South 
 Germany during the latter half of the fifteenth century, 
 contain a description of many substances, now known 
 as chemical entities, together with the methods of pre- 
 paring them. In a tract entitled ' The Great Stone of the 
 Ancients/ he gives in detail the properties of ordinary 
 sulphur; of mercury, alluding to the medicinal uses of 
 its compounds ; of antimony oxide or ' Spiessglas/ which 
 he conjectures to consist of 'much mercury, also much 
 sulphur, though little salt ' ; of copper- water, or a solution 
 of copper sulphate ; of lima potabilis or solution of silver 
 nitrate; of quick-lime; of arsenious oxide; of saltpetre. 
 The last he makes tell its own story : ' Two elements are 
 found in me, in quantity fire and air ; I contain water and 
 earth in less amount ; therefore am I fiery, burning, and 
 volatile. For a subtle spirit resides in me ; I am likest to 
 mercury inwardly hot but outwardly cold. My chief 
 enemy is common sulphur; and yet he is my greatest 
 friend, for I am purified and refined through him.' Sal- 
 ammoniac, tartar, vinegar, and above all, numerous com- 
 pounds of antimony were also described by Basil Valen- 
 tine, the last in his celebrated work entitled, The Trium- 
 phal Chariot of Antimony. In his writings, however, 
 he points out that many of the substances he describes 
 have medicinal properties ; and his successors, of whom 
 perhaps the best known was Paracelsus, developed this 
 part of his teaching. Yet in spite of his considerable 
 knowledge, he retained belief in transmutation : he also 
 added one to the previously received two principles of 
 
THE EARLY DAYS OF CHEMISTRY 13 
 
 Geber and his disciples, namely salt, or, as he terms it, 
 ' salt of the philosophers ' ; it is the constituent of matter, 
 which confers solidity, and which remains after the volatile 
 mercury and sulphur have been removed by heat. 
 
 In the first half of the sixteenth century Paracelsus 
 extended and applied the suggestion of Basil Valentine, 
 and founded what became known as the school of ' iatro- 
 chemists' a body of men who taught that the chief 
 object of chemistry is not the transmutation of metals, 
 but the application of chemical substances to medical 
 uses. He adhered, however, to Valentine's theory of the 
 three principles ; but he applied them to the human 
 body, teaching that the organism itself consists of these 
 principles, and that disease, owing its origin to a deficiency 
 of one of them, is to be combated by its being restored 
 to the system. Increase of sulphur, he taught, gives rise 
 to fever and the plague ; increase of mercury to paralysis 
 and depression ; and of salt, to diarrhoea and dropsy. Too 
 little sulphur in the organism produces gout ; delirium is 
 caused by distilling it from one organ to another, and so 
 on in fanciful theorisings. One of the most fantastic is his 
 attributing the nutrition of the body to a beneficent spirit, 
 named the ' Archseus,' who resided in the stomach, and 
 presided over the function of digestion. But these 
 curious notions have little bearing on the development 
 of chemistry. The teaching of Paracelsus, however, had 
 the good effect of directing attention to an important 
 branch of chemistry its use in pharmacy. And from 
 his time onwards, indeed, up to the middle of last cen- 
 tury, many of the best-known chemists had received a 
 medical training, and the ranks of chemical investigators 
 were largely recruited from the medical profession. 
 
 Although the alchemists, after the beginning of the 
 seventeenth century, exercised little influence on the 
 progress of chemistry, they continued their fruitless 
 
14 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 quest. The possibility of transmutation has always been 
 associated with speculations concerning the unity of 
 matter. And although there is little evidence as yet to 
 justify the supposition that all substances are ultimately 
 composed of matter of one kind, still the history of our 
 science contains many accounts of attempts to effect 
 transmutation. One such attempt, in modern times, was 
 made by Dr. Samuel Brown, who claimed to have obtained 
 silicon from paracyanogen, a compound consisting of car- 
 bon and nitrogen alone; but subsequent workers failed 
 to substantiate his results. There is, however, no ques- 
 tion as regards the honesty of Dr. Brown's work; the 
 only conclusion is that he must have omitted to take 
 sufficient precautions against contamination of his carbon 
 compounds with silicon. There exist at present in France 
 also secret societies, with such titles as 'L'Ordre de la 
 Rose-Croix,' and ' L' Association alchimique de France,' 
 the latter the successor of one named 'La Societe Her- 
 metique.' One of the latest of their 'researches' was 
 carried out by ' Maitre ' Theodore Tiffereau ; he professed 
 in 1896 to have obtained compounds of carbon ether 
 and acetic acid from the metal aluminium, sealed up 
 with nitric acid in a glass tube, and exposed to the sun's 
 rays for two months. But the attempt to transmute 
 baser materials into gold still holds the field. August 
 Strindberg claims to have produced ' incomplete ' gold 
 from ferrous ammonium sulphate ; and still more recently 
 Emmens, who, however, disclaims the name of alchemist, 
 states that he has converted Mexican silver dollars into 
 gold, or more correctly, increased the small amount of 
 gold actually present in such coins, by hammering the 
 metal exposed to an extremely low temperature. There 
 is reason to suspect the existence of an element which 
 should resemble both gold and silver ; Emmens pro- 
 fesses to have made this element, which he names 
 
THE EARLY DAYS OF CHEMISTRY 15 
 
 argentaurum, by hammering silver, and to have trans- 
 muted it, by a further process, into gold. He claims, 
 too, that Sir William Crookes has obtained proof, slight 
 it is true, though decisive, of an increase in the quantity 
 of gold in a Mexican dollar, after treating the latter by 
 his process. 
 
 We have seen from what precedes that the doctrine 
 concerning elements, held from remote times, was that 
 they were four in number, earth, water, air, and fire. 
 That besides these, there exist three chemical or ' hypo- 
 static ' principles, to wit, sulphur, mercury, and salt. In 
 spite of the refutation of such views by the Honourable 
 Robert Boyle, which we shall consider later, they lingered 
 on until the middle of last century, being quoted in 
 almost all treatises on chemistry. Macquer's Chemistry, 
 a text-book which obtained a wide circulation in its day, 
 gives the following description of the ancient elements 
 (1768): 'Air is the fluid which we constantly breathe, 
 and which surrounds the whole surface of the terrestrial 
 globe. Being heavy, like all other bodies, it penetrates 
 into all places that are not either absolutely inaccessible 
 or filled with some other body heavier than itself. Its 
 principal property is to be susceptible of condensation 
 and rarefaction; so that the very same quantity of Air 
 may occupy a much greater or a much smaller space, 
 according to the different state it is in. Heat and cold, or, 
 if you will, the presence or absence of the particles of Fire, 
 are the most usual causes, and indeed, the measure of its 
 condensation and rarefaction : for, if a certain quantity of 
 air be heated, its bulk increases proportionately to the 
 degree of heat applied to it ; the consequence of which is, 
 that the same space now contains fewer particles than 
 it did before.' ' Air enters into the composition of many 
 substances, especially vegetable and animal bodies ; fully 
 analysing most of them, such a considerable quantity 
 
16 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 thereof is extricated, that some naturalists have suspected 
 it to be altogether destitute of elasticity, when thus 
 combined with other principles in the composition of 
 bodies.' 
 
 After describing some of the physical properties of 
 water, Macquer continues : ' Water enters into the texture 
 of many bodies, both compounds and secondary principles ; 
 but, like air, it seems to be excluded from the composi- 
 tion of all metals and most minerals. For although an 
 immense quantity of water exists in the bowels of the 
 earth, moistening all its contents, it cannot be thence 
 inferred that it is one of the principles of minerals. It 
 is only interposed between their parts ; for they may be 
 entirely divested of it, without any sign of decomposition : 
 indeed, it is not capable of an intimate connection with 
 them.' 
 
 Of earth he says : ' We observed that the two principles 
 above treated of are volatile ; that is, the action of fire 
 separates them from the bodies they help to compose, 
 carrying them quite off and dissipating them. That of 
 which we are now to speak, namely earth, is fixed, and 
 when it is absolutely pure, resists the utmost force of fire. 
 So that, whatever remains of a body, after it has been 
 exposed to the power of the fiercest fire, must be con- 
 sidered as containing nearly all earthy principle, and 
 consisting chiefly thereof.' ' Earth, therefore, properly so 
 called, is a fixed principle which is permanent in the fire.' 
 He then goes on to distinguish between fusible or vitrifi- 
 able earths, and infusible or unvitrifiable earths, the latter 
 of which are also called absorbent earths, from their pro- 
 perty of imbibing water. 
 
 Maquer's views regarding fire are as follows : ' The matter 
 of the sun, or of light, the Phlogiston, fire, the sulphureous 
 principle, the inflammable matter, are all of them names 
 by which the element of fire is usually denoted. But it 
 
THE EARLY DAYS OF CHEMISTRY 17 
 
 should seem that an accurate distinction has not been 
 made between the different states in which it exists ; that 
 is, between the phenomena of fire actually existing as a 
 principle in the composition of bodies, and those which 
 it exhibits when existing separately, and in its natural 
 state : nor have proper distinct appellations been assigned 
 to it in these different circumstances. In the latter state, 
 we may properly give it the names of fire, matter of the 
 sun, of light, and of heat ; and may consider it as a sub- 
 stance composed of infinitely small particles, continually 
 agitated by a most rapid motion, and of consequence essen- 
 tially fluid.' ' The greatest change produced on bodies, 
 by its presence or its absence, is the rendering them 
 fluid or solid; so that all other bodies may be deemed 
 essentially solid; fire alone essentially fluid, and the 
 principle of fluidity in others. This being presupposed, 
 air itself might become solid, if it could be entirely de- 
 prived of the fire it contains ; as bodies of most difficult 
 fusion become fluid, when penetrated by a sufficient 
 quantity of the particles of fire.' 
 
 An attempt has been made in the preceding pages to 
 show the manner in which the world around us was 
 regarded. People were content to take as true what they 
 were told ; in fact, it was regarded as unfitting that the 
 ' mysteries ' with which we are surrounded should be too 
 minutely inquired into. Great reverence was paid to 
 tradition; and more attention to the celebrity and per- 
 sonal character of those who advocated certain dogmas 
 than to the evidence in favour of their intrinsic probability. 
 
 This spirit is by no means extinct; the vast majority 
 of the human race are content to gain knowledge at 
 second hand. Whether such knowledge is worth having 
 may well be questioned; it is of course impossible that 
 every man should investigate natural phenomena for 
 himself ; but it is at least possible to place every child in 
 
 B 
 
18 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 the position of knowing, in however elementary a way, 
 how useful deductions have been drawn from observa- 
 tion and experiment, and of emancipating himself, to 
 some extent at least, from the thraldom of intellectual 
 authority. 
 
THE GREAT LONDON CHEMISTS 
 
 I. BOYLE AND CAVENDISH 
 
 THE country which is in advance of the rest of the world 
 in Chemistry will also be foremost in wealth and in 
 general prosperity. For the study of Chemistry is so 
 closely bound up with our development in all kinds of 
 industry, with the arrestment of disease, and with our 
 success in war, that it is essential to a wealthy, healthy, 
 and peaceful nation. The electrician is dependent on 
 the chemist for the iron suitable for his dynamos; the 
 engineer, for the materials which he uses in his con- 
 struction ; and the scouring, bleaching, and dyeing of the 
 fabrics with which we are clothed, the manufacture of 
 the paper on which we write, and the ink with which we 
 soil the paper ; the provision of our food-supply, and 
 the removal of effete matter from our houses; the 
 preparation of our medicines; and the synthesis of the 
 high explosives with which warfare is now conducted ; 
 all these belong to the domain of the chemist, and 
 without them we should lapse into the. semi-barbarism 
 of our ancestors. 
 
 Still, it must be borne in mind that we are far from 
 perfection. No process is so perfect that there is not 
 plenty of room for improvement. There is no finality 
 in science. And that which to-day is a scientific toy 
 may be to-morrow the essential part of an important 
 industry. This is one, though not in my view the most 
 important, inducement to study the science of Chemistry. 
 
 19 
 
20 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 To extend the bounds of human knowledge, and in so 
 doing to glorify our Creator, is surely still more an end 
 to be striven after. To quote from the words of Francis 
 Bacon, prefixed by Charles Darwin to his Origin of 
 Species: 'To conclude, therefore, let no man, out of a 
 weak conceit of sobriety or an ill-applied moderation, 
 think or maintain that a man can search too far, or be 
 too well studied in the book of God's -words, or in the 
 book of God's works, divinity, or philosophy ; but rather 
 let men endeavour an endless progress or proficience in 
 both.' Yet the acquisition of wealth and fame will pro- 
 bably now, as it has in the past, appeal more forcibly to 
 the mind of the ordinary man ; and we must not despise 
 any inducement, which will lead to the furtherance of 
 the object to be gained, provided the motives are not in 
 themselves sordid. 
 
 The study of science, with the express object of securing 
 wealth and fame, is not likely to secure either. The old 
 story of the desire of King Solomon is often fulfilled in 
 our day. Solomon's request was, ' Give me now wisdom 
 and knowledge ' ; and he was answered, ' Wisdom and 
 knowledge is granted unto thee, and I will give thee 
 riches and wealth and honour.' The reason why an 
 attempt to utilise science for the attainment of wealth 
 often fails is a simple one. It is due to the unfortunate 
 circumstance that the human mind is not omniscient. 
 No man, beginning a research, can know to what it will 
 ultimately lead. It will certainly, if rightly pursued, 
 lead to knowledge ; but whether it will bring riches and 
 fame is beyond his ken. There have been, however, 
 researches expressly directed to some specific object, 
 which have succeeded in their purpose; and we shall 
 see later how the discovery of principles which led to 
 the invention of the safety-lamp by Sir Humphry Davy 
 illustrates this. But as a rule, those chemists who have 
 
THE GREAT LONDON CHEMISTS 21 
 
 achieved for themselves immortal fame have striven 
 after the nobler goal the increase of the sum of human 
 knowledge. It is to the lives of some of those, who have 
 been more or less connected with London, that I ask your 
 attention. May those of us who follow, at however -far a 
 distance, profit by their example ! 
 
 In the olden days, science, as we know it now, was 
 non-existent. The minds of most men who were free 
 from the thraldom of incessant labour were occupied 
 with war or statecraft as a business, and with the chase 
 as a recreation. Those to whom such pursuits, from 
 circumstances or mental habit, were repugnant, found 
 occupation in history, poetry, philosophical discussion, 
 or religion. It is true, speculation on the nature of the 
 world around them was indulged in by some; but they 
 were guided in their views by their opinion rather of what 
 ought to be, than what is. The attitude of the modern 
 mind is more humble. We no longer believe that we 
 share enough of the creative power to enable us to 
 construct a system of the universe; we are content if 
 we are able, in however modest a way, to interpret 
 nature, and we call to our aid experiment, as a means of 
 questioning nature. We are prompt in communicating 
 our knowledge to others, and we expect their aid and 
 look for their criticism. In former days, the language 
 of mystery was employed. It concealed secrets too 
 precious to be laid bare to the vulgar crowd. ' In those 
 days/ to quote the words of Dr. Samuel Brown, 1 'the 
 metals were suns and moons, kings and queens, red 
 bridegrooms and lily brides. Gold was Apollo, " sun of 
 the lofty dome"; silver, Diana, the fair moon of his 
 unresting career, and chased him meekly through the 
 celestial grove ; quicksilver was the wing-footed Mercury, 
 
 1 Dr. Samuel Brown's Essays. 
 
22 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Herald of the Gods, "new-lighted on a heaven-kissing 
 hill " ; iron was the ruddy-eyed Mars, in panoply complete ; 
 lead was heavy-lidded Saturn, " quiet as a stone," within 
 the tangled forest of material forms ; tin was the Diabolus 
 Metallorum, a very devil among the metals, and so forth 
 in not unmeaning mystery. 
 
 ' There were flying birds, green dragons, and red lions. 
 There were virginal fountains, royal baths, and waters of 
 life. There were salts of wisdom, and essential spirits so 
 fine and volatile, that drop after drop, let fall from the 
 lip of the wonderful phial that contained them, could 
 never reach the ground. There was the powder of 
 attraction which drew all men and women after its 
 fortunate possessor ; and the alcahest, or universal solvent 
 and noli-me-tangere of essences. There was the grand 
 elixir that conferred undying youth on the glorious 
 mortal who was pure and brave enough to kiss and 
 quaff the golden wavelet as it mantled o'er the cup of 
 life the fortunate Endymion of a new mythology. There 
 were the Philosophical stone, and the Philosopher's stone ; 
 the former the art and practice, the latter the theory 
 and idea, of turning baser natures into nobler ; the theory 
 and practice of exaltation. The Philosophical stone was 
 younger than the elements, yet at her virgin touch the 
 grossest calx among them all would blush before her into 
 perfect gold. The Philosopher's stone was the first-born 
 of all things, and older than the king of metals. In a 
 word, there was an interminable imbroglio of a few of 
 the hard-won facts of nature, a multitude of traditionary 
 processes and results, several very just analogies, some 
 most fantastical notions, one or two profound, but intract- 
 able ideas, a haze of philosophical mysticism, and an 
 under-current of fervid religiosity.' 
 
 Such conceptions ruled the minds of philosophers, as 
 they loved to call themselves, until the middle of the 
 
THE GREAT LONDON CHEMISTS 23 
 
 seventeenth century. But the practice of interrogating 
 nature by experiment had sprung up, and was soon 
 destined to bear good fruit. Although these notions of 
 matter and its elementary forms lingered on until a much 
 later date, and indeed are not wholly extinct at the present 
 day, they received their first great blow about this time ; 
 the first brunt of an attack which was destined ultimately 
 to overthrow them. 
 
 This attack was made by Boyle. The spirit in which 
 he approached the hostile ranks is best given in his own 
 words: 'For I am wont to judge of opinions, as of coins; 
 I consider much less in any one that I am to receive 
 whose inscription it bears, than what metal 'tis made of. 
 'Tis indifferent enough to me whether 'twas stamped 
 many years or ages since, or came but yesterday from 
 the mint. Nor do I regard how many or how few hands 
 it has passed through, provided I know by the touchstone 
 whether or no it be genuine, and does or does not deserve 
 to have been current. For if, upon due proof, it appears 
 to be good, its having been long and by many received 
 for such will not tempt me to refuse it ; but if I find it 
 counterfeit, neither the Prince's image nor superscription, 
 nor its date, nor the multitude of hands it has passed 
 through, will engage me to receive it. And one dis- 
 favouring trial, well made, will much more discredit it 
 with me, than all those spurious things I have named 
 can recommend it.' 
 
 In this spirit the ' Sceptical Chymist, or considerations 
 upon the experiments usually produced in favour of 
 the four elements, and of the three chymical principles 
 of the mixed bodies' was written. In it, the various 
 theories of matter, which, like a river rising in the 
 remotest recesses of time had gathered tributaries as it 
 flowed and presented a formidable flood in Boyle's days, 
 were searchingly criticised. Every postulate was examined ; 
 
24 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 if possible, experimentally tested; if true, kept; if false, 
 rejected. 
 
 Thus, early in the book, we meet with the phrase, long 
 accepted as true, ffomogenea congregare ; that is, 'Like 
 draws to like.' This Boyle disproved by showing that 
 liquids, like alcohol and water, alike in being colourless 
 and transparent, although they mix with each other, may 
 be easily separated by freezing; for, when cooled, the 
 water freezes, leaving the alcohol unfrozen. Here we find 
 the first record of experiments on a subject which, in 
 Raoult's hands, yielded such extraordinarily important 
 results. Another of Boyle's arguments is, that although 
 liquids and gases mix respectively with each other, yet 
 solids show no such tendency, and do not even cohere, 
 except in cases where the cohesion can be explained 
 by the form of the solid, and the consequent exertion of 
 atmospheric pressure. 
 
 After making a number of such attacks, Boyle proceeds 
 to consider the hypothesis at that time all-prevalent and 
 universally accepted, of the elements salt, sulphur, and 
 mercury. He opens two distinct lines of attack. His 
 first may be stated thus : If all substances are composed 
 of salt, sulphur, and mercury, and if vegetable and animal 
 substances contain, as is stated, much mercury, little 
 sulphur, and less salt, then it is desirable to show that a 
 vegetable may be constructed of a substance containing 
 none of these principles, but only of water, which was 
 then sometimes termed ' phlegm/ and was ranked among 
 the elements. This he attempted by growing a ' pompion ' 
 in a weighed quantity of earth, and after the pumpkin 
 had grown, he showed it to consist of water, by distilling 
 it ; and by weighing the earth, he proved that it had not 
 lost weight. He then turns to the c vulgar spagyrist/ and 
 triumphantly challenges the truth of his theory. It is 
 now known that the elements carbon and nitrogen, and 
 
THE GREAT LONDON CHEMISTS 25 
 
 others in small quantity, must be added to those contained 
 in water to produce a ' pompion ' ; but it was a great step 
 to show that no salt, sulphur, or mercury were necessary. 
 Boyle viewed the ' pompion ' as simply transmuted water. 
 He quotes from M. de Roche, who stated that he had 
 transmuted earth into water, and vice versa. Of the 
 correctness of M. de Roche's opinion, he is not quite 
 sure, but he attaches a certain amount of weight to it. 
 
 His second line of attack is to prove that the so-called 
 elements are themselves further resolvable. And begin- 
 ning with sulphur, he points out that what the chymists 
 understand by sulphur has not always the same properties. 
 It is, however, always inflammable. Sulphur, in the then 
 accepted meaning of the word, was the inflammable 
 portion obtained on distilling an animal or vegetable 
 substance; mercury, another portion, not miscible with 
 the sulphur; but uninflammable, and having taste; the 
 residue on incineration, or, as it was termed, the caput 
 mortuum, was salt. In an old writing on the subject, 
 salt is said to be the basis of solidity and permanency 
 in compound bodies ; oil or sulphur (the two words came 
 to have nearly the same meaning) serves the purpose of 
 making the mass more tenacious ; mercury is to leaven 
 and to promote the ingredients, and earth is to soak and 
 dry up the water in which the salt is dissolved. 
 
 We note here a change in the manner of regarding 
 elements. They are no longer principles, or abstract 
 qualities of matter, but they exist in the matter, and can 
 be extracted from it by suitable processes. Their number 
 varied ; and phlegm or water was now accepted as elemen- 
 tary, now rejected, as suited the purpose of the theorist. 
 Boyle clearly showed that these elements had not always 
 the same properties; that the sulphur and mercury not 
 only differed in every respect from brimstone and quick- 
 silver, but that one variety, obtained by distilling wood, 
 
26 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 differed from that obtained by submitting bones to the 
 same process. He clinched his point by distilling the 
 distillates themselves in turn in fact by performing what 
 we now call a ' fractional distillation ' and showed that 
 it was possible to divide them in turn into several liquids, 
 differing from each other in properties. In this he antici- 
 pated a process now practised on a very large scale, namely 
 the manufacture of vinegar from wood, which he success- 
 fully separated from wood-spirit and tar. 
 
 Almost all research, before Boyle's time, employed two 
 processes, ignition or heating in contact with air, and dis- 
 tillation, or heating in a vessel of irregular shape, named 
 an alembic, leading the vapours through a cooled tube, 
 still called a worm, and collecting the liquefied product in 
 a pear-shaped vessel, named a receiver. Heat was assumed 
 to be the universal resolver of bodies ; and the products 
 of the action of heat on compounds were accepted as 
 elements. Boyle doubted this; he questioned whether 
 the products obtained on distillation were pre-existent in 
 the substances distilled, as the theory of elements would 
 require. He found that on distillation the same substances 
 are not always produced, nor the same number ; and he 
 demonstrated that these products themselves are not pure 
 or elementary bodies, but ' mixts.' He says : ' It is to be 
 doubted whether or no there be any determinate number 
 of elements, or if you please, whether all compound bodies 
 do consist of the same number of elementary principles 
 or ingredients.' 
 
 But Boyle was not merely a destroyer ; he also, if not 
 in so orderly a manner, attempted to construct a theory 
 of his own. He appears to have held the notion of a 
 universal matter, and to have conceived the different 
 varieties to be due, not to the presence of separable pro- 
 perties, but to the form and motion of its minute portions. 
 In supporting this doctrine against the theories prevalent 
 
THE GREAT LONDON CHEMISTS 27 
 
 in his time, he says : ' I demand also, from which of the 
 chymical principles motion flows, which yet is an affection 
 of matter much more general than can be deduced from 
 any of the three chymical principles.' In an essay entitled 
 ' The history of Fluidity and Firmness,' he endeavours with 
 some success to show that all bodies, even those which 
 appear most rigid, are in motion. For example, he points 
 out that the diamond when rubbed shines in the dark, 
 and in conformity with our present views, attributes that 
 to molecular motion. He also notices that all bodies ex- 
 pand by heat, and is inclined to ascribe the magnetisation 
 of steel to the motion of its minute particles. He attri- 
 butes the varying properties of matter to motion and 
 rest. In yet another passage, he supposes the action of 
 acids on metals to be due to the pointed shape of their 
 atoms, which, by inserting themselves between the more 
 rounded particles of the metal, wedge them asunder, and 
 themselves become blunt during the process. 
 
 It is difficult to overestimate the value of Boyle's 
 labours in the field of chemistry. Although he was the 
 first to proclaim that chemistry is independent of any art, 
 and must be regarded as part of the great field of nature, 
 yet the practical benefit which has accrued to mankind 
 through Boyle's theoretical as well as his practical work 
 is incalculable. It was not until after his time that it 
 was possible to construct a theory explaining the rule-of- 
 thumb methods of manufacture which were formerly 
 employed, and to render improvement and discovery no 
 longer a matter of chance, but of reasoning. The whole 
 progress of modern manufacture due to the elaboration 
 of scientific discoveries, themselves the result, not of hap- 
 hazard trial, but of careful and systematic investigation, 
 sufficiently attests the benefit conferred by him in the 
 practical application of scientific principles. 
 
 Time would fail to tell of Boyle's well-known memoir 
 
28 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 ' Touching the Spring of the Air/ in which he describes 
 experiments proving that a volume of air under a pressure 
 of two pounds occupies exactly half the volume that it 
 does under a pressure of one pound. This, although not 
 absolutely true, is yet sufficiently exact to be generalised 
 into a law, which is known by Boyle's name. He finds a 
 reason for this ' spring ' in premising that ' the air abounds 
 in elastic particles, which being pressed together by their 
 own weight constantly endeavour to expand and free 
 themselves from that force ; as wool, for example, resists 
 the hand that squeezes it, and contracts its dimensions ; 
 but recovers them when the hand opens, and endeavours 
 at it even while that is shut.' 
 
 In truth Boyle delighted in mechanical explanations. 
 The titles of his papers attest this. We find, 'The 
 Mechanical Production of Magnetism ' ; ' The Mechanical 
 Production of Electricity'; 'The Mechanical Causes of 
 Precipitation'; 'The Mechanical Origin of Corrosiveness 
 and Corrosibility ' ; and even, ' The Mechanical Produc- 
 tion of Tastes and Colours.' The series finishes with ' The 
 Mechanical Origin of Heat and Cold.' To produce heat 
 it is necessary ' that the moving particles should be small'; 
 and ' agitation is requisite to heat ' ; in fact, a statement, 
 in language of the time, of modern views. In accounting 
 for the decomposition of bodies by heat, his words are : 
 ' It rather seems that the true and genuine property of 
 heat is to set amoving arid thereby dissociate the particles 
 of matter.' 
 
 In spite of Boyle's numerous attempts to account for 
 natural phenomena in terms of matter and motion, his 
 modesty led him to make this statement : ' Having met 
 with many things of which I could give myself no probable 
 cause, and some things to which several causes may be 
 assigned, so differing as not to be able to agree in anything 
 unless in their all being probable enough;.! have often 
 
THE GREAT LONDON CHEMISTS 29 
 
 found such difficulty in searching into the cause and 
 manner of things, and I am so sensible of my own disability 
 to surmount these difficulties, that I dare speak posi- 
 tively of very few things except of matters of fact.' This, 
 I think, is in the main still our position. 
 
 Boyle's claim to rank as a 'Great London Chemist' 
 rests upon his having taken up his residence here from 
 the year 1668, until his death, which took place on the 
 last day of the year 1691, in the sixty-fifth year of his 
 age. But he was not a Londoner by birth. He was an 
 Irishman, born at Lismore in County Waterford, and of 
 noble parentage, for he was the seventh son, and the 
 fourteenth child, of the Earl of Cork. He was educated as 
 a child at home ; but at the age of eight he was sent to 
 Eton, where, as he says, ' he lost much of that Latin he 
 had got ; for he was so addicted to the more solid parts of 
 knowledge, that he hated the study of bare words natur- 
 ally.' At the age of eleven (they were precocious in those 
 days) his career at Eton was over ; and he was sent with 
 a French tutor, along with his brother, to Geneva, where 
 he pursued his studies for twenty-one months, and then 
 went to Italy. There he stayed until 1642; when his 
 father's finances having become embarrassed, owing to the 
 breaking out of the great Irish rebellion, Boyle returned 
 home, to find his father dead. Two estates had been left 
 to him ; one at Stalbridge, in Dorsetshire, where he pro- 
 ceeded to reside. In 1654, when twenty-seven years of 
 age, he removed to Oxford, in order to associate himself 
 with a number of men who had united themselves into a 
 society, under the name of the 'Philosophical College/ 
 This society afterwards moved its headquarters to London ; 
 and in 1663 it was incorporated by Charles n., under the 
 name of the ' Royal Society of London/ its object being 
 the ' Promotion of Natural Knowledge.' 
 
 Boyle's name is frequently mentioned in the first few 
 
30 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 volumes of ' The Transactions.' Thus we find on January 2, 
 1601, that 'Mr. Boyle was requested to bring in his 
 cylinder, and to show at his best convenience the experi- 
 ment of the air ' ; but his convenience was long in arriv- 
 ing, for on March the 20th ' Mr. Boyle was requested to 
 remember his experiment of the air,' and on April 1 ' he 
 was desired to hasten his intended alteration of his air- 
 pump.' On May 15, 'Mr. Boyle presented the Society 
 with his engine,' and with it numerous experiments 
 were made in the presence of members of the Society. 
 In such ' philosophical ' pursuits he spent his uneventful 
 life; and, to quote his own words, from a biographical 
 sketch drawn up by himself at an advanced period of his 
 life, he says : ' To be such parents' son, and not their 
 eldest, was a happiness that our Philarethes [a lover of 
 virtue himself] would mention with great expressions of 
 gratitude ; his birth so suiting his inclinations and designs, 
 that had he been permitted an election, his choice would 
 scarce have altered God's discernment.' 
 
 Cavendish, like Boyle, was also of noble birth. He was 
 the son of Lord Charles Cavendish, himself the third son 
 of the second Duke of Devonshire. His mother was Lady 
 Anne Grey, fourth daughter of Henry, Duke of Kent. 
 But except in the fact of their both being of the higher 
 rank of society, and in their both being addicted to the 
 pursuit of science, they have little in common. Boyle's 
 mind roamed over the whole domain of nature ; his writ- 
 ings treat of religious, philosophical, and scientific subjects 
 with a fulness and lack of mental reserve which testify 
 to his frank, transparent character. His motto was Nihil 
 humanum a me alienum puto ; and he carried this motto 
 into his life and work. Cavendish, on the other hand, 
 was by nature very shy and reserved ; he had no friends, 
 and few acquaintances; and instead of discussing the 
 whole of nature, as did Boyle, he limited himself to the 
 
THE GREAT LONDON CHEMISTS 31 
 
 investigation of a few problems of first-rate importance. 
 His work is characterised by the utmost accuracy and 
 elegance ; and he was cautious to an extreme in announc- 
 ing his conclusions. Both types of mind have their good 
 side ; but in their case one might have wished for a little 
 more moderation. Had Boyle not been so many-sided, he 
 might have advanced science more by accurate experi- 
 mental work ; and had Cavendish not been so reserved, 
 he would have done more good to his contemporaries, and 
 he would certainly have been a happier man. Neither 
 was married; and it is perhaps legitimate to draw the 
 conclusion that man's nature does not culminate in its 
 best without the influence of a helpmeet. 
 
 Like Boyle's, Henry Cavendish's life was an uneventful 
 one, and may be told in a few words. He was born on the 
 10th October 1731, at Nice, where his mother had gone 
 for her health. She died when he was two years old. In 
 1742, he became a pupil of Dr. Newcome, at Hackney 
 School, where he stayed until 1749 ; in that year, he 
 matriculated at Cambridge, and entered as a student at 
 Peterhouse. In 1753, he left without taking his degree; 
 he probably went to London ; but all details of his life are 
 lacking for the next ten years, though it is probable that 
 he spent the major part of his time in mathematical and 
 physical studies, and in research in the stables belonging 
 to his father's town house, which he had fitted up as a 
 laboratory. It was not until 1766 that he summoned up 
 resolution enough to publish; although his note-books 
 show that in 1764 he had begun to make experiments 
 which would have been well worth recording. From that 
 time forward, until 1809, the year before his death, his 
 papers appeared in constant succession. There was little 
 interruption to this incessant work, unless we consider a 
 series of journeys made through various parts of England 
 and Wales with the object of studying the geology of the 
 
32 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 country, and the manufactures carried on in the various 
 industrial centres, as a species of holiday. There was 
 no weekly interruptions to his labours; Sunday as well 
 as weekday was devoted to research, and so the years 
 glided past. During his father's lifetime, he is said to 
 have had an income of 500 a year ; but at his father's 
 death in 1783, and afterwards, owing to the legacy of an 
 aunt, he became possessed of enormous riches. Indeed, 
 M. Biot, in pronouncing a biographical oration on Caven- 
 dish, used the phrase : ' II etait le plus riche de tons les 
 savants, et probablement aussi, le plus savant de tous les 
 riches? 
 
 His town house was at the corner of Montague Place 
 and Gower Street ; visitors, however, were rarely ad- 
 mitted ; and Cavendish kept his library for his own use 
 and for that of the scientific public in a separate house in 
 Dean Street, Soho. To this library he went for his own 
 books, signing a formal receipt, as one would do at a 
 public library, for each one borrowed. 
 
 His laboratory was a villa at Clapham. The upper 
 rooms were an astronomical observatory. Here he 
 occasionally entertained friends, but in an unostentatious 
 way. His standing dish was a leg of mutton. It is 
 related that on one occasion, when the unprecedented 
 number of five guests had been invited, his housekeeper 
 ventured to point out that one leg of mutton would be 
 insufficient fare for so many ; his answer was, ' Well, then, 
 get two.' Several of his contemporaries have left a 
 record of their personal impressions of him. Professor 
 Playfair described him as of an awkward appearance, 
 without the look of a man of rank. He spoke very 
 seldom, and then with great difficulty and hesitation, but 
 exceedingly to the purpose, his remarks either displaying 
 some excellent information, or drawing some important 
 conclusion. An Austrian gentleman to whom he had 
 
THE GREAT LONDON CHEMISTS 33 
 
 been introduced, after the fashion of his country, assured 
 him that his principal reason for coming to London was 
 to see and converse with one of the greatest ornaments of 
 his age, and one of the most illustrious philosophers that 
 ever existed. To all these high-flown speeches Mr. Caven- 
 dish answered not a word, but stood with his eyes cast 
 down, quite abashed and confounded. At last, spying an 
 opening in the crowd, he darted through it with all the 
 speed he could muster, nor did he stop until he reached 
 his carriage, which drove him directly home. Sir Hum- 
 phry Davy said of him : ' His voice was squeaking, his 
 manner nervous ; he was afraid of strangers, and seemed, 
 when embarrassed, even to articulate with difficulty. He 
 wore the costume of our grandfathers; was enormously 
 rich, but made no use of his wealth.' And Lord 
 Brougham's recollection was that he would often leave 
 the place where he was addressed, and leave it abruptly, 
 with a kind of cry or ejaculation, as if scared and dis- 
 turbed. ' I recollect/ said Lord Brougham, ' the shrill cry 
 he uttered, as he shuffled quickly from room to room, 
 seeming to be annoyed if looked at, but sometimes 
 approaching to hear what was passing among others/ 
 
 On occasion, he was not ungenerous, although the 
 thought of giving did not occur to him. When dining 
 one evening at the Royal Society Club, some one present 
 mentioned the name of a gentleman who had previously 
 acted as a temporary librarian in his library. Mr. Caven- 
 dish said, ' Ah ! poor fellow, how does he do ? How does 
 he get on ? ' 'I fear very indifferently/ said this person. 
 ' I am sorry for it/ said Mr. Cavendish. ' We had hopes 
 that you would have done something for him, sir/ ' Me, 
 me, me, what could I do ? ' 'A little annuity for his life ; 
 he is not in the best of health.' 'Well, well, well, a 
 cheque for 10,000, would that do ? ' '0 sir, more 
 than sufficient, more than sufficient/ 
 
34 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Solitary he lived, and solitary was his death. Having 
 been ill for several days, his valet was called to his bed- 
 side, and told to summon Lord George Cavendish, as soon 
 as he should be dead. In about half an hour he again 
 summoned the servant, and made him repeat the 
 message. He then said, ' Right. Give me the lavender 
 water. Go.' Half an hour later the servant returned to 
 his room, and found that he had expired. 
 
 If Boyle found interest in all things human, Cavendish 
 appeared to take no thought of anything, except 
 phenomena. As his biographer, Dr. George Wilson, said, 
 his motto was Panta metro, kai arithmo, kai stathmo 
 (Tlavra /jLerpy, Kai apiO/jbw, Kai araOfjiq)). This we shall 
 now learn, from a short consideration of his work. 
 
 Cavendish's earlier work is only to be found in his un- 
 published papers. It appeared to have been his habit, 
 for some time, to write an account of his experiments, 
 without any intention of bringing them to the notice of 
 the public. An account of two long investigations was 
 found among his papers, after his death, of a date con- 
 siderably prior to that on which his first memoir 
 appeared in the Philosophical Transactions. The first 
 of these deals with the differences between 'regulus of 
 arsenic' (metallic arsenic) and its two oxides. He con- 
 cluded that arsenic oxide was ' more thoroughly deprived 
 of its phlogiston ' (in modern language, more thoroughly 
 oxidised) than arsenious oxide; and the latter, than 
 arsenic itself. The paper also contains speculations on 
 the nature of the red fumes obtained in the conversion 
 of arsenious to arsenic oxide by means of nitric acid ; 
 speculations which were afterwards to bear rich fruit, in 
 his work on the composition of air. 
 
 Another of his unpublished researches deals with heat. 
 Cavendish discovered independently the laws of specific 
 heat ; and he collected tables of the specific heats of many 
 
THE GREAT LONDON CHEMISTS 35 
 
 substances. He also was acquainted with what Black 
 termed ' latent heat/ that is, the heat absorbed during the 
 evaporation of liquids, or which is evolved during the 
 condensation of gases or vapours, or the solidification of 
 liquids. 
 
 As this essay deals with Cavendish as a chemist, I shall 
 treat very shortly of his physical work. One of the most 
 important of his investigations has reference to the 
 cause of the shock given by that curious fish the 
 torpedo. By constructing a species of artificial torpedo, 
 he proved that the shock was due to an electric discharge ; 
 and what is more, he was the first to distinguish between 
 electric quantity and electric intensity. Indeed, these 
 terms are due to him, as Faraday has acknowledged. 
 
 In 1783, 1786, and 1788, he published three papers on 
 freezing, in which his views on the nature of heat were 
 expounded. The first of these deals with the freezing of 
 mercury ; the second and third, with the congelation of 
 the mineral acids, and of alcohol. He objected to Black's 
 expression, ' the evolution, or setting free of latent heat/ 
 as involving an hypothesis that the heat of bodies is 
 owing to their containing more or less of a substance 
 called the matter of heat. He preferred to adopt Boyle's 
 and Sir Isaac Newton's supposition that heat consists in 
 the internal motion of the particles of bodies. And he 
 therefore uses the expression ' heat is generated.' 
 
 An interesting part of the last of these papers is a 
 passage in which he anticipates Richter's tables of the 
 equivalents of the acids and bases, not by any elaborate 
 disquisition, but as a device for estimating the strength of 
 sulphuric acid. In 1788 he wrote : ' The method I used 
 was to find the weight of the plumbum vitriolatum formed 
 by the addition of sugar of lead, and from thence to com- 
 pute the strength, on the supposition that a quantity of 
 oil of vitriol, sufficient to produce 100 parts of plumbum 
 
36 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 vitriolatum, will dissolve 33 of marble; as I found by 
 experiment that so much oil of vitriol would saturate as 
 much fixed alkali as a quantity of nitrous acid sufficient 
 to dissolve 33 of marble.' Richter's tables were published 
 in 1792. Cavendish's remarks involve a knowledge of 
 fixity of proportion, and also of reciprocal proportions; 
 doctrines which were after nearly twenty years pro- 
 pounded by Dalton. 
 
 Perhaps the most important piece of physical work 
 ever performed was Cavendish's determination of the 
 constant of gravitation, or as it is often called, ' the weight 
 of the earth.' The experiment is usually spoken of as 
 the 'Cavendish experiment,' although the method of 
 executing it was first suggested by the Rev. John Mitchell. 
 A delicate torsion balance, suspended by a wire, had 
 leaden balls suspended at each end. Two heavy spherical 
 masses of metal were brought near the balls, so that their 
 attraction tended to draw the two balls aside. The de- 
 viation of the arms was observed, or calculated from the 
 time of vibration ; and from the data found, it is easy to 
 calculate the attraction of a sphere of water, equal in 
 mass to the ball or a similar ball resting on its surface ; 
 and so to determine the density of the earth, knowing the 
 attraction which it exerts on the ball. The results 
 obtained compared very favourably with the best results 
 obtained by other observers, using the utmost precau- 
 tions ; and it is a very remarkable instance of Cavendish's 
 experimental skill and ingenuity. 
 
 We have here to consider more particularly Caven- 
 dish's chemical work. It was of the highest order, and 
 bears the imprint of a master mind, guiding a master 
 hand. 
 
 Before Black's time, the word * gas ' had no plural. 
 Indeed, what we now know as a gas was set down as a 
 modification of ordinary air. Black, however, proved that 
 
THE GREAT LONDON CHEMISTS 37 
 
 a gas could be contained in a solid state, as for instance 
 in carbonate of linie or of magnesia, or in what were then 
 known as the ' mild alkalies ' ; and that it could possess 
 weight. He termed carbonic anhydride 'fixed air.' 
 Cavendish's first published paper deals with 'Factitious 
 Air'; it appeared in 1766, seven years after the publica- 
 tion of Black's memoir on ' Magnesia alba, Quick-lime, and 
 other Alkaline Substances.' ' Factitious air ' was defined 
 by Cavendish as ' any kind of air which is contained in 
 other bodies in an unelastic state, and is produced from 
 thence by art.' He first treats of hydrogen, next of 
 carbon dioxide, and lastly of gases evolved during fermen- 
 tation and putrefaction. Although not the first to prepare 
 hydrogen (for it must have been known for centuries that 
 an inflammable gas was evolved on bringing metals into 
 contact with certain dilute acids), yet he was the first to 
 characterise hydrogen as a definite substance, and not a 
 mere variety of common air. He prepared this gas from 
 zinc, iron, or tin, and weak sulphuric or hydrochloric acid. 
 He found that the substance was identical in each case, 
 by weighing a known volume ; which he did with no great 
 accuracy in a bladder, but with considerable exactitude 
 by weighing a flask containing, for example, zinc and 
 acid, unmixed ; and after mixture, weighing again ; a 
 further experiment served to determine the volume of gas 
 obtainable from a known weight of zinc. Another method 
 of establishing their identity, curious to our notions, was 
 to mix the sample with a known volume of air, and 
 estimate the loudness of the explosion which took place 
 on applying a flame. Cavendish also prepared ' the 
 volatile sulphurous acid,' by substituting concentrated 
 sulphuric acid for dilute; and a non-inflammable air 
 (nitric oxide), by the action of nitric acid. 
 
 Cavendish did not suppose that the 'air' came from 
 the acid, but from the metal. It must be remembered 
 
38 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 that at that time, the current doctrine was that when 
 substances burn, they lost a principle, to which the name 
 ' phlogiston ' had been applied by Stahl, the propounder of 
 the doctrine. The hydrogen evolved was at first sup- 
 posed by Cavendish to be the long-sought phlogiston 
 itself. But fuller consideration induced him to change 
 his view ; and he subsequently held that hydrogen was a 
 hydrate of phlogiston, or a compound of that hypothetical 
 substance with water. In this paper, too, as well as in 
 one which followed, Cavendish added many facts to those 
 which had been published by Black on the properties of 
 carbonic acid; but as these contain little of theoretical 
 interest, they need not detain us. 
 
 Seventeen years later, the next of his ' pneumatic ' 
 papers was published. It was entitled, ' An Account of a 
 New Eudiometer.' The eudiometer, which in no way 
 resembled the picture of the instrument usually ascribed 
 to him, was designed, not for the explosion of a mixture 
 of two gases, but for the removal of oxygen from air, by 
 means of nitric oxide. With its aid, he determined the 
 composition of many samples of air, and his final result, 
 translated into our method of statement, gave for the 
 proportion of oxygen in air the extraordinarily accurate 
 number, 20*83 per cent. 
 
 Cavendish's next paper in order of publication (1784) 
 gave the results of experiments begun in 1781. Its title 
 is ' Experiments on Air.' The object of these experiments 
 was to 'find out the cause of the diminution which com- 
 mon air is well known to suffer by all the various ways 
 in which it is phlogisticated, and to discover what becomes 
 of the air thus lost or condensed.' His first idea was that 
 this treatment might result in the formation of ' fixed 
 air.' But having disproved this, he proceeded to try 
 whether, as some of Priestley's experiments appeared to 
 show, ' the dephlogisticated part of common air might 
 
THE GREAT LONDON CHEMISTS 39 
 
 nob by phlogistication be changed into nitrous or vitri- 
 olic acid ' ; i.e. whether oxygen, by reduction, might not 
 be converted into nitric or sulphuric acid. Absorbing 
 the oxygen by burning sulphur, he failed to find nitric 
 acid; and using nitric oxide as the absorbent, the re- 
 sulting nitrate and nitrite contained no sulphate. He 
 therefore tried firing a mixture of hydrogen and air by 
 means of an electric spark ; an experiment which led to 
 the discovery of the composition of water. Having 
 burned 500,000 grain measures of inflammable air (hydro- 
 gen) with two and a half times its volume of common 
 air, he collected upwards of 135 grains of water, ' which 
 had no taste nor smell, and which left no sensible sedi- 
 ment when evaporated to dryness.' 
 
 It is impossible in a short sketch like the present to 
 enter into a description of the exceedingly ingenious 
 experiments devised to show whence the acid was derived 
 which is formed when the hydrogen is present in insuf- 
 ficient amount ; we must be content to remember that in 
 default of hydrogen with which to combine, some of the 
 oxygen unites with the nitrogen, yielding nitrous and 
 nitric acids. 
 
 Although Cavendish employs the language of the 
 phlogistic theory in stating his conclusions, yet it must 
 not be supposed that he was ignorant of the newer views, 
 propounded by Lavoisier. In the memoir which we have 
 been considering, he states his conclusions in the new 
 phraseology ; but he concludes as follows : ' It seems, 
 therefore, from what has been said, as if the phenomena 
 of nature might be explained very well on this principle 
 without the help of phlogiston; and indeed, as adding 
 dephlogisticated air to a body comes to the same thing 
 as depriving it of its phlogiston, and adding water to it, 
 and as there are perhaps no bodies entirely destitute of 
 water, and as I know no way by which phlogiston can be 
 
40 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 transferred from one body to another without leaving it 
 uncertain whether water is not at the same time trans- 
 ferred, it will be very difficult to determine by experiment 
 which of these opinions is the truest; but as the com- 
 monly received principle of phlogiston explains all 
 phenomena, at least as well as Mr. Lavoisier's, I have 
 adhered to that.' We shall meet with this same difficulty 
 again, when we consider Davy's experiments, which led 
 to true views concerning the nature of chlorine. 
 
 Cavendish's aim in these experiments, stated in modern 
 language, was to find out what becomes of the oxygen, 
 when substances burn in air ; whether the production of 
 carbon dioxide is a constant accompaniment of com- 
 bustion. He mentions five ways in which air may be 
 deprived of oxygen, namely, by the calcination of rnetals ; 
 by burning in it sulphur or phosphorus; by mixing it 
 with nitric oxide; by exploding it with hydrogen; and 
 lastly by submitting it to the action of electric sparks. 
 In the second series of his experiments on air, he ex- 
 amines in detail the action of a continued rain of sparks 
 on air ; and this led to the discovery of the composition 
 of nitric acid ; for the ' caustic lees ' on evaporation to 
 dryness ' left a small quantity of salt, which was evidently 
 nitre, as appeared by the manner in which paper im- 
 pregnated with a solution of it burned.' But he doubted 
 whether ' there are not, in reality, many different sub- 
 stances confounded by us under the name of phlogisticated 
 air.' He ' therefore made an experiment to determine 
 whether the whole of a given portion of the phlogisticated 
 air of the atmosphere could be reduced to nitrous acid, 
 or whether there was not a part of a different nature 
 from the rest, which would refuse to undergo that change.' 
 On experiment, he found that ' if there is any part of the 
 phlogisticated air of our atmosphere which differs from 
 the rest, and cannot be reduced to nitrous acid, we may 
 
THE GREAT LONDON CHEMISTS 41 
 
 safely conclude that it is not more than T ^ part of the 
 whole.' Here he was nearly right; about one per cent, 
 is actually left ; and it has been recently recognised as a 
 separate element, and named Argon. And still more 
 recently, the argon has been shown to contain a small 
 proportion of other gases, also elements, to which the names 
 helium, neon, krypton and xenon have been given. This 
 paper was the last on chemical subjects published by 
 Cavendish. 
 
 These two men, Boyle and Cavendish, both rank as 
 great men. The first has been termed with justice f the 
 father of modern chemistry ' ; the second by ' weighing the 
 earth/ and by establishing the composition of water and 
 of air, has even more decided claims to that title. Each 
 was in advance of his age : Boyle by reason of his calm 
 philosophical spirit, and clear judgment; Cavendish in 
 the power he possessed, in an age of qualitative en- 
 deavours, of carrying out quantitative experiments with 
 the most refined accuracy, and of drawing from them 
 correct conclusions. 
 
 II. DAVY AND GRAHAM 
 
 Between a prospect over an extensive landscape, and a 
 retrospect in history, an instructive analogy may be 
 drawn. It is true that when the spectator is removed 
 from the object by a great distance, whether of time or 
 space, its appearance is ill-defined and hazy, as are to us 
 the personalities of the ancient Egyptians, Greeks, and 
 Arabians ; and just as the imagination supplies details to 
 the distant features of a landscape, details which may or 
 may not be in consonance with fact, so through the mists 
 of time we are apt to read into the writings of the 
 
42 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 ancients ideas which have their origin rather in our 
 own brains than in their works. Objects in the middle 
 distance are perhaps most truthfully interpreted. They 
 are not obscured by the haze of perspective nor by the 
 multitudinous aggregations of propinquity. So it is with 
 Boyle and with Cavendish. But with Davy, and with 
 Graham, whose lives and works are to form the subject 
 of this essay, it is difficult to select from their writings 
 those salient features which will, in the course of another 
 half-century, stand out clearly and luminously among 
 the labours of their contemporaries. In chemical and 
 physical work, as in life, safety lies in a happy mean ; and 
 it shall be my endeavour to avoid unimportant details, 
 while presenting the main characteristics of the work of 
 these two remarkable men. The difficulty is to know 
 what to omit ; for that which appears unimportant to-day 
 may to-morrow turn out to be essential to the fundamental 
 doctrines of our science. 
 
 At the time when Cavendish was beginning his splendid 
 series of experiments on gases, Humphry Davy, an infant 
 of two, was beginning to show signs of that ability which 
 so remarkably distinguished him in after life. At that 
 age, he could speak fluently ; a year or two later, he was 
 sent to school, where he learned to read and write before 
 he was six ; and in his seventh year he was sent to the 
 Grammar School at Truro, his native place. Looking 
 back on his experiences there, from the standpoint of a 
 young man of twenty-two, he wrote : ' I consider it fortu- 
 nate that I was left much to myself when a child, and 
 put upon no particular plan of study, and that I enjoyed 
 much idleness at Mr. Coryton's school.' Do not we err 
 in insisting too much on the systematic employment of 
 time by the boys of our modern schools ? For, be it re- 
 membered, the compulsory cricket and football, so com- 
 mon in our schools, is to some boys the hardest task 
 
THE GREAT LONDON CHEMISTS 43 
 
 they have to master, and leaves no time for salutary 
 idleness. 
 
 Like many boys, Davy entered the study of chemistry 
 through the doorway of fireworks. His favourite amuse- 
 ments were fishing, and the art of rhyming. During his 
 whole life, he never lost the taste for these two pursuits ; 
 and though it must be confessed that he was a more 
 successful fisher than poet, still his verses have a certain 
 amount of merit, and betoken a considerable gift of 
 imagination, necessary to the higher achievements in 
 science, as he indicates in the two stanzas which I venture 
 to quote : 
 
 While superstition rules the vulgar soul, 
 
 Forbids the energies of man to rise, 
 Raised far above her low, her mean control, 
 
 Aspiring genius seeks her native skies. 
 
 She loves the silent, solitary hours ; 
 
 She loves the stillness of the starry night, 
 When o'er the bright'ning view Selene pours 
 
 The soft effulgence of her pensive light. 
 
 In his later efforts he preferred decasyllabics; and 
 though his sentiments thus expressed are praiseworthy, 
 his execution rarely exceeds the level demanded from a 
 poet laureate. 
 
 At the early age of fifteen, his school education was at 
 an end. For the next year he continued in the ' enjoy- 
 ment of much idleness.' But in the beginning of the 
 year 1795 he was apprenticed to Mr. Borlase, surgeon and 
 apothecary, in his native town. Then the demon of work 
 seized on him, and he threw himself into the task of self- 
 improvement with irresistible ardour. His scheme of 
 study is so remarkable, and so extensive, that I cannot 
 
44 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 resist the temptation to quote it at full length. Here 
 it is : 
 
 1 . THEOLOGY OR EELIGION, taught by Nature. 
 
 ETHICS, or moral virtues, by Revelation. 
 
 2. GEOGRAPHY. 
 
 3. MY PROFESSION 4. LANGUAGE 
 
 1. Botany. 1. English. 
 
 2. Pharmacy. 2. French. 
 
 3. Nosology. 3. Latin. 
 
 4. Anatomy. 4. Greek. 
 
 5. Surgery. 5. Italian. 
 
 6. Chemistry. 6. Spanish. 
 
 5. LOGIC. 7 - Hebrew. 
 
 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. 8. HISTORY AND CHRONOLOGY. 
 9. RHETORIC AND ORATORY. 10. MATHEMATICS. 
 
 Which of us has undertaken a course of study so exten- 
 sive, and so inclusive ? 
 
 Following out this course, not quite in the prescribed 
 order, however, he reached the subject of chemistry in 
 January 1798. His textbooks were Lavoisier's Chemistry 
 and Nicholson's Dictionary of Chemistry. He kept up 
 the study of mathematics during the whole course, having 
 begun in 1796 : for he remarks on its usefulness as a 
 preliminary to the study of chemistry and physics. In 
 his self-imposed task of mastering chemistry, he at once 
 began practical work, having fitted up a small laboratory, 
 furnished with the very simplest and most inexpensive 
 
THE GREAT LONDON CHEMISTS 45 
 
 apparatus, in Mr. Tonkins's house. About four months 
 after beginning his chemical studies he was in corre- 
 spondence with Dr. Beddoes, a medical man residing at 
 Clifton, on the subject of heat and light. This corre- 
 spondence was fraught with momentous consequences for 
 Davy; for it led to his being offered the position of 
 superintendent of the 'Pneumatic Institution,' founded 
 by the doctor, with the help of Josiah Wedgwood and Mr. 
 Gregory Watt, youngest son of James Watt, with the 
 object of experimenting with the gases, at that time 
 recently discovered, in order to ascertain whether they 
 would prove suitable as remedial agents. 
 
 In reviewing the career of a man, it is interesting to 
 note the motives which underlie his actions. The latter, 
 indeed, may not always be worthy of the sentiments which 
 give them birth, but it is just to give credit for pure 
 intentions, and to form an estimate of character by taking 
 both motive and action into consideration. In one of the 
 earliest of Davy's notebooks, intended for no eye but his 
 own, there is this entry : ' I have neither riches, nor 
 power, 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.' 
 And again, in 1821, nearly twenty-five years later, his 
 diary contains the aspiration, ' May every year make me 
 better more useful, less selfish, and more devoted to the 
 cause of humanity and science.' These are noble words, 
 and they lead one to form a high estimate of the charac- 
 ter of Humphry Davy. 
 
 In January 1799 he went to the Pneumatic Institute, 
 and worked under the patronage of Dr. Beddoes. By the 
 following year he had finished his classical research on 
 nitrous oxide, and had discovered and investigated its 
 remarkable anaesthetic properties. He also discovered 
 the composition of nitric acid, nitric oxide, nitric peroxide, 
 
46 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 and ammonia. By 1801 he had begun his experiments 
 with the ' galvanic battery,' which was to be so fruitful of 
 important results in his hands. During these two years, 
 he published no fewer than nine papers in the scientific 
 journal of his time, Nicholsons Journal, the predecessor 
 of the Philosophical Magazine, the result of astonishing 
 industry. 
 
 At this period of his life, Davy's acumen led him to 
 avoid undue theorising, and to endeavour to accumulate 
 facts. His own words are : ' When I consider the variety 
 of theories that may be formed on the slender foundation 
 of one or two facts, I am convinced that it is the business 
 of the true philosopher to avoid them altogether. It is ' 
 more laborious to accumulate facts than to reason con- 
 cerning them ; but one good experiment is of more value 
 than the ingenuity of a brain like Newton's.' In the light 
 of this opinion, it is interesting to examine the programme 
 which he laid down for himself at the time. It was 
 written in the spring of 1799, and is as follows : 
 
 * To decompose the muriatic, boracic, and fluoric acids ; 
 to try triple affinities, and the contact with heated com- 
 bustible bodies at a high temperature. 
 
 ' To ascertain all the phenomena of oxydation. 
 
 ' To discover with accuracy the vegetable process.' 
 
 The decomposition of the muriatic and the boracic 
 acids was successfully accomplished at a much later date. 
 But the ' phenomena of oxydation ' are even now known 
 only imperfectly. He contributed useful facts, however, 
 as we shall see, to our knowledge of ' the vegetable 
 process.' 
 
 Consistently with these ideas regarding the relative 
 merits of theory and practice, Davy made his greatest 
 successes in the realm of facts. Where he attempts 
 theorising, the results are not happy. It is true that he 
 did not risk the publication of his theories ; but those 
 
THE GREAT LONDON CHEMISTS 47 
 
 revealed by his notebooks have not much to recommend 
 them. He allowed his imagination, of which he possessed 
 a rich share, full scope in other directions. Many of his 
 imaginative projects were, however, not realised. Among 
 them may be mentioned an epic poem, in six books, 
 entitled The Epic of Moses, written, what there is of it, in 
 decasyllabics. He possessed a deeply religious nature; 
 and he regarded ' this little earth as but the point from 
 which we start towards a perfection bounded only by 
 infinity.' 
 
 In 1801 Davy was recommended by Professor Hope of 
 Edinburgh for the lectureship at the Royal Institution, 
 which had been founded a few years previously by Count 
 Rurnford, on the resignation of Dr. Garnet, the first 
 Professor of Chemistry there. He delivered his first 
 lecture in April 1801, and he at once achieved a great 
 success. To quote from an account by a contemporary 
 witness : ' The sensation created by his first course of 
 lectures at the institution, and the enthusiastic admira- 
 tion which they obtained, is at this period hardly to be 
 imagined. Men of the first rank and talent the literary 
 and the scientific, the practical and the theoretical blue- 
 stockings and women of fashion, the old and the young, all 
 crowded, eagerly crowded, the lecture-room. His youth, his 
 simplicity, his natural eloquence, his chemical knowledge, 
 his happy illustrations and well-conducted experiments, ex- 
 cited universal attention and unbounded applause. Com- 
 pliments, invitations, and presents were showered on him in 
 abundance from all quarters ; his society was courted by 
 all, and all appeared proud of his acquaintance.' With 
 all these temptations to neglect his work, he remained 
 faithful to his charge. In 1803 he wrote : ' My real, my 
 waking existence is among the objects of scientific 
 research. Common amusements and enjoyments are 
 necessary to me only as dreams to interrupt the flow of 
 
48 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 thoughts too nearly analogous to enlighten and vivify.' 
 Still many of our scientific workers of to-day would be 
 glad if they could extract as much leisure time from 
 amidst their daily employments. Davy generally entered 
 the laboratory about ten or eleven o'clock, and if uninter- 
 rupted, remained there till about three or four. His 
 evenings were almost invariably spent in dining out, and at 
 evening parties afterwards. ' To the frequenters of these 
 parties he must have appeared a votary of fashion, rather 
 than of science,' as his brother remarked. 
 
 Yet, during the years which followed, he accomplished 
 an immense amount of very remarkable work. Besides 
 investigating, by the request of the managers of the Royal 
 Institution, the chemistry of tanning, an investigation 
 which led to the use of catechu as a substitute for the 
 old-fashioned oak-bark, he lectured, by the request of the 
 Board of Agriculture, on ' The Connection of Chemistry 
 with Vegetable Physiology.' These lectures were given 
 every year, and in them were incorporated the results of a 
 considerable number of experiments made by him, or 
 under his direction, on the chemistry of plants. In 1813, 
 when he ceased to lecture on the subject, he published his 
 lectures, under the title The Elements of Agricultural 
 Chemistry. For the copyright of this work he received 
 one thousand guineas, and fifty guineas for each subse- 
 quent edition. Truly he was a fortunate man ! 
 
 Between January 1801 and April 1812 he accomplished 
 two of his most remarkable pieces of work ; first, on the 
 decomposition of the alkalies ; and second, on the nature 
 of chlorine. As his name rives chiefly in connection with 
 these two investigations, and in his research on the 
 nature of flame, which culminated in the invention of the 
 safety-lamp, I shall give some account of them in 
 minuter detail. 
 
 The Swedish chemist, Scheele, had discovered in 1774, 
 
THE GREAT LONDON CHEMISTS 49 
 
 that on treating manganese dioxide with hydrochloric 
 acid, or as it was then called ' spiritus salis/ in a flask to 
 which a bladder had been attached, a ' yellow air ' filled 
 the bladder, which possessed a suffocating smell, which 
 bleached litmus paper and flowers, and which attacked 
 metals, even gold. He named this new gas ' dephlogisti- 
 cated marine acid/ imagining that the manganese had 
 deprived the marine acid of its ' phlogiston,' and that it 
 had consequently been converted into the yellow gas. 
 Count Berthollet, in 1788, prepared this gas, and on 
 saturating with it water cooled with ice, he discovered 
 that a solid crystalline hydrate separated from the water. 
 Having exposed a solution, thus obtained, to sunlight, he 
 noticed the evolution of oxygen, and he, therefore, con- 
 cluded that the dephlogisticated marine acid was in 
 reality a compound of marine acid with oxygen, since, 
 under the action of sunlight, oxygen was evolved, and 
 marine acid left. This idea, according to Berthollet, 
 readily explained the action of the solution of the yellow 
 gas on metals; for it might be supposed to give up to 
 metals its oxygen, and the metallic oxide would then, as 
 usual, dissolve in the marine acid. In consequence of 
 this observation, M. de Morveau, in conjunction with 
 Lavoisier, Berthollet, and de Fourcroy, in drawing up 
 their Meihode de nomenclature chimique, proposed for 
 the gas the name 'Oxymuriatic acid.' To follow the 
 further history of chlorine, it will be advisable to pause, 
 and consider Davy's researches on the^alkali metals. 
 
 Before leaving Bristol, Davy had* begun experiments 
 with the galvanic battery. On reaching London, he con- 
 tinued his electrical work; and in 1807 he published a 
 remarkable paper on the 'Chemical Agencies of Elec- 
 tricity.' It had been shown that when the two poles of a 
 battery with platinum terminals were plunged into two 
 vessels of water, connected together by wet asbestos, or 
 
 D 
 
50 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 cotton wick, an acid appeared round the positive wire, and 
 an alkali round the negative wire. Davy showed by a 
 series of convincing experiments that the alkali is usually 
 potash or soda derived from the glass, and the acid 
 usually hydrochloric acid from the common salt present 
 as an impurity in the water. From experiments such as 
 these he evolved a theory that all substances which have 
 a chemical affinity for each other are in opposite states of 
 electrification, and that the positive pole attracts those 
 constituents of the solution which possess a negative 
 charge, while the negative pole attracts the positively 
 charged component. The more powerful the battery, 
 the greater the force of these attractions and repulsions. 
 For example, oxygen and acids are negative bodies, for 
 they are attracted by the positive pole, and liberated 
 there; whereas metals and their oxides, and hydrogen, 
 nitrogen, carbon, and selenium are positive, because they 
 separate at the negative pole. It ought, therefore, to be 
 possible, by help of a sufficiently strong electric current, 
 to decompose any compound whatsoever. Davy carried 
 his inference farther, and suggested that the reason of 
 chemical attraction is the oppositely charged state of the 
 components of a compound. A compound is an elec- 
 trically neutral body, for the constituents of the com- 
 pound, in uniting, have respectively equal and opposite 
 charges, which neutralise each other by the act of com- 
 bination. But a current of electricity, passing through 
 such a compound, might neutralise the electricity in each, 
 and so, by overcoming their attractions, decompose the 
 compound. 
 
 By applying these ideas, he succeeded in decomposing 
 the ' fixed alkalies,' as caustic soda and potash used to be 
 called, into oxygen, hydrogen, and the metals sodium and 
 potassium. Having failed to obtain any products from 
 aqueous solutions of these compounds, except oxygen and 
 
THE GREAT LONDON CHEMISTS 51 
 
 hydrogen, he next attempted to pass a very powerful 
 current through the fused alkalies. Potash was fused in 
 a platinum spoon, connected with the positive side of a 
 battery ; and a platinum wire, connected with the negative 
 pole of the battery, was dipped into the fused alkali. The 
 result was an intense light at the negative wire, and a 
 column of flame from the point of contact. On reversing 
 the current, 'aeriform globules, which inflamed in the 
 atmosphere, rose through the potash.' The substance 
 produced was evidently inflammable, and was destroyed 
 at the moment of liberation. Better results were obtained 
 by the use of slightly moist potash ; and small metallic 
 globules were collected, ' precisely similar in visible char- 
 acteristics to quicksilver.' c These globules numerous ex- 
 periments soon showed to be the substance I was in search 
 of, and a peculiar inflammable substance, the basis of 
 potash.' Soda gave an analogous result; and thus the 
 metals of the alkalies were discovered. 
 
 These new metals burned in oxygen, forming the 
 alkalies from which they had been obtained ; they also 
 burned in ' oxymuriatic acid/ forming ' muriates ' of potash 
 or soda. They decompose water with evolution of hydro- 
 gen, giving solutions of the respective alkalies ; and they 
 form compounds with sulphur and with phosphorus. 
 They reduce metals such as copper, iron, lead, and tin 
 from their oxides ; and they attack glass, apparently 
 liberating the ' basis of the silex.' 
 
 Fairly accurate estimations were made of the proportion 
 of these new metals in the alkalies, which were believed 
 by Davy to be oxides ; and thus the approximate composi- 
 tion of these compounds, which at one time were believed 
 to be elements, was definitely established. 
 
 Although similar phenomena were seen with the alka- 
 line earths 'barytes' and ' strontites,' it was not found 
 possible to isolate the metals ; but on electrolysing with a 
 
52 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 negative pole of mercury, amalgams were obtained, con- 
 taining the new metals barium and strontium ; while 
 from lime and magnesia, evidence was similarly obtained 
 that they consisted of metals, named by Davy calcium 
 and 'magnium.' On removing the mercury by distilla- 
 tion, white metallic residues were obtained, still containing 
 mercury, but oxidising rapidly in the air, to the respective 
 oxides. An account of these results was published in 
 1807 and 1808, in the Philosophical Transactions. 
 
 In December 1808, the celebrated paper on the elemen- 
 tary nature of chlorine was read. Having failed to obtain 
 any other products than hydrogen and oxygen on passing 
 a current through an aqueous solution of muriatic acid 
 gas in water (why, is not so apparent, unless only dilute 
 solutions had been employed), Davy treated dry muriatic 
 acid gas with potassium. The gas was absorbed, yielding 
 -% of its volume of hydrogen. He concluded from this 
 that dry muriatic acid gas contained at least one-third 
 of its weight of water, and that it had not been ' decom- 
 pounded ' by the potassium. His first attempt, therefore, 
 was directed to obtaining really dry muriatic gas. For 
 this object, he heated dry muriate of lime with dry sul- 
 phate of iron, with phosphoric glass, and with dry boracic 
 acid ; but without any evolution of gas, although when 
 water was added to the ignited mass, quantities of 
 muriatic gas were liberated. After numerous attempts of 
 the same kind, during which the chlorides of sulphur and 
 phosphorus were discovered, these substances were them- 
 selves submitted to the action of potassium, but without 
 the formation of any gaseous product. 
 
 In an appendix to these observations, which were pub- 
 lished as the Bakerian Lecture, Davy announces the view 
 that 'muriatic acid gas is a compound of a substance, 
 which as yet has never been procured in an uncombined 
 state, and from one-third to one-fourth of water, and that 
 
THE GREAT LONDON CHEMISTS 53 
 
 oxymuriatic acid is composed of the same substance (free 
 from water), united to oxygen.' His idea then was that 
 ' when bodies are oxidated in muriatic acid gas, it is by a 
 decomposition of the water contained in that substance, 
 and when they are oxidated in oxymuriatic acid, it is by 
 combination with the oxygen in that body.' Davy believed 
 that the chlorides all contained oxygen. 
 
 In a later paper, read in November 1809, he arrived at 
 the true explanation of these facts. It was based on 
 experiments on the ignition of charcoal to whiteness in 
 muriatic and oxymuriatic gases. No action occurred ; 
 and Davy began to doubt whether, as universally sup- 
 posed, these bodies contain any oxygen. He therefore 
 tried whether compounds produced by the action of oxy- 
 muriatic acid on tin, phosphorus, and sulphur would give 
 with ammonia precipitates of the oxides of these elements, 
 or any compounds containing oxygen; and his experi- 
 ments were attended with negative results. He next con- 
 sidered one argument that the so-called ' oxymuriatic acid ' 
 contained oxygen, viz. the fact that on treatment with 
 rnetals, hydrogen is evolved ; and in a further paper, read 
 in November 1810, he proved that on heating barium or 
 strontium in the gas, one volume of oxygen is liberated 
 for every two volumes of oxymuriatic acid absorbed. This 
 is exactly the amount of oxygen contained in the oxide ; 
 and experiments with other oxides of metals resulted in 
 similar liberation of all the oxygen previously combined 
 with the metal. From ttfese facts, Davy concluded that 
 ' to call a body which is not known to contain oxygen, and 
 which cannot contain muriatic acid, oxymuriatic acid, is 
 contrary to the principles of that nomenclature in which 
 it is adopted ' ; and he therefore proposed for the gas the 
 name chlorine. 
 
 Many derivatives of chlorine were made by Davy for 
 the first time ; among them were the oxygen compounds 
 
54 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 of chlorine. But he did not commit himself to the dog- 
 matic assertion that this gas is an element; on the con- 
 trary, he writes : ' In the views that I have ventured to 
 develop, neither oxygen, chlorine, nor fluorine are asserted 
 to be elements ; it is only asserted that, as yet, they have 
 not been decomposed.' It would be well, were all chemists 
 to imitate Davy's caution. 
 
 These views were combated by Gay-Lussac and The- 
 nard; but it would take too much time to follow the 
 contest. Suffice it to say, that Davy came off with flying 
 colours. 
 
 During all these years, honours were being showered on 
 Davy. In 1803, he was made a Fellow of the Royal 
 Society ; in 1807, he was chosen for its secretary, an office 
 which he held until 1812 ; and in the latter year he was 
 knighted. In his private diary, in which he transcribed 
 his inmost thoughts, there is a pleasant little sentence, 
 recording sentiments on the subject of honours: ' A man 
 should be proud of honours, not vain of them.' But 
 besides honours, wealth was also his portion ; for two 
 courses of lectures in Dublin, he was paid no less a sum 
 than 11 70! 
 
 In 1812, his Elements of Chemistry was published. It 
 was dedicated to his wife; for in that year he married 
 Mrs. Apreece. 
 
 In the same year, he nearly lost his sight by experi- 
 menting with chloride of nitrogen, which had recently 
 deprived its discoverer, Dulong, of a finger. In 1813, he 
 established the true nature of fluorine, and demonstrated 
 its analogy with chlorine; and towards the end of the 
 same year, he paid a visit to Paris, conveying with him a 
 portable laboratory, by help of which he proved the simi- 
 larity of iodine to chlorine. That element, which had 
 been discovered about two years previously by Courtois, 
 was supposed by Gay-Lussac to yield an acid identical 
 
THE GREAT LONDON CHEMISTS 55 
 
 with hydrochloric acid. Davy communicated his dis- 
 covery to Gay-Lussac, who by no means agreed with his 
 conclusions; and it was not until a considerable time 
 had elapsed, and the latter chemist had carried out his 
 masterly researches on iodine and its compounds, that he 
 became convinced of the correctness of Davy's views. 
 
 On his return from this Continental tour, he devoted 
 his time to the investigation of the nature of flame, with 
 the result that he discovered how to prevent flame from 
 spreading into the adjoining atmosphere, by surrounding 
 it with a sheath of wire-gauze ; the conducting power of 
 the gauze so cooling the explosive mixture of gases, that 
 they no longer inflame after traversing the gauze dia- 
 phragm. This invention was hailed with the greatest 
 satisfaction by the public, as well as by those whose 
 interest was bound up in mines; and in 1817, he was pre- 
 sented with a service of plate, valued at 2500, by the 
 owners of many important collieries. His services to 
 humanity were, indeed, valued so highly, that in the 
 following year a baronetcy was bestowed on him. And in 
 1820, on the death of Sir Joseph Banks, who had presided 
 over the meetings of the Royal Society for no less than 
 forty- one years, Sir Humphry Davy received the highest 
 honour which can be bestowed on a scientific man, in 
 being elected his successor. He resigned the presidency 
 in 1827. His own view regarding honours was : ' It is not 
 that honours are worth having, but it is painful not to 
 have them ' ; and again, ' It is better to deserve honours 
 and not to have them, than to have them and not deserve 
 them.' These sentiments remind one of Burns's rhyming 
 grace before meat : 
 
 Some hae meat, and canna eat, 
 
 And some wad eat that want it ; 
 But we hae meat, and we can eat, 
 
 And sae the Lord be thankit. 
 
56 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 During these years, Davy published many papers, having 
 relation to the preservation of metals by electro-chemical 
 means, with special reference to the preservation of the 
 copper sheathing of ships. In 1826, these, and other 
 similar inquiries, were summed up in the ' Bakerian ' 
 Lecture, on the Relation of Electrical and Chemical 
 Changes. 
 
 His scientific work, however, was nearly at an end ; for 
 in 1826 he had a slight shock of paralysis, and though he 
 lived until 1829, it was in a continual search for health. 
 He travelled much on the Continent, and made partial 
 recoveries ; but he was seized by a final stroke at Geneva 
 in May 1829, where he died, in his fifty-first year. 
 
 Sir Humphry Davy's work is well summed up in a 
 notice published in Silliman's American Journal of 
 Science and Arts: 'To conclude, we look upon Sir 
 Humphry Davy as having afforded a striking example of 
 what the Romans called a man of good fortune ; whose 
 success, even in their view, was not however the result of 
 accident, but of ingenuity and wisdom to devise plans, 
 and of skill and industry to bring them to a successful 
 issue. He was fortunate in his theories, fortunate in his 
 discoveries, and fortunate in living in an age sufficiently 
 enlightened to appreciate his merits/ But let him speak 
 his own epitaph; it is: 'My sole object has been to serve 
 the cause of humanity; and if I have succeeded, I am 
 amply rewarded in the gratifying reflection of having 
 done so.' 
 
 Fortunately for your patience, my task to-day is limited 
 to sketching the lives of those chemists who have gone 
 from among us. And confining myself to the names of 
 those who must pass without cavil as 'great/ that of 
 Graham presents itself. There have been men of con- 
 siderable ability, who have in their day done good and 
 
THE GREAT LONDON CHEMISTS 57 
 
 useful work ; such men as Turner, Graham's predecessor ; 
 Daniel, who gave us the battery known by his name; 
 Miller, to whose painstaking labours we owe the revision 
 of our standards of weight and measure ; and many others 
 of less eminence. But of these I can only mention the 
 names. 
 
 The city of Glasgow gave Graham to London ; Boyle 
 was an Irishman; Cavendish was born in France; and 
 Davy came from Cornwall. But London made some 
 return for depriving Glasgow of Graham ; for Penny was 
 a Londoner, who passed the major part of his life in 
 Glasgow, having been called thither as successor to 
 Graham. He, too, did good work in his day; he was 
 an extremely attractive lecturer, and may be said to have 
 brought the art of giving professional evidence to perfec- 
 tion. In the eyes of many, this last may prove no recom- 
 mendation; but if it be regarded as unworthy of the 
 character of a true man of science, voluntarily to abandon 
 that most precious heritage of a genuine philosopher, an 
 open mind, Penny atoned for his sins by many beautiful 
 investigations, the most important of which are perhaps 
 his determinations of atomic weights, determinations 
 which even to-day rank among the most reliable. 
 
 Thomas Graham was the son of a Glasgow manu- 
 facturer, and was born towards the end of the year 1805. 
 He was educated in the Glasgow High School, and after- 
 wards at the university there. His university career lasted 
 an unusually long time ; for entering when he was four- 
 teen years of age, he did not graduate until he had reached 
 the mature age of twenty-one. I am well aware that to an 
 Oxford or Cambridge ' man,' the age of fourteen appears a 
 ridiculously early one at which to enter the university; 
 but in many cases, as for instance in that of a late 
 president of the Royal Society, Lord Kelvin, it is amply 
 justified in its results. There are many boys who 
 
58 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 develop early, and whom it is unfair to measure by the 
 uniform standard of a public school. 
 
 Graham's teacher of chemistry was Dr. Thomas 
 Thomson, a man of European reputation. It was in his 
 textbook of chemistry that Dalton's atomic theory was 
 published, before its author had committed his own ideas 
 to the press ; and he was a man who maintained the 
 liveliest interest in his science, and whose teaching was 
 most stimulating. His teacher of physics, Professor 
 Meikleham, was also, I have heard, an attractive lecturer ; 
 and during his student career, Graham devoted much 
 attention to physics and to mathematics. At the end 
 of his student career, however, Graham had an unfortu- 
 nate difference of opinion with his father, who had 
 designed him for the Church ; with that reserve which is 
 frequently a characteristic of the Scottish nature, neither 
 had made the other aware of his wishes in the choice of 
 a profession ; and having made the discovery, with that 
 'dourness,' also characteristic of the race, neither would 
 yield up his will to the other. Graham therefore left his 
 native city, and pursued his studies in Edinburgh, kept 
 from want . by the self-sacrifice of his mother and his 
 sister Margaret, for his father had cut off supplies. 
 There he studied with Dr. Hope, the discoverer of stron- 
 tium, working diligently the while at mathematics and 
 physics, and so preparing himself for his life-work. Before 
 his student days were over, however, he had begun to 
 earn a little money ; and it is recorded that the first six 
 guineas which he earned were spent in presents for his 
 mother and sister. 
 
 Having returned to Glasgow, and started a small private 
 laboratory, it was not long before he was asked to become 
 lecturer in the Mechanics' Institute, taking the place of 
 Dr. Clark, the inventor of the process for softening water, 
 who had been appointed to the Chair of Chemistry at 
 
THE GREAT LONDON CHEMISTS 59 
 
 Aberdeen. And in 1830, he succeeded Ure, the author 
 of the Dictionary of Chemistry, as professor in 'The 
 Andersonian University/ an institution which had been 
 founded in rivalry to the University of Glasgow, towards 
 the end of the eighteenth century. 
 
 In 1837, Edward Turner, the Professor of Chemistry 
 at the then newly founded University of London, now 
 University College, died ; and Graham was chosen from 
 among many candidates as his successor. He was much 
 elated at the change, and in a letter to my grandmother 
 (for he was an intimate friend of the family), he tells 
 her that he has suddenly risen to affluence, being in 
 receipt of the fees of no fewer than 400 students who 
 attended his lectures ! 
 
 Graham was neither a fluent nor an elegant lecturer ; 
 but his accuracy, his conscientiousness, the philosophical 
 method in which he treated his subject, and his en- 
 thusiasm for his science are said to have proved very 
 attractive to his audience, and without doubt contributed 
 to fill his classroom. The same characteristics are to be 
 noted in his textbook, which I venture to think is the 
 best textbook on chemistry ever written, although it is 
 now completely out of date. No longer republished in 
 English, it still survives in Germany, under the name 
 of ' Graham-Otto.' 
 
 Until 1854, Graham retained his Chair at University 
 College ; but in that year, Sir John Herschel resigned his 
 office as Master of the Mint, and Graham was chosen to 
 occupy that position, held by so many men of eminence, 
 foremost among whom was Sir Isaac Newton. During 
 his tenure of the office, Graham's conscientiousness proved 
 a sore thorn in the side of the minor officials ; and he had 
 a hard struggle to introduce necessary reforms. His 
 strength of character, however, stood him in good stead ; 
 and after some years of active combat, he left the field 
 
60 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 victorious, with leisure to resume the scientific work 
 which the state of warfare had interrupted. In this 
 office he remained until his death, which took place in 
 1869. 
 
 Unlike Davy, Graham was of a modest and retiring 
 disposition. His gentleness endeared him to all those 
 whom he admitted within the circle of his friends ; and 
 his calm judgment rendered him an invaluable counsellor. 
 Yet he received his full meed of honour ; he was the first 
 president of the Chemical Society ; a Fellow of the Royal 
 Society; the 'Keith' Medallist of the Royal Society of 
 Edinburgh; he twice received a Royal Medal of the 
 Royal Society of London, and in 1862 the Copley Medal, 
 given as the reward of a life successfully devoted to 
 scientific discovery ; he was a Corresponding Member of 
 the Institute of France; and he received from that 
 august body the Prix JecJcer. 
 
 Graham's scientific work admits of division into two 
 groups, one relating to the physical behaviour of gases 
 and liquids, and the other to the constitution of salts. 
 Besides papers on these subjects, he published a number 
 of miscellaneous papers. 
 
 In the second of these groups, his earliest communica- 
 tion was on the existence of compounds containing 
 alcohol of crystallisation, analogous to the well-known 
 water of crystallisation. The analogy between water and 
 alcohol was thus shown ; an analogy which, in the hands 
 of his successor Williamson, played an important part in 
 the development of modern views on the constitution of 
 the carbon compounds, and indirectly on the whole of 
 chemistry. In 1833, Graham published his remarkable 
 memoir on the phosphoric acids, in which he argued that 
 as alcohol could replace water in hydrated salts, so water 
 could replace bases, in such salts as the phosphates. 
 The acids of phosphorus had previously been a puzzle to 
 
THE GREAT LONDON CHEMISTS 61 
 
 chemists. Graham proved that orthophosphoric acid 
 consists of a compound of the anhydride, P 2 5 , with 
 three molecules of water, and that each molecule is 
 capable of replacement by the oxide of such a metal as 
 sodium ; that pyrophosphoric acid may be regarded as 
 composed of a molecule of anhydrous phosphoric acid 
 with two molecules of water, each of which is replaceable 
 by an oxide; and that metaphosphoric acid is to be 
 represented as a compound of one molecule of anhydride 
 with one molecule of .water. The general term, which 
 came to be used for this behaviour of acids was basicity, 
 and an acid was termed monobasic, dibasic, or tribasic, 
 according as it was capable of uniting with one, two, or 
 three molecules of base; yet it might contain the same 
 anhydrous oxide in each case. These views of Graham's 
 made it possible to account for the fact, at that time most 
 mysterious, that on mixing nitrate of silver, with its 
 neutral reaction, with alkaline phosphate of sodium, an 
 acid liquid was the result. These experiments of Graham's 
 paved the way for the later theory, that acids are salts of 
 hydrogen. In Graham's language, the three phosphoric 
 acids were ' terphosphate, biphosphate, and phosphate of 
 water ' ; for he understood by the term ' phosphoric acid ' 
 what we nowadays name phosphoric anhydride. The word 
 phosphate, however, is now applied to the group P0 4 , 
 and hence the name phosphates of hydrogen. Graham 
 was the first to recognise that (to quote his own words) 
 ' when one of these compounds (the phosphoric acids) 
 is treated with a strong base, the whole or a part of the 
 water is supplanted, but the amount of base in combina- 
 tion with the acid remains unaltered! We should now 
 say, ' the whole or a part of the hydrogen of the acid is 
 supplanted, but the total number of atoms of hydrogen 
 plus metal in the salt remains'unaltered.' 
 
 Continuing the train of ideas aroused by his researches 
 
62 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 on the phosphoric acids, Graham next advanced the sug- 
 gestion that certain salts may be substituted, molecule for 
 molecule, for water of crystallisation. Thus, sulphate of 
 zinc ordinarily crystallises with seven molecules of water, 
 forming the heptahydrate, ZnS0 4 .7H 2 0. It is possible to 
 replace one of these molecules of water with a mole- 
 cule of potassium sulphate, obtaining the double salt, 
 ZnS0 4 .K 2 S0 4 .6H 2 0. It appeared, too, with this and 
 similar salts, that six molecules of water may be expelled 
 at a lower temperature than the seventh, which may be 
 supposed to be the one which is replaced by the potassium 
 sulphate in the double salt. 
 
 Experiments were also made on the heat evolved on 
 neutralising bases with acids, and on the solution of salts 
 in water. Such experiments on salt were carried on until 
 1843. 
 
 But Graham had all the while another set of re- 
 searches in progress, in which he attempted to arrive 
 at some definite knowledge regarding the constitution of 
 matter. Recognising that the gaseous state represents 
 matter in a simpler condition than that of liquid or solid, 
 his experiments were largely directed towards elucidating 
 the properties of gases. These experiments were started 
 in 1836. From an observation of Doebereiner's, that in a 
 cracked cylinder, containing hydrogen, and standing over 
 water, more gas escaped than entered, so that the level of 
 the water rose in the cylinder, Graham was led to make 
 his experiments on the diffusion of gases, and also on the 
 rate of the escape of gases through narrow openings. 
 Both sets of experiments led to the same law, viz. that 
 the rates of escape are inversely proportional to the square 
 roots of the densities of the gases. Under equal physical 
 conditions, hydrogen moves four times as quickly as 
 oxygen, which is sixteen times as heavy as the former. 
 And since the densities are proportional to the weights of 
 
THE GREAT LONDON CHEMISTS 63 
 
 the molecules, it follows that a molecule of hydrogen 
 moves through space four times as rapidly as a molecule 
 of oxygen. This law was confirmed by measurements 
 made on many other gases. These experimental re- 
 searches of Graham's have been one of the chief supports 
 of the kinetic theory, devised long afterwards, on the 
 assumptions that the pressure of gases is due to the im- 
 pacts of their molecules on the walls of the containing 
 vessel, and that their temperature is to be ascribed to the 
 rate of motion of the molecules. 
 
 Much later, in 1849, Graham investigated the rate of 
 flow of gases through narrow tubes, and obtained results 
 which have also been found of incalculable service to the 
 theory of gaseous matter. 
 
 A few years later, in 1851 and 1852, Graham published 
 investigations on the diffusion of liquids, a subject follow- 
 ing close on the lines of his former work on the diffusion 
 of gases. His plan of experiment was as simple as it was 
 well adapted to furnish the information sought. A wide- 
 mouthed bottle was filled with the solution of a salt, and 
 placed inside a wider jar; the jar was then carefully filled 
 with water, care being taken not to disturb the level of 
 the solution in the bottle. The apparatus was then left 
 to itself for a considerable time. It was found that the 
 salt did not stay within the bottle, but gradually escaped 
 into the jar. The amount escaping in different times and 
 at different temperatures was measured. 
 
 Experiments made on a great variety of substances soon 
 revealed the fact that some substances escape much more 
 rapidly than others. For instance, Graham found that 69 
 parts of sulphuric acid, 58 of common salt, 26 of 
 sugar, 13 of gum-arabic, and only 3 of egg-albumen 
 escape in equal times, other circumstances being equal. 
 Some other substances, such as potassium and ammonium 
 chlorides, potassium and ammonium nitrates, magnesium 
 
64 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 and zinc sulphates, take equal times to diffuse. More- 
 over, some salts may be decomposed into their constitu- 
 ents by diffusion ; among these are ordinary alum, where 
 the more easily diffusible potassium sulphate passes away 
 from the less quickly diffusing aluminium sulphate. 
 And even potassium sulphate itself shows signs of 
 yielding potassium hydroxide and sulphuric acid on 
 diffusion. 
 
 It was known that a solution, placed on the outside of 
 a porous diaphragm, on the inside of which was pure 
 water, tended to pass through the septum; and if the 
 inner vessel, containing the water, were fitted with a 
 pressure-gauge, the pressure would rise in the interior. 
 This pressure had been named ' osmotic pressure/ 
 Graham attempted to connect this phenomenon with 
 diffusion, but found that ordinary salts, as well as sugar, 
 tannin, alcohol, urea, and similar bodies, had little effect 
 in raising pressure. On the other hand, osmotic pheno- 
 mena were well marked when strong acids, or tartaric, 
 citric, or acetic acids, were present in the cell. In all 
 cases of osmotic pressure, it was found that the porous cell 
 was strongly attacked, and Graham was inclined to ascribe 
 the phenomenon to chemical action. It is in all pro- 
 bability due to the fact that such diaphragms present 
 very little of what we now term 'semi-permeability' to 
 the salts in question. 
 
 From the year 1852 to the year 1861, Graham's duties 
 at the Mint absorbed nearly all his time, so that there is 
 a long gap in the series of his publications. But in the 
 latter years he published the results of experiments on 
 the transpiration of liquids, a subject which has lately 
 been successfully treated by numerous investigators. 
 And with his practical bias, Graham devised a plan of 
 applying osmotic phenomena to the separation of 
 crystalline substances, which easily pass through a 
 
THE GREAT LONDON CHEMISTS 65 
 
 porous diaphragm, such as the common acids and salts, 
 from ' colloid ' or gum-like substances, the rate of passage 
 of which is much slower. Especially useful was this pro- 
 cess for the separation of poisons such as the alkaloids 
 and metallic salts from the contents of the stomach in 
 medico-legal inquiries. 
 
 Time allows me only to mention Graham's most in- 
 teresting experiments on the absorption of gases by 
 metals, and the passage of hydrogen through a thin sheet 
 of palladium; the retention of hydrogen by palladium 
 led him to surmise that the metallic substance was a 
 true alloy of palladium, with metallic hydrogen, and to 
 form the theory that hydrogen itself should be ranked 
 among the metals. He even tried to impress the view by 
 terming the element ' hydrogenium,' in consonance with 
 the nomenclature of most metals. 
 
 But I must conclude this imperfect sketch of Graham's 
 work, trusting that what I have said may induce some of 
 my readers to make acquaintance with it at first hand. 
 Graham's conscientiousness in all he did, his enthusiasm, 
 and his great ability render his style in writing a most 
 fascinating one; and his papers will always remain a 
 model to those who publish on similar subjects. He 
 possessed a truly philosophical mind ; and in this he more 
 resembled Boyle, than Cavendish or Davy. Indeed, it 
 may be guessed that if Graham had lived in the seven- 
 teenth century, and Boyle in the nineteenth, the results of 
 their labours would not have differed very widely from 
 those which bear their respective names. 
 
 Contrasting Graham's character with those of Cavendish 
 and Davy, it may be said that while Cavendish carried his 
 devotion to science to such a height that it deprived him of 
 the ordinary pleasures of a human being, and while Davy 
 took perhaps too prominent a part in the world of fashion 
 
 E 
 
66 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 to escape the accusation of 'playing to the gallery/ 
 Graham pursued a happy mean, beloved by the few whom 
 he chose for his intimate friends, and esteemed and 
 respected by all. Of him, as of Faraday, it might have 
 been said with no shade of misgiving, ' He was a good and 
 a true man.' 
 
JOSEPH BLACK: HIS LIFE AND WOKK 
 
 THERE are some natures so happily constituted that they 
 escape many of the trials which beset most men. Marcus 
 Aurelius thanked his adopted father for having taught 
 him the advantages of ' a smooth and inoffensive temper ; 
 constancy to friends, without tiring or fondness; being 
 always satisfied and cheerful ; reaching forward into the 
 future, and managing accordingly ; not neglecting the least 
 concerns, but all without hurry, or being embarrassed.' 
 Such a character had Joseph Black. Dr. Robison, the editor 
 of his lectures, his successor in Glasgow University, and his 
 biographer, wrote : ' As he advanced in years his coun- 
 tenance continued to preserve that pleasing expression of 
 inward satisfaction, which, by giving ease to the beholder, 
 never fails to please. His manner was perfectly easy and 
 unaffected and graceful. He was of most easy approach, 
 affable, and readily entered into conversation, whether 
 serious or trivial. His mind being abundantly furnished 
 with matter, his conversation was at all times pertinent 
 and agreeable. He was a stranger to none of the elegant 
 accomplishments of life.' His friend Dr. Ferguson said of 
 him : ' As Dr. Black had never anything for ostentation, 
 he was at all times precisely what the occasion required , 
 and no more. Never did any one see Dr. Black hurried at 
 one time to recover matter which had been improperly 
 neglected on a former occasion. Everything being done in 
 its proper season and place, he ever seemed to have leisure 
 in store ; and he was ready to receive his friend or acquaint- 
 ance, and to take his part with cheerfulness in any con- 
 
 67 
 
68 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 versation that occurred.' His successor, Dr. Thomas 
 Thomson, found Dr. Robison's estimate of Black's char- 
 acter so just that he appropriated it almost verbatim in 
 his History of Chemistry without the formality of quota- 
 tion marks. 
 
 His pupil, Henry Brougham, one of the founders of the 
 college in which I have the honour to hold a chair, por- 
 trays him in his Philosophers of the time of George III. 
 as 'a person whose opinions on every subject were marked 
 by calmness and sagacity, wholly free from both passion 
 and prejudice, while affectation was only known to him 
 from the comedies he might have read. His temper in 
 all the circumstances of life was unruffled. . . . The sound- 
 ness of his judgment on all matters, whether of literature 
 or of a more ordinary description, was described by Adam 
 Smith, who said he " had less nonsense in his head than 
 any man living." ' Brougham, writing as an old man, 
 said: 'I love to linger over these recollections, and to 
 dwell on the delight which I well remember thrilled me 
 as I heard this illustrious sage detail the steps by which 
 he made his discoveries, illustrating them with anecdotes 
 sometimes recalled to his mind by the passages of the 
 moment, and giving them demonstration by performing 
 before us the many experiments which had revealed to 
 him first the most important secrets of nature. Next to 
 the delight of having actually stood by him when his 
 victory was gained, we found the exquisite gratification of 
 hearing him simply, most gracefully, in the calm spirit of 
 philosophy, with the most perfect modesty, recount his 
 difficulties, and how they were overcome; open to us the 
 steps by which he had successfully advanced from one 
 part to another of his brilliant course ; go over the same 
 ground, as it were, in our presence, which he had for the 
 first time trod so many long years before ; hold up per- 
 haps the very instruments he had then used, and act over 
 
JOSEPH BLACK: HIS LIFE AND WORK 69 
 
 again the same part before our eyes which had laid the 
 deep and broad foundations of his imperishable renown. 
 Not a little of this extreme interest certainly belonged to 
 the accident that he had so long survived the period of 
 his success that we knew there sat in our presence the 
 man now in his old age reposing under the laurels won 
 in his early youth. But take it altogether, the effect was 
 such as cannot well be conceived. I have heard the 
 greatest understandings of the age giving forth their 
 efforts in its most eloquent tongues have heard the com- 
 manding periods of Pitt's majestic oratory the vehe- 
 mence of Fox's burning declamation have followed the 
 close compacted chain of Grant's pure reasoning been 
 carried away by the mingled fancy, epigram, and argu- 
 mentation of Plunket; but I should without hesitation 
 prefer, for mere intellectual gratification (though aware 
 how much of it is derived from association) to be once 
 more allowed the privilege which I in those days enjoyed 
 of being present while the first philosopher of his age was 
 the historian of his own discoveries, and be an eye-witness 
 of those experiments by which he had formerly made 
 them, once more performed with his own hands.' 
 
 Truly, Scotland in the last half of the eighteenth 
 century was the home of many great men. Adam Smith, 
 the first political economist ; David Hume, the historian ; 
 James Hutton, the geologist; and James Watt, the 
 engineer : all these were intimate friends of Black's, and 
 each in his way was an originator of the first order. 
 And it is my pleasant task to present to you an account 
 of Black's discoveries and their consequences, and to 
 attempt to show that his work began a new epoch for 
 chemistry and physics. 
 
 There is little to tell of Black's early history; nor, 
 indeed, was his life even remotely adventurous. His 
 career may be told in a few words. 
 
70 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Joseph Black was born on the banks of the Garonne, 
 near Bordeaux, in 1728. His father, John Black, was a 
 native of Belfast, descended from a Scottish family which 
 had settled there; he resided at Bordeaux, where he 
 carried on a business in wine ; he was an intimate friend 
 of President Montesquieu. Joseph was one of thirteen 
 children, of whom eight were sons. In 1740, at the age 
 of twelve, he was sent to school in Belfast ; and like many 
 other boys of the north of Ireland, he crossed to Glasgow to 
 attend its University, for in those days, of course, Queen's 
 College, Belfast, had not been founded. This was in the 
 year 1746. Dr. Robison mentions letters from Mr. Black 
 to his son Joseph, from which it would appear that he was 
 in every respect a satisfactory son and a diligent student. 
 He received a general education ; we find, at least, that he 
 could write good Latin ; and he was taught ethics by 
 Adam Smith. His leanings for natural science, however, 
 were probably encouraged by his intimate friendship with 
 the son of the Professor of Natural Philosophy, Dr. Robert 
 Dick, later successor to his father in the chair, who, un- 
 fortunately, occupied it only a few years, for he was early 
 cut off by death. Black also owed much to Cullen, of whom 
 a very interesting account is given by Thomas Thomson 
 in his History. Cullen was Lecturer in Chemistry in 
 the University of Glasgow from 1746 to 1756 ; and in' 
 1751 he was appointed Professor of Medicine; at that time, 
 and, indeed, until Thomas Thomson taught chemistry, 
 that subject was taught only by a lecturer. Thomson 
 attributes to Cullen a singular talent for arrangement, dis- 
 tinctness of enunciation, vivacity of manner, and profound 
 knowledge of his science in short, enthusiasm qualities 
 which made him adored by his students. He took 
 especial pains to gain their friendship by frequent social 
 intercourse with them, and no doubt early recognised 
 Black's great promise. Cullen's single contribution to 
 
JOSEPH BLACK: HIS LIFE AND WORK 71 
 
 chemico-physical literature dealt with the boiling of ether 
 on the reduction of pressure, and its growing cold during 
 the process. The reason of this behaviour, however, was 
 later discovered by Black, for Cullen confined himself to 
 recording the observation. It was not long before Black 
 rendered help to Cullen as his assistant ; and Black's name 
 was frequently quoted by Cullen in his lectures as an 
 authority for certain facts. 
 
 Black's methodical habits led him to keep a sort of 
 commonplace book, in which not merely the results of 
 his experimental work was entered, but also notes on 
 medicine, jurisprudence, or matters of taste; and he 
 practised 'double entry/ for he also kept separate journals 
 in which these notes were distributed according to their 
 subjects. From these notebooks the dates of his most 
 important discoveries can be traced. 
 
 Chemistry, in these days, was handmaid to medicine ; 
 the influence of the iatro-chemists, founded by Paracelsus, 
 still held its sway, although certain bold investigators 
 among them Boyle, Mayow, and Hales a century before, 
 had shaken themselves free from its thraldom. And the 
 lectureship on chemistry in Glasgow was regarded as a 
 step to a more remunerative position, and was held, along 
 with the Crown professorship of medicine, by Cullen from 
 1751 to 1756. It was probably owing to Cullen's advice 
 that Black went to Edinburgh in 1750 or 1751 to finish 
 his medical studies ; perhaps another reason may be found 
 in his having had a cousin in the University, Mr. James 
 Russel, as Professor of Natural Philosophy, with whom he 
 lived. There he took the degree of doctor of medicine in 
 1754. It is true that he might have graduated in Glasgow 
 three years earlier ; but no doubt his thoroughness made 
 him wish to offer a thesis worthy of praise, and it was 
 this thesis which established his reputation. More of 
 this hereafter. 
 
72 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 In 1756 Dr. Cullen was called to fill the Chair of 
 Chemistry in Edinburgh, and Black, who had been prac- 
 tising as a physician since he had graduated, was called to 
 succeed him in the Chair of Anatomy and the lectureship 
 in Chemistry; for his reputation in the subject which he 
 had made his own was even then a high one. Black did 
 not retain the Chair of Anatomy for long, however ; his 
 tastes lay more in the direction of medicine ; and with the 
 concurrence of the University he and the professor of 
 medicine exchanged chairs. While he held these offices 
 he also engaged in medical practice ; and Robison says that 
 his countenance at that time of life he was then about 
 thirty-two was equally engaging as his manners were 
 attractive ; and in the general popularity of his character 
 he was in particular a favourite with the ladies. No one, 
 so far as we know, was singled out by his preference ; and 
 to the end of his days he remained unmarried. It appears 
 that the ladies regarded themselves as honoured by his 
 attentions, and we are told that these attentions were not 
 indiscriminately bestowed, but exclusively on those who 
 evinced a superiority in mental accomplishments or 
 propriety of demeanour, and in grace and elegance of 
 manners. 
 
 In 1766, Dr. Cullen exchanged the Chair of Chemistry 
 at Edinburgh for that of Medicine ; and with one accord 
 University and town united in calling Dr. Black to the 
 vacant chair. Indeed, in 1756, he had been recom- 
 mended for the chair by the University; but the Town 
 Councillors who were the electors did not agree with 
 the recommendation, and Cullen was appointed. Now, 
 however, unanimity prevailed, and Black removed to 
 Edinburgh, where he spent the rest of his days. 
 
 From this date, he devoted himself to tuition, and 
 spared no pains to make his lectures attractive and 
 useful. He illustrated them by numerous experiments. 
 
OF 
 
 JOSEPH BLACK: HIS LIFE AND WORK 73 
 
 Robison tells us that, ' while he scorned the quackery of 
 a showman, the simplicity, neatness, and elegance with 
 which they were performed were truly admirable/ And 
 Brougham also praises his manipulation. 'I have seen 
 him/ he writes, 'pour boiling water or boiling acid from 
 one vessel to another, from a vessel that had no spout 
 into a tube, holding it at such a distance as made the 
 stream's diameter small, and so vertical that not a drop 
 was spilt. The long table on which the different pro- 
 cesses had been carried on was as clean at the end of the 
 lecture as it had been before the apparatus was planted 
 upon it. Not a drop of liquid, not a grain of dust 
 remained/ 
 
 Black had a profound influence on the attitude of the 
 Edinburgh public towards science. The reputation which 
 he established as a lecturer induced many to attend his 
 lectures without any particular wish to learn chemistry, 
 but merely to enjoy an intellectual treat ; and it became 
 the fashion to hear him. 
 
 The study of the chemistry of gases, after Black's dis- 
 covery of carbonic acid, made rapid progress; but Black 
 did not take part in its advance. His health had never 
 been good; he was very subject to dyspepsia; and on 
 several occasions his lungs or his bronchise appear to have 
 narrowly escaped being affected, for he was troubled with 
 spitting of blood. But he had learned the lesson yva>0e 
 o-eavrov know thyself; and he regulated his exercise and 
 his diet with the result that he lived a quiet, and a fairly 
 long life. 'Happy is the nation that has no history'; 
 and Dr. Black's uneventful life was passed in happiness. 
 He held his chair for more than thirty years, and grew 
 old gracefully, living amongst many intimate friends. 
 He at one time acquired a reputation for parsimony ; but 
 Brougham, while suggesting a reason for this report, 
 namely that he kept a pair of scales on his study table 
 
74 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 with which he used to weigh the guineas paid in as fees, 
 defends this perhaps somewhat curious practice, and 
 refutes the imputation ; and Robison, who also alludes to 
 it, states in a footnote that he could give more than one 
 or two instances in which a great part of Black's fortune 
 was at risk for a friend. 
 
 As his strength decreased, the care of his health 
 occupied more and more of his attention; he became 
 more and more abstemious in his diet. One of his 
 intimate friends, Dr. Ferguson, gives the following account 
 of his death, one worthy of such a calm and placid philo- 
 sopher: 'On the 26th November 1799, and in the 
 seventy- first year of his age, he expired, without any 
 convulsion, shock, or stupor to announce or retard the 
 approach of death. Being at table, with his usual fare, 
 some bread, a few prunes, and a measured quantity of 
 milk, diluted with water, and having the cup in his hand 
 when the last stroke of his pulse was to be given, he had 
 set it down on his knees, which were joined together, and 
 kept it steady with his hand in the manner of a person 
 perfectly at ease, and in this attitude expired, without 
 spilling a drop, and without a writhe in his countenance, 
 as if an experiment had been required to show his friends 
 the facility with which he departed.' 
 
 He left more money than any one thought he could 
 have acquired in the course of his career. His will was a 
 somewhat fantastic one ; he divided his property into ten 
 thousand shares ; and he distributed it among numerous 
 individuals in shares or in fractions of shares, according to 
 his conception of their needs or deserts. 
 
 A tale is told in Kay's Edinburgh Portraits of Black and 
 Hutton, who were almost inseparable cronies. Having had 
 a disquisition as to the waste of food, it occurred to them 
 that while testaceous marine animals were much esteemed 
 as an article of diet, those of the land were neglected ; 
 
JOSEPH BLACK: HIS LIFE AND WORK 75 
 
 they resolved to put their views in practice, and having 
 collected a number of snails, had them cooked, and sat 
 down to the banquet. Each began to eat very gingerly ; 
 neither liked to confess his true feelings to the other. 
 'Dr. Black at length broke the ice, but in a delicate 
 manner, as if to sound the opinion of his messmate: 
 "Doctor," he said, in his precise and quiet manner, 
 "Doctor, do you not think that they taste a little a 
 very little queer?" "Queer, queer indeed! tak them 
 awa', tak them awa' ! " vociferated Dr. Hutton, start- 
 ing up from table, and giving vent to his feelings of 
 abhorrence.' 
 
 The portraits of the subject of this biography reveal 
 Black as possessing a calm, contemplative nature; but 
 Kay's caricatures indicate that he could take a some- 
 what humorous view of life, and perhaps might even 
 display a vein of caustic sarcasm. A portrait of him 
 while lecturing may well have been sketched, we may 
 suppose, while he was making scathing comments on 
 the objections raised by a German chemist named Meyer 
 to his doctrine of causticity, which ' that person,' as 
 Brougham tells us, ' explained by supposing an acid, called 
 by him acidum pingue, to be the cause of alkaline mild- 
 ness. The unsparing severity of the lecture in which 
 Black exposed the ignorance and dogmatism of this 
 foolish reasoner cannot well be forgotten by his hearers.' 
 It appears to me, however, that Meyer's theory cannot 
 have been correctly stated by Brougham (for it is remark- 
 ably like Black's own explanation), or must have been 
 misunderstood by Black. Another of Kay's portraits 
 exhibits Black and Hutton, under the title of 'The 
 Philosophers ' ; and here again the caricaturist has made 
 it obvious that Black could appreciate a joke. A third 
 portrait represents him taking a gentle walk ; it conveys 
 an idea of his appearance in his fifty -ninth year. 
 
76 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 The portrait of Dr. Cullen, Black's predecessor both 
 in Glasgow and Edinburgh, and his life-long friend, 
 is also given by Kay. Cullen died in 1790, at the age 
 of eighty-one. 
 
 In the olden days it was considered quite as marvellous 
 that a gas could be made to occupy a small volume, or 
 that ' air ' could be produced in quantity from a stone, as 
 that an Arabian 'djinn' of enormous size and ferocious 
 mien could issue from a bottle, as related in the ' Tale of a 
 Fisherman,' one of the charming stories of the Arabian 
 Nights Entertainments. It is true that in the middle of 
 the seventeenth century Robert Boyle had enunciated his 
 famous discovery, ' Touching the Spring of the Air ' ; in 
 which he proved that the greater the pressure to which a 
 gas is exposed the smaller the volume it will occupy. 
 But however great the pressure, Boyle's air remained air. 
 It might have been thought that the boiling of water into 
 steam should have convinced men that a liquid, at least, 
 could be changed into a gas; but the fact that steam 
 changed back to water probably prevented attention being 
 paid to its comparative large volume while hot. It was 
 Black's discovery of the production of carbonic acid gas 
 from marble, or as he named it, 'fixed air,' which first 
 directed notice to this possibility of the production of a 
 gas from a solid; and further, the peculiar property of 
 this gas its power of being fixed was one which com- 
 pletely differentiated it from ordinary air. Stephen Hales 
 the botanist, it is true, had distilled many substances of 
 vegetable, animal, and mineral origin; among them he 
 treated many which must have produced impure hydrogen, 
 marsh-gas, carbonic acid gas, and oxygen; but Hales 
 contented himself with measuring the volume of gases 
 obtained from a known weight of material, without con- 
 cerning himself about their properties. And as the result 
 of many experiments, he concluded that ' our atmosphere 
 
JOSEPH BLACK: HIS LIFE AND WORK 7*7 
 
 is a chaos, consisting not only of elastick, but also of 
 unelastick air-particles, which in plenty float in it, as well 
 as the sulphureous, saline, watry, and earthy particles, 
 which are no ways capable of being thrown off into a 
 permanently elastick state, like those particles which 
 constitute true permanent air/ This was the current 
 belief as regards the nature of air. 
 
 The cause which gave rise to Black's famous research is 
 a curious one. Sir Robert Walpole, as well as his brother 
 Horace, afterwards Lord Walpole, were troubled with the 
 stone. They imagined that they had received benefit 
 from a medicine invented by a Mrs. Joanna Stephens; 
 and through their influence she received five thousand 
 pounds for revealing the secret, which was published in 
 the London Gazette on the 19th June 1739. It was 
 described as follows : 
 
 'My medicines are a Powder, a Decoction, and Pills. 
 The powder consists of Egg-shells 1 and Snails, 2 both 
 calcined. The decoction is made by boiling some Herbs 3 
 (together with a Ball, which consists of Soap, 4 Swines'- 
 Cresses, burnt to a Blackness, and Honey) in water. The 
 Pills consist of Snails calcined, Wild Carrot seeds, Burdock 
 seeds, Ashen Keys, Hips and Hawes, all burnt to a Black- 
 ness, Soap and Honey.' 
 
 Dr. Cullen and his colleagues held opposing views as to 
 the efficacy of such quaint and caustic remedies ; and it 
 was with the object of discovering a ' milder alkali,' and 
 bringing it into the service of medicine, that Black began 
 
 1 ' Egg-shells and Snails calcined in a crucible surrounded with coal for 
 8 hours. Then left in an earthenware pan to slake in a dry room for 2 
 months. The Shells thus become of a milder taste, and fall into powder.' 
 
 2 ' Snails left in a crucible until they have done smoaking, then rubbed 
 up in a mortar. Take 6 parts of Egg-shell to 1 of Snail-powder. Snails 
 ought only to be prepared in May, June, July, and August.' 
 
 3 ' Herbs of decoction : Green Chamomile, Sweet Fennel, Parsley, and 
 Burdock ; leaves or roots.' 
 
 4 'Soap: Best Alicant Soap.' 
 
78 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 his experiments on magnesia. They are described in a 
 paper entitled ' Experiments upon Magnesia Alba, Quick- 
 lime, and some other Alcaline Substances'; it was the 
 chemical contents of his thesis for the degree of M.D., 
 which he took at Edinburgh in 1754 ; he had been making 
 the experiments since 1752. The actual thesis was in 
 Latin : ' De Humore Acido a Cibis orto, et Magnesia Alba ' ; 
 the pamphlet was published in the following year. 
 
 The medicines in vogue as solvents of the urinary cal- 
 culus were all caustic ; the lapis infernalis, or caustic 
 potash, and the ley of the soap-boilers, or caustic soda. 
 These substances are made from mild alkali, or carbonates, 
 by boiling their solutions with slaked lime, itself produced 
 by slaking quicklime with water. Now quicklime is 
 formed by heating lime-stone in the fire; it thereby 
 acquires its burning properties, or causticity ; and this it 
 was supposed to derive from the fire, of which it absorbed, 
 as it were, the essence. The act of boiling the mild 
 alkalies with lime was supposed to result in a transference 
 of this educt of fire to the alkalies, which themselves 
 became caustic, Lime-water, or a solution of caustic lime 
 was used as a solvent for the calculus; and it was an 
 attempt to produce a less caustic solvent from Epsom salts 
 that induced Black to begin his researches. 
 
 As his notes show, Black began by holding the old view. 
 He attempted to catch the igneous matter as it escaped 
 from lime, as it becomes ' mild ' on exposure to the air : 
 he appears to have made some experiment with this view ; 
 but his comment was, 'Nothing escapes the cup rises 
 considerably by absorbing air/ Two pages further on in 
 his notebook he records an experiment to compare the 
 loss of weight sustained by an ounce of chalk when it is 
 calcined with its loss when dissolved in ' spirit of salt/ or 
 hydrochloric acid ; and he then evidently began to suspect 
 the reason of ' mildness ' and ' causticity/ 
 
JOSEPH BLACK : HIS LIFE AND WORK 79 
 
 Another memorandum, a few pages later, shows that he 
 had solved the mystery. ' When I precipitate lime by a 
 common alkali there is no effervescence. The air quits 
 the alkali for the lime, but it is not lime any longer, but 
 c.c.c. It now effervesces, which good lime will not.' 
 
 But we must trace the chain of reasoning which led him 
 to come to this conclusion. 
 
 Having prepared ' mild ' magnesia by mixing Epsom 
 salt or sulphate of magnesia with carbonate of potash, or 
 ' pearl- ashes/ he found that it is ' quickly dissolved with 
 violent effervescence or explosion of air by the acids of 
 vitriol, nitre, and of common salt, and by distilled vinegar ' ; 
 that the properties of these salts the sulphate, nitrate, 
 chloride, and acetate of magnesium differ greatly from 
 those of the common alkaline earths; that when boiled 
 with 'salt-ammoniac,' or chloride of ammonium, volatile 
 crystals of smelling-salts were deposited on the neck of 
 the retort, which, on mixing with the chloride of mag- 
 nesium remaining in the retort, reproduced the 'mild' 
 magnesia; that a similar effect is produced by boiling 
 ' mild ' magnesia with ' any calcareous substance ' ; while 
 the acid quits the calcareous salt to unite with the mag- 
 nesia, ' mild ' magnesia is again precipitated on addition of 
 a dissolved alkali. 
 
 On igniting ' mild ' magnesia, it changed into a white 
 powder, which dissolved in acids without effervescence. 
 And the process of ignition had deprived it of seven- 
 twelfths of its weight. Black next turned his attention to 
 the volatile part ; he attempted to restore it by dissolving 
 the magnesia in a sufficient quantity of ' spirit of vitriol ' 
 or dilute sulphuric acid, and separated it again by the 
 addition of alkali. The resulting white powder now effer- 
 vesced violently with acids, and 'recovered all those 
 properties which it had lost by calcination. It had 
 acquired besides an addition of weight nearly equal to 
 
80 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 what had been lost in the fire; and as it is found to 
 effervesce with acids, part of the addition must certainly 
 be air.' 
 
 Black here made an enormous stride ; he had weighed 
 a gas in combination. He argues further : ' It seems there- 
 fore evident that the air was forced from the alkali by the 
 acid, and lodged itself in the magnesia/ We may repre- 
 sent the change diagrammatically thus : 
 
 Magnesia \ x Alkali^-Yitriolated alkali. 
 Spirit of vitriol ' ^ Air->Mild magnesia. 
 
 The next step was to try whether mild magnesia lost 
 the same weight on being mixed with acid as it did when 
 heated in the fire. But owing probably to the solubility 
 of the fixed air in the water, a much less loss was found 
 on dissolving the magnesia (35 grains out of 120) than by 
 heating it (78 grains out of 120). The amount of acid 
 required to expel the fixed air was, however, practically 
 the same as that required to dissolve the magnesia usta, 
 or heated magnesia (267 and 262 grains). 
 
 Turning his attention next to chalk, he dissolved some 
 in muriatic acid, and having precipitated with fixed alkali 
 no difference could be detected between the recovered and 
 the original chalk. He had thus first separated the fixed 
 air from the chalk, and then recombined the two. These 
 experiments led Black to conclude that fixed air must be 
 of the nature of an acid, for it converts quick-lime the 
 acrid earth, as he termed it into crude lime, or mild 
 earth, the mildness being due to its union with fixed air. 
 
 The explanation is thus given of the curious fact that 
 mild magnesia, mixed with lime-water, gives pure water ; 
 for the fixed air leaves the magnesia and unites itself to 
 the lime, and both the magnesia usta and the chalk 
 which are formed are insoluble in water. And the action 
 
JOSEPH BLACK: HIS LIFE AND WORK 81 
 
 of quick-lime in causticising alkali is similarly explained 
 by its removing the fixed air from the alkali, thus render- 
 ing the latter caustic, while itself becoming mild. 
 
 Reasoning further, Black foresaw that caustic alkali, 
 added to Epsom salt or vitriolated magnesia, should give 
 a precipitate of magnesia which should not effervesce with 
 acids, for here fixed air is excluded ; and, also, that caustic 
 alkali should separate from acids lime in the quick state, 
 only united with water. 
 
 Similar experiments of treating chalk with acids and 
 heating it, which had been performed with magnesia, 
 showed similar results. 
 
 But it had yet to be demonstrated that fixed air did not 
 share the properties of ordinary atmospheric air. So 
 Black placed four fluid ounces of lime-water, as well as 
 four ounces of common water, under the receiver of an 
 air-pump, and exhausted the air; air rose from each in 
 about the same quantity ; it therefore appeared that the 
 air which quick-lime attracts is of a different kind from 
 that which is mixed with water. Quick-lime does not 
 attract air when in its most ordinary form, but is capable 
 of being joined to one particular species only, 'which is 
 dispersed through the atmosphere, either in the state of a 
 very subtle powder, or, more probably, in that of an elastic 
 fluid. To this I have given the name of fixed air, and 
 perhaps very improperly ; but I thought it better to use a 
 word already familiar in philosophy than to invent a new 
 name, before we be more fully acquainted with the nature 
 and properties of this substance.' 
 
 The next step was to examine the nature of caustic 
 alkali, and to prove whether it gained weight on being 
 made ' mild.' This was achieved indirectly, by finding the 
 amount of acid required to neutralise the same weight of 
 caustic alkali, and ' salt of tartar ' what we know as 
 potassium carbonate. Six measures of acid were required 
 
 F 
 
82 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 to saturate the former, and five the latter ; and Black was 
 very near the truth ; indeed his error was only about four 
 per cent. He proved, by addition of sulphuric acid, that 
 the caustic alkali contained no lime, and therefore that 
 its causticity was not due to an admixture of that 
 substance. 
 
 To prove that lime-stone, or magnesia, ' loses its air ' 
 when dissolved in an acid, but regains it on addition of a 
 mild alkali, the acid in which the lime was dissolved 
 passing to the alkali, Black added caustic ley to a solution 
 of Epsom salt, the result being a precipitate of magnesia ; 
 this dissolved in vitriol without effervescence, showing 
 that no fixed air had taken part in the change. He also, 
 on adding caustic alkali to a solution of chalk in spirit of 
 salt (or hydrochloric acid), produced lime, which on being 
 dissolved in water produced lime-water, indistinguishable 
 from that produced from quick-lime and water. He goes 
 on to say that ' had we a method of separating the fixed 
 alkali from an acid, without at the same time saturating 
 it with " air " we should then obtain it in a caustic form.' 
 It can be done, it is true, by heating nitre with charcoal, 
 but the alkali is then found saturated with air; and 
 again, by heating the alkali-salts of vegetable acids, the 
 same occurs. Black conjectures that the fixed air must 
 be derived either from the nitre or the charcoal in the 
 first case (indeed it is derived from both, the nitre supply- 
 ing the oxygen to the carbon); and in the second, he 
 remarks that the vegetable acid is not really separated, 
 but rather destroyed by the fire. How nearly he came 
 to the discovery that fixed air is produced from carbon ! 
 
 Such was Black's research on fixed air. And now 
 having shown that a gas can be retained by a solid, and 
 can be made to escape by treatment with acid or by heat, 
 he attacked somewhat later the problem of the cause of 
 this fixation. He discovered it to be due to what he 
 
JOSEPH BLACK: HIS LIFE AND WORK 83 
 
 termed ' latent ' or hidden heat. But his research was not 
 made with this object; the connection of the two was 
 fortuitous, although of a fundamental nature. 
 
 Between the years 1759 and 1763, he formed opinions 
 regarding the quantity of heat necessary to raise equally 
 the temperatures of different substances. Boerhaave 
 imagined that all equal portions of space contain equal 
 amounts of heat, irrespective of the nature of the matter 
 with which they are filled ; and his reason for this state- 
 ment was that the thermometer stands at the same 
 height if placed in contact with objects near each other. 
 Here we have a confusion between heat and temperature ; 
 and this was perceived by Black, for he pointed out that 
 a distinction must be drawn between quantity and inten- 
 sity of heat : the latter being what we now call tempera- 
 ture. He quotes Fahrenheit to show that while equal 
 measures of water at different temperatures acquire a 
 mean temperature when mixed, it requires three measures 
 of quicksilver at a high temperature to convert two 
 measures of water at a low temperature to the mean of 
 the two temperatures; and this corresponds to twenty 
 times the weight of the water. Black expressed this by 
 the statement that the capacity for heat of quicksilver is 
 much less than that of water. 
 
 But before this, in 1757, Black had made experiments 
 leading up to these views. He had noticed that when ice 
 or any solid substance is changing into a fluid, it receives 
 a much greater amount of heat than what is perceptible 
 in it immediately afterwards by the thermometer. A 
 great quantity of heat enters into it without making it 
 perceptibly warmer. Conversely, in freezing water or any 
 liquid, a large amount of heat comes out of it, which again 
 is not revealed by a thermometer. 
 
 He then proceeded to estimate the quantity of heat 
 which had to be absorbed by a known weight of ice in 
 
84 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 order to melfc it. He hung up two globes side by side, 
 about 18 inches apart, in a large empty hall, in which the 
 temperature remained practically constant ; each globe 
 contained 5 ounces ; one of ice at 32 F., the other water 
 at 33. The latter had a delicate thermometer suspended 
 in it. The temperature of the hall was 47 F. In half an 
 hour, the water had attained the temperature 40 F. ; 
 and the ice took ten hours and a half to attain the same 
 temperature, that is, twenty-one times as long as the 
 water. The heat, which the ice absorbed during melting 
 was (40 33) x 21 or 147 units; that is, had it been 
 absorbed by the five ounces of water it would have made 
 it warmer by 147. The temperature of the ice, however, 
 was 8 warmer than its melting-point, after the 21 half- 
 hours ; hence 139 or 140 ' degrees had been absorbed 
 by the melting ice, and were concealed in the water into 
 which it had changed.' 
 
 The method of experiment was next varied. Black 
 weighed a lump of ice, and added it to a weighed quantity 
 of warm water of which the temperature was known. 
 The warm water was cooled to a much lower degree by 
 the melting of the ice, than if it had been mixed with a 
 quantity of water of 32 F., equal in weight to the ice. 
 The quantity of heat absorbed by the ice in melting ap- 
 peared from this second experiment to have been capable 
 of heating an equal quantity of water through 143 F. 
 
 A third experiment was made, in which it was proved 
 that a lump of ice, placed in an equal weight of water at 
 176, lowered the temperature of the water to 32. Now 
 176 32=144 again a similar result. The latent heat 
 of water is therefore about 142 or 143, in Fahrenheit 
 units. The result of the most careful measurements give 
 79*5 centigrade units, which corresponds with 143 units 
 of Fahrenheit's scale. Curiously enough, this fundamental 
 datum has not yet been determined with the accuracy 
 
JOSEPH BLACK: HIS LIFE AND WORK 85 
 
 which is customary nowadays, and it is still uncertain to 
 one seven-hundredth of its value. Black's determination 
 was a remarkably good one, especially if we consider the 
 crude appliances which he used. 
 
 The substance of this research was communicated to 
 the ' Philosophical Club/ or Society of Professors and 
 others in the University of Glasgow in the year 1762, and 
 was expounded yearly by Black in his lectures to his 
 students. 
 
 Black suggested to Irvin, his pupil, and afterwards his 
 successor in the Glasgow chair, to determine the latent 
 heat of fusion of spermaceti and bees'-wax ; and he found 
 that these substances, too, absorb heat, insensible to the 
 thermometer, on assuming the liquid state. In this 
 manner, he made his thesis general. But in attempting 
 to extend it beyond the case of liquids and solids, he went 
 astray. For example, he imagined that the great rise of 
 temperature, which may even reach redness, caused by the 
 hammering of iron by a skilled smith, was due to the 
 ' extrication of the latent heat of the iron by hammering/ 
 He did not realise that heat can be produced from 
 mechanical work; that work can be quantitatively trans- 
 formed into heat; a discovery made more than eighty 
 years later, by Joule, although it had been anticipated by 
 Count Rumford, and by Sir Humphry Davy, in the begin- 
 ning of last century. 
 
 Similar experiments were made by Black on the latent 
 heat of steam, in which he compared the time required for 
 a known weight of water to rise through a definite interval 
 of temperature when exposed to a constant supply of heat 
 with that required to dissipate the water into steam, But 
 his estimate of 830 units required to evaporate one part of 
 water was not so accurate ; the actual figure is 967 units on 
 the Fahrenheit scale. Black cited experiments by Boyle, 
 by Robison, his successor in the Glasgow chair, and by 
 
86 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Cullen, his predecessor, in which the boiling-point of 
 liquids had been found to be lowered by reduction of 
 pressure; he rightly ascribes this to the freer escape of 
 the vapour, and to the absorption of heat by the vapour, 
 and the consequent cooling of the liquid from which it is 
 escaping. 
 
 These conceptions of Black's were utilised by his friend 
 James Watt in' his work on condensers, and, as every one 
 knows, effected a revolution in the structure of steam- 
 engines, and as a consequence in the whole of our indus- 
 trial and social life ; and further, they were developed by 
 many men of science, until in the hands of the masters 
 Joule, Clerk-Maxwell, Rankine, James Thomson, and 
 Kelvin, on the physical side, and of Willard Gibbs, the 
 American, on the chemical side they form the very 
 groundwork of the sister sciences, physics and chemistry. 
 
 Black's great chemical discovery that a gas exists which 
 is clearly not a modification of atmospheric air, seeing it 
 can be ' fixed ' by alkalies and alkaline earths, led the way 
 to ' pneumatic chemistry,' as it was called, and was followed 
 by the discovery of oxygen by Priestley, of nitrogen by 
 Rutherford, of hydrogen by Cavendish and Watt, and of 
 the more recent discoveries of argon and its congeners, all 
 of them constituents of the atmosphere. In fact, the gases 
 of the atmosphere have been discovered entirely by Scots- 
 men and Englishmen. 1 
 
 And Black's proof, that the change of a complex com- 
 pound to simpler compounds, and the building up of a 
 complex compound from simpler ones, can be followed 
 successfully by the use of the balance, has had for its 
 consequence the whole development of chemistry. It is 
 only in the most recent years, since Becquerel observed 
 the effect of uranium ores and salts in discharging an 
 
 1 In justice to the Swede Scheele, it should be said that his discovery 
 of oxygen was contemporaneous with Priestley's. 
 
JOSEPH BLACK: HIS LIFE AND WORK 87 
 
 electroscope, and since Madame Curie discerned one of 
 the causes of the discharge by uranium ore, namely, the 
 existence in it of a new element, radium, and since Ruther- 
 ford and Soddy's isolation of the gases evolved from 
 radium and from thorium, that a new and more sensi- 
 tive instrument has been placed at the disposal of 
 chemists in the electroscope. We are at the beginning of 
 a new era. Every discovery of a new principle of research 
 heralds a new departure; and the compound nature of 
 many of the so-called elements begins to appear from 
 their electrical behaviour, in much the same manner as 
 Black demonstrated the decomposability of compounds in 
 the year 1752. 
 
LORD KELVIN 
 
 ON June 16, 1896, there took place in the University of 
 Glasgow an almost unique ceremony. On that day 
 the jubilee of Lord Kelvin was celebrated ; he had been 
 Professor of Natural Philosophy at Glasgow University 
 for fifty years. The Prince of Wales, now King Edward, 
 sent him a letter of congratulation ; twenty-eight univer- 
 sities, twelve colleges, and fifty- one learned societies 
 sent delegates with addresses, wishing Lord Kelvin many 
 more years of health and happiness, and mentioning in 
 terms of profound admiration his magnificent achieve- 
 ments in the domain of physics. What were these, and 
 why did they deserve and obtain such universal admira- 
 tion ? To answer that question fully would require a 
 much longer space than is at my disposal; but I shall 
 try to give a short sketch of William Thomson's life and 
 work. 
 
 In 1812, James Thomson, William's father, was a teacher 
 in the Royal Academic Institute of Belfast. He was one 
 of the descendants of a number of Scotsmen who emigrated 
 to North Ireland in the seventeenth and eighteenth 
 centuries. He had two sons, James and William, both of 
 whom were born in Ireland, and both of whom became 
 illustrious. When William was eight years old, his father 
 was appointed to the Chair of Mathematics in the Uni- 
 versity of Glasgow. My father was one of his students ; 
 and I remember well his allusions to Professor Thomson's 
 kindliness and sense of humour. 
 
90 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 It was" his habit to cross-examine his students, at the 
 beginning of each lecture, on the subject of the preceding 
 day's work ; and it was customary in his junior class to 
 begin with very elementary questions. One day he asked 
 a certain Highlander : ' Mr. M'Tavish, what do you under- 
 stand by a " point " ? ' The answer was, ' It 's just a dab ! ' 
 Again, Mr. M'Tavish was asked, in the course of the con- 
 struction of some diagram : ' What should I do, Mr. 
 M'Tavish ? ' ' Tak a chalk in your hand/ ' And next ? ' 
 ' Draw a line.' Professor Thomson complied, and pausing, 
 said : ' How far shall I produce the line, Mr. M'Tavish ? ' 
 ' Ad infinitum ! ' was the astounding reply. 
 
 At the mature age of ten William entered the university. 
 His training had been wholly in his father's hands ; Pro- 
 fessor Thomson was clear-sighted enough to recognise that 
 he had two very remarkable sons. They were brought up 
 on Classics and Mathematics, Logic and Philosophy. 
 
 In May 1907, at the annual dinner of the London 
 ' Glasgow University Club,' I had the good fortune to hear 
 Lord Kelvin express his views on education. His theme 
 was the ' University of Glasgow ' ; and he commended the 
 universality of the training which it used to give. By the 
 age of twelve, said he, a boy should have learned to write 
 his own language with accuracy and some elegance; he 
 should have a reading knowledge of French, should be 
 able to translate Latin and easy Greek authors, and should 
 have some acquaintance with German. ' Having learned 
 thus the meaning of words/ continued Lord Kelvin, ' a boy 
 should study Logic/ In his charming discursive style, he 
 went on to descant on the advantages of a knowledge of 
 Greek. ' I never found,' he said, ' that the small amount 
 of Greek I learned was a hindrance to my acquiring some 
 knowledge of Natural Philosophy/ It certainly was not 
 in his case. And it may here be remarked that it is surely 
 a mistake to lay down a hard and fast rule that no youth 
 
LORD KELVIN 91 
 
 should enter a college until he has reached the age of 
 fifteen or sixteen; William Thomson took the highest 
 prizes in Mathematics and Physics before he reached that 
 age. It may be said that his precocity was phenomenal ; 
 no doubt it was; but it is precisely those boys who are 
 unique and unlike their fellows who are of value to the 
 race, and every chance should be given to exceptional 
 talent. 
 
 Although William Thomson spent six years at Glasgow 
 University, he did not graduate : in those days the aim of 
 a student's ambition was not a degree, but the acquisition 
 of knowledge. Before he had reached the age of seventeen, 
 he went to Cambridge, where he passed four years. There 
 the examination system was in full swing; and to the 
 disgrace of the examiners, Thomson was not the ' Senior 
 Wrangler '; he was not regarded as the best mathematician 
 of his year ; and this, in spite of the remark made by one 
 of his examiners, that ' the Senior Wrangler was not fit 
 to cut pencils for Thomson.' It is known that success in 
 this examination depends largely on rapidity in writing 
 and on accuracy of memory, ratter than on originality ; 
 and the tale is told that on Thomson's ' coach/ or tutor, 
 asking him why he had spent so much time in answering a 
 particular question, he replied that he had to think it all 
 out from first principles. ' But it is a problem of your own 
 discovery/ said the coach. Thomson had to confess that 
 he had quite forgotten his own handiwork, and that while his 
 competitor had learned the answer by heart, Thomson had 
 had to rediscover the solution. However, he was successful 
 in gaining the ' Smith's Prize/ a reward for inventiveness 
 rather than memory. That same year, he was elected 
 Fellow of his College, and had an income of about 200, 
 which enabled him to continue his studies in France. 
 
 While at Cambridge, Thomson was not only a student ; 
 he always took a keen interest in music, and was president 
 
92 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 of the Musical Society ; he also carried off the ' Colquhoun 
 sculls ' for his excellence as an oarsman. In those days 
 the science of Cambridge was fettered by the bonds which 
 Newton had imposed. It is unfortunate, though perhaps 
 natural, that to the advent of a great man a period of 
 stagnation succeeds. It was thus with the Schoolmen, 
 who subsisted for many centuries on the philosophy of 
 Aristotle; and the science of Cambridge, in 1845, was 
 based on the work of Newton, nearly a century and a half 
 old. Indeed, the spirit was that of Timseus, in Plato's 
 dialogue, who said : ' If we wish to acquire any real 
 acquaintance with astronomy, we shall let the heavenly 
 bodies alone/ In fact, Bacon's advice to proceed by way 
 of experiment and induction had been forgotten. Needless 
 to say, this reproach has long been removed, by the labours 
 of Clerk-Maxwell, Rayleigh, Stokes, and J. J. Thomson. 
 In the 'forties Paris was the home of Fourier, Fresnel, 
 Ampere, Arago, Biot, and Regnault, all physicists and 
 mathematicians of the highest rank ; and Thomson spent 
 a year working in Regnault's laboratory, where experiments 
 on water and steam, their densities, pressure, and specific 
 heats, were being carried on with the utmost refinement. 
 During the next year, 1846, the Chair of Natural Philosophy 
 in Glasgow fell vacant, and, to their credit, the Senate of 
 the day advised Queen Victoria to appoint William 
 Thomson, then a youth of twenty- two, as professor. 
 Never was a choice better justified in its results. For 
 Thomson, by example and by precept, trained many 
 students to be a credit to their old university, and carried 
 out in cellars, which served as laboratories, and which 
 were situated almost next door to that in which James 
 Watt invented the condensing engine, almost all his 
 numerous and important investigations. 
 
 Thomson was not what would be called a good lecturer ; 
 he was too discursive. I doubt whether any man with a 
 
LORD KELVIN 93 
 
 brain so much above the ordinary, so much more rapid in 
 action than the average, can be a first-rate teacher. 
 Certainly, in my own case, I gained much more in my 
 second than in my first year's attendance. But Thomson 
 never allowed the interest of his students to flag ; his 
 aptness in illustration and his vigour of language prevented 
 that. Lecturing one day on ' Couples,' he explained how 
 forces must be applied to constitute a couple, and illus- 
 trated the direction of the forces by turning round the 
 gas-bracket. This led to a discussion on the miserable 
 quality of Glasgow coal-gas, and how it might be improved. 
 Following again the main idea, he caught hold of the 
 door, and swung it to and fro ; but, again, his mind 
 diverged to the difference in the structure of English and 
 Scottish doors. We never forgot what a couple was ; but 
 the idea might have been conveyed more succinctly. 
 He held strong views on the 'absurd, ridiculous, time- 
 wasting, soul-destroying system of British weights and 
 measures ' ; and in spite of all the efforts of the ' Decimal 
 Association,' we, the Americans, and the Russians remain 
 examples of irrational conservatism in respect of the 
 awkwardness of our systems. 
 
 The Cartesian method of locating a point was indelibly 
 impressed on my memory by the following incident: A 
 student, whose position was roughly about the centre of 
 the lecture-room, made that noise so disturbing to a 
 lecturer, yet so difficult to locate, caused by gently rubbing 
 the sole of his foot on the floor. ' Mr. Macfarlane ! ' said 
 Sir William. Mr. Macfarlane, the fides Achates, came, 
 received a whispered communication, and went out of the 
 room. In about ten minutes he returned with a tape-line, 
 and proceeded to measure a length along one wall, on 
 which he made a pencil-mark. He then measured out at 
 right angles another length, and made a chalk-mark on 
 the floor, erecting on it a pointer. ' Mr. Smith, it was you 
 
94 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 who made that noise : be so good as to leave the room/ 
 said Sir William. Mr. Smith blushed and retired. Then 
 came the explanation. Mr. Macfarlane had gone below 
 the sloping tier of seats; had accurately diagnosed the 
 precise position of Mr. Smith's erring foot, and had 
 accurately measured the distance from the two walls. 
 These measurements were reproduced in full view of the 
 students, and the advantages of the system of Cartesian 
 co-ordinates were experimentally demonstrated, while 
 justice was satisfied. 
 
 Owing to an accident, Sir William was lame ; but it did 
 not interfere with his activity of body. Indeed, it lent 
 emphasis to his amusing class demonstration of ' uniform 
 velocity,' when he inarched backwards and forwards 
 behind his lecture-bench, with as even a movement as his 
 lameness would permit ; and the class generally burst into 
 enthusiastic applause when he altered his pace, and intro- 
 duced us to the meaning of the word ' acceleration.' 
 
 In his laboratory Sir William was a most stimulating 
 teacher, though his methods were not those which have 
 since been introduced into physical laboratories. I re- 
 member that my first exercise, which occupied over a 
 week, was to take the kinks out of a bundle of copper 
 wire. Having achieved this with some success, I was 
 placed opposite a quadrant electrometer and made to 
 study its construction and use. I was made to determine 
 the potential difference between all kinds of materials, 
 charged and uncharged ; and among others between the 
 external and internal coatings of a child's balloon, black- 
 leaded externally and internally, and filled with hydrogen. 
 Nor was the Professor always prescient. On one occasion 
 I turned the handle of a large electrical machine, while 
 he held a two-gallon Leiden jar by its knob, and charged 
 the outside coating. It was not until it was fully charged 
 that it occurred to one of us that while the jar was quite 
 
LORD KELVIN 95 
 
 safe as long as it was in his hands, it was impossible for 
 him to deposit it on the table without running the risk of 
 an inconveniently heavy shock. Finally, after rapid de- 
 liberation, two of us held a towel by its corners, and Sir 
 William dropped the jar safely into the middle ; it was 
 then possible to touch the outside without mishap. In 
 short we had little systematic teaching, but were at once 
 launched into knowledge that there is an unknown region 
 where much is to be discovered ; and we were made to 
 feel that we too might help to fathom its depths. 
 Although this method is not without its disadvantages 
 for systematic instruction is of much value there is much 
 to be said for it. On the one hand, too long a course of 
 experimenting on old and well-known lines, as is now 
 the practice among teachers of science, is likely to imbue 
 the young student with the idea that all physics consists 
 in learning the use of apparatus, and in repeating 
 measurements which have already been made. On the 
 other hand, too early attempts to investigate the unknown 
 are likely to prove fruitless for want of manipulative skill, 
 and for want of knowledge of what has already been 
 done. The best of all possible training, however, is to 
 serve as hands for a fertile brain the brain of one who 
 knows what he wishes to discover, who is familiar with all 
 that has already been attempted, and who gradually trains 
 his assistant to take part in the thinking as well as in the 
 manipulation. If at the same time the student is made 
 to read, not merely concerning the problem on which he 
 is immediately engaged, but on all branches of his sub- 
 ject, nothing can be better than such stimulating inter- 
 course with an inventive teacher for those who have ability 
 to profit by it. 
 
 It is extremely difficult to explain Lord Kelvin's contri- 
 butions to knowledge to those who have not themselves 
 some acquaintance with its problems. Let me begin by a 
 
96 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 quotation from Helmholtz, late Professor of Physics in 
 Berlin, an old and intimate friend of Lord Kelvin : 
 ' His peculiar merit consists in his method of treating 
 problems of mathematical physics. He has striven with 
 great consistency to purify the mathematical theory from 
 hypothetical assumptions, which were not a pure expres- 
 sion of the facts. In this way he has done very much to 
 destroy the old unnatural separation between experimental 
 and mathematical physics, and to reduce the latter to a 
 precise and pure expression of the laws of the phenomena. 
 He is an eminent mathematician, but the gift to translate 
 real facts into mathematical equations, and vice versa, is 
 by far more rare than that to find a solution of a given 
 mathematical problem, and in this direction Sir William 
 Thomson is most eminent and original.' When Lord 
 Kelvin began his work, the equivalence of heat and 
 energy was unrecognised; forces were distinguished as 
 ' conservative ' and ' unconservative ' ; the world was sup- 
 posed to be filled with subtle fluids and effluvia ; and it 
 must have seemed almost hopeless to seek any general 
 explanation of material phenomena. Light, heat, elec- 
 tricity, magnetism, and chemical action were all regarded 
 as distinct 'forces,' each a cause of change. Thomson, 
 and his collaborator Tait, the late Professor of Physics in 
 Edinburgh, in their Treatise on Natural PhilosopJty, did 
 much to emphasise the view that Physics deals with 
 things, not theories ; with relations, not with their mathe- 
 matical expression, equations ; and they tried successfully 
 to free the science from the bonds of formal mathematics. 
 They demonstrated that the principle of ' Least Action ' 
 is universal ; that by its help it is possible to explain the 
 motions of the planets and their satellites, of wheels, 
 lathes, machines of all kinds, of every system of which 
 we can define the moving parts and the forces which act 
 on them. 
 
LORD KELVIN 97 
 
 In 1893 Lord Kelvin gave a discourse on 'Isoperi- 
 metric Problems ' at the Royal Institution, in which he 
 attempted to describe the nature of this general problem ; 
 it is that technically called ' Determining a' minimum ' ; 
 and he began with the task which faced Dido of old to 
 surround the most valuable piece of land with a cowhide, 
 i.e. to draw the shortest possible line around it. A 
 similar problem is, to build a railway-line through 
 undulating country at the smallest possible cost ; and one 
 very different in appearance, but related to those already 
 cited, owing to Lord Kelvin's consummate power of dis- 
 covering analogies between phenomena apparently uncon- 
 nected, is the condition of stability of water rotating in 
 an ellipsoidal vessel, and a number of similar problems. 
 Kelvin's work on Elasticity is no less far-reaching ; in 
 Karl Pearson's great treatise on that subject, no less 
 than one hundred pages are filled with Kelvin's con- 
 tributions. 
 
 Lord Kelvin was also the author of a theory of the 
 nature of the ultimate particles of matter the atoms, 
 lie imagined them to consist of 'vortex rings in the 
 ether,' the ether being conceived as a frictionless fluid, all- 
 present, even filling the interstices between the atoms, or 
 ultimate particles of matter. Yortex rings in air, some- 
 times made by smokers, are elastic ; they cannot be cut 
 without being destroyed ; and, in a frictionless fluid, their 
 rotatory motion would be eternal, if once impressed. 
 Recent discoveries may lead to the modification of this 
 theory of the nature of matter ; but it has much in its 
 favour. 
 
 Kelvin was a strong partisan of Joule's work on the 
 equivalence of heat and work. It was believed up to 
 1850 that the heat developed on compressing a gas was 
 ' caloric,' squeezed out of the gas, as one might squeeze 
 water out of a sponge ; but Kelvin taught that heat must 
 
 G 
 
98 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 be due to the motions of the molecules of a gas; and 
 that when the gas is compressed, the impacts of its mole- 
 cules on the walls of the containing vessel are more 
 numerous, and that the work done in compressing a gas 
 appears as heat, owing to the more numerous impacts of 
 its molecules. Following on this, it was necessary to 
 Revise an absolute scale of temperature, and that we also 
 owe to Lord Kelvin. It is based on what is known as the 
 ' Second Law of Thermodynamics ' that heat cannot be 
 transferred from a cold to a hot body without expending 
 work. Following these ideas, Lord Kelvin was led to 
 consider the probable age of the earth, based on an 
 estimate of its original temperature, and the rate at which 
 heat would be lost by radiation. His opinion is that the 
 earth may have been habitable twenty million years ago, 
 but could not have been habitable as long ago as four 
 hundred million years. 
 
 The province of electro-magnetism owes very much to 
 Lord Kelvin. It was he who developed the medium sug- 
 gested by Faraday into a means of representing electro- 
 magnetic forces by analogy with the distortion of an elastic 
 solid. After he had worked out in this manner the con- 
 nection between energy and electro-magnetism, he devised 
 our present system of electrical units volts, amperes, 
 farads, coulombs, etc., and invented machines to deter- 
 mine their numerical values. If it be permitted to assign 
 their relative importance to his contributions to practical 
 science, this must be pronounced the greatest. Without 
 it the science of electricity would be helpless as commerce 
 without a monetary system, and without weights and 
 measures. His work is the foundation of wireless tele- 
 graphy, and of many applications of the electric current. 
 It was he who taught the world how to transmit rapid 
 and trustworthy signals through cables; and he was a 
 pioneer of cable telegraphy. In the old days of cables 
 
LOKD KELVIN 99 
 
 attempts were made to ensure rapid signalling by heavy 
 currents; but Kelvin showed that feeble currents, com- 
 bined with delicate instruments, made the difficulty dis- 
 appear. His 'siphon recorder' is still used, and cannot 
 well be improved on. A great social and commercial 
 revolution dates from August 1858, when the message 
 was signalled under the ocean, ' Europe and America are 
 united by telegraphic communication. " Glory to God in 
 the highest, and on earth peace, goodwill toward men." ' 
 This revolution owed much to Sir William Thomson, who 
 never lost heart and never faltered in the belief that all 
 difficulties would be overcome. His presence on board 
 ship during the laying of the first Atlantic cable directed 
 his attention towards nautical matters ; and to him we 
 owe a deep-sea sounding apparatus, and a compass easily 
 corrected for the magnetic deviations produced by tlie 
 iron or steel used in the construction of ships. 
 
 We must not estimate Lord Kelvin's greatness, how- 
 ever, merely by his own discoveries and inventions, great 
 as these are ; he has served as a model for many disciples. 
 His sincere and single-minded devotion to truth; his 
 interest in the work of others, and his sympathy with 
 their efforts; his fairness of mind and absence of pre- 
 judice ; and his straightforward and loving character have 
 raised the ideals of the whole scientific world, and have 
 deeply influenced the best minds in all countries. His 
 idea of <a treasure of which no words can adequately 
 describe the value ' is : ' Goodwill, kindness, friendship, 
 sympathy, encouragement for more work.' It is to such 
 a man that the world owes an eternal debt of gratitude, 
 and he it was for whom no honour that men have it in their 
 power to bestow could be too great. It is pleasant to be 
 able to state that Lord Kelvin's mental energy was unim- 
 paired by his burden of more than eighty years. He was 
 present at the meeting of the British Association at 
 
100 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Leicester in August 1907, and took part in the discussions 
 on the ' Nature of the Atom.' The minds of most men, 
 like their bodies, grow stiff with age and unreceptive of 
 new impressions ; but Lord Kelvin's until his latest days 
 had all the vigour and elasticity of a young man's. We 
 may well rejoice that he was spared so long to enrich the 
 world with his wisdom and his inimitable example. 
 
PIERRE EUGENE MARCELLIN BERTHELOT 
 
 1827-1907 l 
 
 MARCELLIN BERTHELOT was a native of Paris, born on 
 October 25, 1827, in a flat looking on to the Rue du 
 Mouton, situated in the Place de Greve, now, owing to the 
 activity of Baron Haussmann, the Place de l'H6tel-de- 
 Ville. His father, a doctor of medicine, was a member of 
 the sect of the Jansenists, a small branch of the Gallic 
 Catholic Church. He was a serious man, impatient with 
 the folly of his concitoyens, and somewhat depressed by 
 the poverty and sufferings of his patients. The ' Church 
 of Faith ' had its own Liturgy, and the congregation joined 
 in singing psalms and hymns. Many of the prdtres 
 were among Dr. Berthelot's patients, and young Berthelot 
 must often have listened to discussions on the attempts, 
 ultimately successful, to substitute the Roman for the 
 Gallic liturgy. Dr. Berthelot was married in 1826, shortly 
 after starting practice. His wife was a lively, bright 
 woman, who transmitted her features to her son. 
 
 At that time, Charles the Tenth was on the throne. 
 The allied powers had involved France in a Gouverne- 
 ment de Cures ; and it was part of the State Ceremonial 
 to form a procession, which was headed by the Holy 
 Sacrament and the Papal Nuncio, a cardinal in red, from 
 the Tuileries, to Notre Dame and back, and in which the 
 King, the Queen, the Dauphin (who, according to Madame 
 
 1 A notice which appeared in the Proceedings of the Royal Society for 
 1907. 
 
 101 
 
102 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Berthelot mere, was able to look behind him without turn- 
 ing his head), and the Court took part. The spectators, 
 under the penalty of sacrilege, were obliged to kneel as 
 the Corpus Christi procession passed. Those who refused 
 were prosecuted and severely punished. 
 
 Such a travesty of religion was not to Dr. Berthelot's 
 taste ; the bourgeoisie was liberal and imbued with the 
 sentiments of Voltaire; and the Berthelot family was of 
 the bourgeois class. During the revolutions of 1830 and 
 1848, their house commanded a full view of one of the 
 chief scenes of operation, and young Berthelot must have 
 often been a spectator of many a scene of disturbance and 
 violence. Highly developed intellectually, and mentally 
 impressionable, his later convictions were doubtless largely 
 owing to his early surroundings. 
 
 That Marcellin resembled his mother in features has 
 already been mentioned. But the resemblance was not 
 merely external; there existed between them the most 
 intimate sympathy. Their favourite promenade was in 
 the Bishop's garden behind Notre Dame, along the Quays 
 with their stalls of flowers, and in the Jardin des Plantes. 
 Their minds were both quick and versatile; they were 
 eagerly interested in all that passed around them, and, as 
 Madame Berthelot used to say (borrowing the simile from 
 one of the invasions which she witnessed), they could both 
 ' drive a Russian team with a sure hand and at a full 
 gallop.' The writer, who knew Berthelot only during his 
 later years since 1878 never conversed with any one 
 who possessed such rapidity of thought. Given an idea, 
 with his quick discursive mind he would follow out all 
 possible paths and by-ways, seeing the consequences of 
 this assumption and of that, interposing occasionally a 
 quaint remark, not exactly humorous, but de plaisanterie. 
 He was a delightful conversationalist, interested and in- 
 tensely interesting, willing to discuss all possible subjects, 
 
PIERRE EUGENE MARCELLIN BERTHELOT 103 
 
 and willing, too, to hear all varieties of view, even those 
 contrary to his own opinion. 
 
 His persistence, energy of character, and devotion to 
 duty were inherited from his father. Berthelot used to 
 regret that he had not inherited his mother's optimism. 
 He used to say that when a misfortune overtook her, she 
 had what the French call a crise de larmes, soon over 
 and followed by her usual optimistic cheerfulness ; that a 
 rainbow generally rose through her tears, and that she 
 became gaily resigned to the incurable evil. 
 
 After the demolition of the Rue du Mouton, the family 
 moved to Neuilly, then quite in the country. Renan often 
 looked in on Sundays as a guest at their midday meal. 
 In one of his private letters he tells how Berthelot and 
 he became friends. He had just renounced his clerical 
 orders, and was maUre-repetiteur in a school, where he 
 led a lonely and melancholy existence, depressed by the 
 mental struggles which he had come through, and far 
 from his family and his native Brittany. One day, a 
 pupil about four years younger than himself accosted 
 him; the talk became intimate, and a friendship with 
 Berthelot was soon formed, destined to endure for life. 
 Their intercourse was frequent ; begun early, when both 
 were slender youths, never a year, hardly a month, passed 
 without their seeing each other. Renan used sometimes 
 to poke fun at Berthelot; the tale is told that, passing a 
 cemetery, Renan said to him : ' La, voici la seule place que 
 tu n'as jamais convoitee.' Such sallies were always received 
 with amusement and good temper. On another occasion, 
 provoked by the remark that his coat was worn with the 
 air of a cassock, Renan retorted : ' What is there in you, 
 Marcellin, that gives you the air of just having left off 
 fighting behind a barricade ? ' While Berthelot retained 
 his slender form, Renan became very corpulent ; Berthelot, 
 nervous and active, maintained to the last his almost 
 
104 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 feverish love of work; Renan was meditative almost a 
 dreamer. It was Berthelot's sad duty to speak of his 
 lost friend when the monument at Treguier was raised to 
 his memory. He emphasised Renan's lucidity even to 
 the end, his power of work, his great mental activity ; the 
 words were applicable with equal force to himself. 
 
 Never was there a more devoted couple than Monsieur 
 and Madame Berthelot. After he had ended his brilliant 
 career at the Lycee Henri iv., Berthelot gained the prize 
 of honour at the open competition in 1846. Without any 
 coaching, he passed successively all his degrees Bachelier, 
 Licencie, and Docteur-es-Sciences ; for the doctorate he 
 presented a somewhat sensational thesis, entitled, ' The 
 Compounds of Glycerine with Acids, and the Artificial 
 Production of the Natural Fats.' While working at this 
 research, he was lecture-assistant (preparateur) to Balard, 
 at the College de France. In 1861, largely through the 
 influence of Duruy, then Minister of Public Instruction, 
 Berthelot was promoted to the Chair of Organic Chemistry 
 in that institution; and there he remained all his life. 
 In that year he was awarded by the Academy of Sciences 
 the Jecker Prize for his remarkable researches on the 
 artificial production of organic compounds by synthesis, 
 and at the same time the Academy recommended the 
 creation of the special chair which Berthelot filled so long 
 and so illustriously. In his own words: 'Adonne, des 
 mes debuts dans la vie, au culte de la verite pure, je ne 
 me suis jamais mele a la lutte des interets pratiques qui 
 divisent les hommes. J'ai vecu dans mon laboratoire 
 solitaire, entoure de quelques eleves, mes amis.' 
 
 When he won the Jecker Prize, he was in his thirty- 
 fifth year. The appointment to the Chair at the College 
 de France made it possible for him to marry Mademoiselle 
 Breguet, the daughter of a French Swiss, whose family 
 had made money by manufacturing watches, famed since 
 
PIERRE EUGENE MARCELLIN BERTHELOT 105 
 
 the middle of last century. Monsieur Breguet was a 
 constructeur industriel, or builder of factories. He lived 
 near the Place de I'Hotel-de-Ville, on the Quai de 
 1'Horloge, and the families were acquainted from early 
 days. Mademoiselle was a desirable partie, well-dowered, 
 and of great beauty, which she retained up to the end of 
 her life. She was placid in manner, with lovely eyes, and 
 a brilliant complexion, rendered even more striking, when, 
 at an advanced age, her hair was silver ; and in the church 
 of Saint-Etienne du Mont there is a picture of Sainte- 
 Helene, the lovely face of which is taken from a portrait 
 of Madame Berthelot as a girl. The meeting of the young 
 couple was somewhat romantic : Mademoiselle Breguet, 
 no doubt, must have appeared to Marcellin to be beyond 
 his reach, and besides, his attention was otherwise occupied. 
 But one day, on the Pont Neuf, Mademoiselle was crossing 
 the longest bridge in Paris in the face of a strong wind, 
 wearing a charming Tuscan hat, then the mode. Behind 
 her walked her future husband ; suddenly she turned 
 round, to avoid having her hat blown off, and practically 
 ran into his arms. If not exactly love at first sight, it 
 was a case of love at first touch. Their married life was 
 of the happiest ; indeed, it may be said that they were in 
 love with each other till the end. One of the sons 
 wrote: ' Mon pere et ma mere s'adoraient; jamais le 
 rnoindre nuage n'avait trouble leur bonheur. Us s'etaient 
 compris des le premier jour. Us etaient si bien faits pour 
 se completer ! Bien que tres lettree et fort intelligente, 
 maman s'etait toujours effacee devant son mari, se bornant 
 a s'efforcer de le rendre parfaitement heureux. C'etait, 
 a son avis, la seule fa9on de collaborer a son ceuvre.' 
 Another intimate friend added: 'Monsieur et Madame 
 Berthelot s'adoraient; tous deux etaient de la nature 
 d'elites ; sa compagne n'avait cesse de Fencourager et de 
 le soutenir.' No one visiting their house could fail to 
 
106 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 remark this absolute devotion to each other ; never was 
 there a happier family. Although not a conversationalist, 
 Madame Berthelot, by her perfect tact, her serene manner, 
 and her charming sympathetic face, knew how to make 
 each guest appear at his best; the ball of conversation 
 was lightly tossed round the table, Berthelot himself, by 
 his quaint and paradoxical remarks, contributing his 
 share. A dinner at Berthelot's, in his old house in the 
 Palais Mazarin, the home of the Institute, was a thing to 
 be remembered. Always charitably disposed, Madame 
 Berthelot used to send all the cast-off clothes of the 
 family to the cleaners, and after they had been carefully 
 mended, they were distributed to poor friends. 
 
 In 1881, Berthelot was elected a ' Permanent Senator ' ; 
 he thought it incumbent on him to bear his share in the 
 government of his country. With his wife's help, he 
 managed to carry on his two functions at the same time. 
 In his place in the Senate, Berthelot used to sit buried in 
 his arm-chair, his head thrown back, and his eyes closed, 
 apparently inattentive to all that passed ; but nothing of 
 importance escaped him. He took a leading and active 
 part as member of various Committees dealing with 
 education, and in 1886, as Minister of Education in the 
 Goblet Cabinet, he busied himself with the reform of 
 educational methods in such a manner as to acquire 
 a wide popularity; the Bills introduced by him dealt 
 with primary and with higher instruction, with universi- 
 ties, and with technical schools ; in the last he was no 
 believer, except in so far as manual training was given. 
 Later, in 1895, he was for a short time Foreign Minister 
 in the Bourgeois Cabinet ; but the delays of parliamentary 
 procedure were not to his mind. It was with difficulty 
 that he was persuaded to sign the Anglo-French Treaty 
 denning the position of Siam ; and, almost immediately 
 after, he resigned office. 
 
PIERRE EUGENE MARCELLIN BERTHELOT 107 
 
 Berthelot's career is easily told ; it consisted of honour 
 after honour. He was elected a Member of the Academic 
 de Medecine in 1863, and in 1867 he collaborated in the 
 foundation of the Ecole des Hautes Etudes, and in the 
 reorganisation of scientific teaching. Membership of the 
 Academic des Sciences followed in 1873, and in 1889 he 
 became its Secretaire Perpetuel. 
 
 In 1900, he had the rare honour of being elected among 
 the immortal forty in the Academic Franaise, succeeding 
 to the Chair of Joseph Bertrand. Of 28 voters, 19 voted 
 for him, 9 abstaining. Four years later, in 1904, he 
 delivered the statutory discourse. He was a Member of 
 the Conseil Superieur des Beaux-Arts, of the Conseil 
 Superieur de V Instruction Publique, and in 1886 he was 
 created a Grand Officier of the Legion of Honour. He 
 was Foreign Member of almost every scientific society 
 in the world, including our own Royal Society. 
 
 On November 24, 1901, the Berthelot jubilee celebration, 
 the anniversary of his seventy-fifth birthday, was held in 
 Paris, M. Loubet, President of the Republic, in the chair. 
 It took place in the great hall of the Sorbonne ; all the 
 Cabinet, the ambassadors of all countries, and delegates 
 from universities and scientific societies from all over the 
 world were present. Madame Berthelot with her children 
 and grandchildren occupied a conspicuous place, beaming 
 over with unaffected pleasure ; Berthelot had declined the 
 State offer to make a triumphal procession in the carriage 
 of the President with a military escort ; he went on foot 
 from the Quai Voltaire to the Sorbonne, his greatcoat 
 buttoned so as to hide the grand-cordon of the Legion 
 of Honour, and his head down so as to avoid recognition. 
 He was embraced by the President of the Republic, and 
 amid the enthusiastic applause of the spectators, address 
 after address was delivered, each delegate conveying the 
 congratulations of the body which he represented. It 
 
108 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 was a national fete. Thus did the French honour science 
 and its doyen. 
 
 On March 18, 1907, the end came. Madame Berthelot 
 had been ailing for about three months ; it turned out to 
 be an attack of heart-disease, dangerous at the age of 
 seventy. After she was confined to bed, Berthelot watched 
 by her each night, seated in a deep arm-chair, only leaving 
 her when she was asleep. He himself suffered from the 
 same disease, and it was accelerated by his want of rest. 
 His family noticed his feverish appearance in the morn- 
 ings ; he excused himself by saying that he was finishing 
 a memoir for publication. On Passion Sunday there was 
 a slight improvement, and Berthelot passed the afternoon 
 in his laboratory at Meudon. That night, however, 
 Madame Berthelot became comatose, and her husband 
 never left her bedside until Monday at four, when the end 
 came. Berthelot suddenly rose from the arm-chair in 
 which he was seated, threw his arms in the air, uttered a 
 cry, and fell back dead. They died, as they had lived, 
 together. 
 
 It now remains to give a sketch of Berthelot's scientific 
 work. The ' Prix- Jecker ' has already been alluded to. 
 This was the reward of his labours on the synthesis of 
 carbon compounds. He began in 1851 by investigating 
 the action of a red-heat on alcohol, acetic acid, naphtha- 
 lene, and benzene ; this led him in 1860 to the rediscovery 
 of acetylene, a compound originally obtained by Edmund 
 Davy, Sir Humphry's brother. In 1856 he synthesised 
 methane by the action of a mixture of sulphuretted 
 hydrogen with carbon disulphide on copper ; and in 1862 
 he obtained ethylene and acetylene by heating marsh-gas 
 to redness. His condensation of acetylene to benzene in 
 1866 established the first link between the fatty and the 
 aromatic series. His direct synthesis of acetylene from 
 carbon and hydrogen in 1862, and the formation of alcohol 
 
PIERRE EUGJBNE MARCELLIN BERTHELOT 109 
 
 by hydrolysing ethyl- sulphuric acid, obtained by absorbing 
 ethylene in sulphuric acid, taken in conjunction with his 
 synthesis of hydrocyanic acid in 1868, pointed the way to 
 the formation from the elements of innumerable com- 
 plicated compounds of carbon. 
 
 Much light has also been thrown by Berthelot on the 
 alcohols. In 1857 he produced methyl alcohol from 
 marsh-gas by chlorination and hydrolysis; in 1858 he 
 recognised eholesterine, trehalose, meconine, and camphol 
 as alcohols ; in 1863 he added thymol, phenol, and cresol 
 to the same class ; and he showed how to diagnose alcohols 
 by acetylation. 
 
 Turning to the esters, the nature of glycerine occupied 
 his attention in 1853 ; in that year he succeeded in syn- 
 thesising some animal fats, and showing their analogy 
 with esters, as has already been mentioned ; and he pre- 
 pared other salts of glyceryl by submitting it to the action 
 of acids. The action of hydriodic acid was, however, 
 found to yield two substances of a different nature, namely 
 isopropyl iodide, and allyl iodide ; and from the latter he 
 prepared, for the first time, artificial oil of mustard. The 
 analogy of sugars with glycerine led him to investigate 
 the action of acids on sugars, and this resulted in the 
 synthesis of many of their esters. The fermentation of 
 mannite and other polyhydric alcohols was also studied 
 in 1856 and 1857, also the conversion of mannite and 
 glycerine into sugars, properly so called. The esters of 
 pinite, etc., with tartaric acid, were also studied, and in 
 1858, trehalose and melezitose were discovered. In 1859, 
 Berthelot maintained that the action of yeast is not a vital, 
 but a chemical phenomenon ; and he returned again and 
 again to the study of fermentation. 
 
 These and other similar investigations on esters led him, 
 in conjunction with Pean de Saint- Gilles, to investigate 
 the rate of esterification ; and the experiments, begun in 
 
110 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 1861, led to a long piece of work on chemical equilibrium, 
 and on 'affinity.' In 1869 he attempted to limit the 
 action of hydrochloric acid on zinc by pressure, but unsuc- 
 cessfully ; and in the same year he investigated the 
 equilibrium between carbon and hydrogen, in sparking 
 acetylene under pressure. And later in that year he 
 announced laws, describing the partition of bodies between 
 two solvents, and he investigated the state of equilibrium 
 in solution. In the same year appeared the first of the 
 long series of researches on thermal chemistry. In 18*75 
 he returned to the subject of chemical equilibrium, deal- 
 ing with the partition of acids between several bases in 
 solution. 
 
 Among other syntheses was that of formic acid from 
 caustic soda and carbon monoxide ; oxalic acid was pro- 
 duced by the oxidation of acetylene ; and acetates, by the 
 slow oxidation of acetylene, in contact with air and 
 caustic potash, in diffuse daylight. 
 
 In 1857 the combination of unsaturated hydrocarbons 
 with the halogen acids was studied, as well as the conver- 
 sion of chloro- and bromo-hydrocarbons into hydrocarbons 
 by reduction. In 1860 ethyl iodide was synthesised by 
 the union of ethylene with hydriodic acid; and in 1867 
 the use of a concentrated solution of hydriodic acid as a 
 universal reducing agent at high temperatures was dis- 
 covered. 
 
 Berth elot's numerous and important researches on the 
 acetylides of silver and copper doubtless led him to pay 
 attention to explosives. Begun in 1862, they were con- 
 tinued until 1866 ; and in that year he enunciated the 
 theory that the production of mineral oils may conceivably 
 have been due to the action of water and carbonic acid on 
 acetylides of the alkaline metals, and to the subsequent 
 resolutions of acetylene at a high temperature into other 
 hydrocarbons. These researches on the acetylides were 
 
PIERRE EUGENE MARCELLIN BERTHELOT 111 
 
 followed in 1870 by investigations on the explosive force 
 of powders, the explosions being carried out in a calori- 
 meter. 
 
 In 1871 Berthelot proceeded to investigate the detona- 
 tion of mixtures of gases, and he made measurements of 
 the heat of formation of nitro-glycerine. In 1874 and 
 1876 the work was continued ; and in 1877 it was extended 
 to the temperatures of explosive mixtures, and to the 
 velocity of combustion. In 1878 explosive mixtures of 
 dust with air, and in 1880 fulminating mercury, were 
 examined. A research on the velocity of the explosive 
 wave in gases followed in 1882 ; and in 1884 measure- 
 ments of the specific heats of gases at high temperatures 
 were made. In the same year the calorimetric bomb was 
 invented ; and in 1892 it was adapted to the requirements 
 of organic analysis. 
 
 Allotropic varieties of the elements also claimed Ber- 
 thelot's attention. In 1857 he commenced with a study 
 of allotropic varieties of sulphur ; and in 1870 he investi- 
 gated these varieties thermally. In 1869 he examined 
 the allotropic varieties of carbon, and this led him to the 
 preparation of various forms of graphitic oxides. Allo- 
 tropic silver and other allotropic forms were also the 
 subject of his research. 
 
 Berthelot also did much work by help of the 'silent 
 discharge.' Attracted to it in 1876, when he submitted 
 mixtures of organic substances with nitrogen to its 
 influence, and succeeded in causing the nitrogen to enter 
 into combination, he repeated Brodie's experiments, and 
 reproduced the oxide C 4 4 . In 1878 he produced by the 
 same means the higher oxide of sulphur, S 2 7 , in needles 
 often a centimetre in length, and in 1881 pernitric 
 anhydride. In 1895 he carried out similar work with 
 argon, and later with helium. 
 
 From an early date Berthelot interested himself in 
 
112 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 agricultural chemistry. From his laboratory at Meudon, 
 assisted by his colleague, Andre, have appeared a succes- 
 sion of memoirs, chiefly relating to the absorption of 
 nitrogen by plants, and to their behaviour under the 
 influence of electric energy. To the very end his interest 
 was kept up in these experiments ; and he was hopeful of 
 increasing by electrical means the productiveness of 
 cereals, and of adding to the world's food-supply. 
 
 Though so keenly alive to the present, the past had for 
 Berthelot a great attraction. In 1877 he analysed a 
 sample of Roman wine, which had been preserved in a 
 sealed flask ; and he has contributed to the Journals many 
 notices of the composition of ancient objects of metal. 
 His works on Les Origines de VAlchimie, and on a Collec- 
 tion des anciens Alchimistes grecs, texte et traduction, and 
 his Introduction d I' etude de la Chimie des Anciens et du 
 moyen dge,' involved long research of ancient manuscripts ; 
 he acquired facility in reading ancient Greek, though for 
 Arabian sources he was dependent on others. 
 
 Berthelot was the author of numerous works besides 
 those on Alchemy. In 1872 he published a Treatise on 
 Organic Chemistry; a fourth edition appeared in 1899. 
 This was followed by La Synthese chimique ; Essai de 
 Chimie mechanique (1879), in which he announced the 
 principle of ' maximum work,' a doctrine afterwards with- 
 drawn, or, at least, greatly modified in 1894; Traite 
 2^ratique de Calorimetrie chimique (1893); Thermochimie : 
 Donnees et lois numeriques (1898), in which an account 
 of his long series of calorimetrical measurements is 
 given ; this work and that of Julius Thomsen on Ther- 
 .mochimie are the standard books on the subject, and 
 each contains the results of the individual researches of 
 its author. 
 
 Berthelot's mind was one which interested itself greatly, 
 not merely with things, but with their origins; and in 
 
PIERRE EUGfeNE MARCELLIN BERTHELOT 113 
 
 Science et Philosopliie and Science et Morale he treats of 
 the relation of science to human thought. The same 
 critical spirit manifests itself in his Histoire des Sciences : 
 La Chimie au moyen age, in which Syrian and Arabian 
 Alchemy is treated of. 
 
 A partisan of Lavoisier, La Revolution chimique de 
 Lavoisier presents that point of view strongly. He also 
 published in 1898 his correspondence with Renan. 
 
 The lectures which he delivered at the College de 
 France were published under the titles Lecons sur les 
 Methodes generates de Synthese en Chimie organique ; 
 Lemons sur la thermochimie ; Lecons sur les principes 
 sucres ; and Lecons sur I'isomerie. The application of 
 thermal chemistry to problems of life was treated of in 
 his Chaleur animate, and in 1901 he published three 
 volumes on Les Carbures d'Hydrogene. 
 
 One point remains to be mentioned. It has sometimes 
 been objected that Berthelot kept science on a wrong 
 path by persistently retaining the old system of represent- 
 ing formulae, after all the rest of the world had aban- 
 doned it. The writer remembers well a conversation in 
 the late '80's, in which Berthelot defended his views. He 
 thought the position of those who employed the customary 
 notation (and, of course, they comprised practically the 
 whole chemical world) not unlike that of the defenders of 
 the phlogiston theory ! The retort was obvious, but not 
 made. Berthelot had not even the excuse of Cavendish, 
 who, after a calm, deliberate statement of the results of 
 his research in terms of the then new hypothesis of 
 Lavoisier, restated it in terms of the phlogistic method, 
 saying that he preferred to make use of the older and 
 better known language, rather than of the newer modes 
 of expression. For in 1890 Berthelot was, perhaps, the 
 only survivor of the older chemists. Professor Guye, who 
 attended his lectures in 1890-91, tells that the session was 
 
 H 
 
114 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 begun, as usual, with the special notation of which Ber- 
 thelot was the sole defender (' equivalents based on two 
 volumes of vapour '), and that, without the slightest warn- 
 ing in the middle of a chapitre, to the great astonishment of 
 his audience, he effected the change, dealing with a subject 
 of which the first portion had been expounded in the 
 ' equivalent ' notation, and continuing in the newer nota- 
 tion of which he had so long been the opponent. 
 
 No one is more conscious than the writer that he has 
 failed to do justice to this remarkable personality. His 
 only excuse is that he has done his best. He wishes that 
 it were possible to convey to the reader a sense of the 
 brilliancy, the vivacity, the power, the ability, the talent, 
 and the high character of the great chemist. In the life- 
 like plaquette by Chaplain, his features and his attitude 
 have been admirably reproduced. Truly he was one of 
 the most remarkable of the eminent men of whom France 
 may be proud. He and his wife lie in the vaults of the 
 Pantheon, in life united, in death not put asunder. 
 
II. CHEMICAL ESSAYS 
 
 HOW DISCOVERIES ARE MADE 
 
 THERE is a difference between discovery and invention. 
 A discovery brings to light what existed before, but what 
 was not known ; an invention is the contrivance of some- 
 thing that did not exist before. I suppose, however, that 
 inventions and discoveries are made in much the same 
 manner ; though I have no claim to speak as an inventor, 
 except in a very small way. 
 
 Many people, probably most people, think that when a 
 discovery is made, it comes all in a flash, as it were that 
 a new idea suddenly crops up, and its conception is a dis- 
 covery. That may sometimes be the case. 
 
 We have all heard of the puzzle given to Archimedes ; 
 how he was asked to find out, without injuring it in the 
 least, whether a certain crown consisted of silver or of 
 gold ; and by weighing it in air and in water, he invented 
 the method of taking specific gravity; for the crown when 
 weighed in water lost weight equal to that of the water 
 which it displaced. And he ran through the streets of 
 Alexandria, crying, ' Heureka ! I have found it ! ' 
 
 His finding that the crown was of gold was a discovery ; 
 but he invented the method of determining the density of 
 solids. Indeed, discoverers must generally be inventors ; 
 though inventors are not necessarily discoverers. 
 
 116 
 
116 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 It is too often supposed that, like the poet, discoverers 
 are ' born, not made ' ; but I think I shall be able to show 
 that many people, though not all, have in them the power 
 of making discoveries ; and if this short article can give 
 to any one the hope of making discoveries, and prompt 
 him to try, it will have more than achieved its object. 
 
 Like every other endeavour, the beginning is in small 
 things. Any one who tries to look into anything with 
 sufficient care will find something new. A drop of water ; 
 a grain of sand ; an insect ; a blade of grass ; we know in- 
 deed little about them when all is told. First, of course, 
 we must learn what others have done ; and for that pur- 
 pose we go to school and to college, and read books and 
 hear lectures. Before beginning, we should at least have 
 an idea of what has been achieved by our predecessors. 
 After that there is nothing for it but to try. 
 
 But there are two ways of trying : and Avhat I wish to 
 convey is best told in an allegory. 
 
 There are two kinds of fishers : those who fish for 
 sprats and those who angle for salmon. I do not say 
 there are not others ; but these two kinds are at the 
 extremes of the fishing world. The fishers for sprats are 
 sure of a large catch, or at least of catching something ; 
 but the fish are small, not particularly attractive as food, 
 and of no great value ; they are, however, numerous and 
 easily caught. But the salmon fisher hunts a very dif- 
 ferent prey ; if there is any special quality about a salmon, 
 it is his power of motion and his fickleness of taste ; so 
 that the angler, when he casts his line, is by no means 
 sure that a fish is within reach of his cast, nor, if he is, 
 whether he will rise to the fly. If fate is propitious, how- 
 ever, his prize is a great one; his pleasure consists not 
 merely in catching the fish, but in struggling with him, 
 possibly for an hour or more ; wading after him in alter- 
 nate hope and fear hope that his line may stand the 
 
HOW DISCOVERIES ARE MADE 117 
 
 strain, fear that it may part, or that some hasty move- 
 ment may lose him his fish. 
 
 Most discoverers are like fishers for sprats : they go 
 where they are sure of a reward ; but the gain is not 
 great, at least as regards sport. It is much more fun to 
 fish for salmon ; but then there is a great chance that the 
 angler has mistaken the place to fish, or that he has used 
 the wrong fly ; or that the weather is unfavourable ; or 
 that a hundred things, impossible to foresee, will prevent 
 the salmon taking the hook. 
 
 We may not pursue the allegory further: salmon are 
 now not nearly so plentiful a$ they used to be; sprats, 
 perhaps even more numerous. And it requires training 
 and a good eye to know where the salmon lie and in what 
 pools to fish. 
 
 But let us dismiss this image and become historical. 
 
 One of the first puzzles which awaited solution was the 
 nature of flame. The ancients believed it to be an ele- 
 ment that is, a property, or perhaps a constituent of 
 most, or of all, other things. Flame, said they, is hot; 
 and everything which is hot partakes of the nature of 
 flame. 
 
 Robert Boyle guessed that it was a sign of the rapid 
 movement of the minute particles of which he supposed 
 everything to be composed ; but this, although very near 
 what we now suppose to be the truth, was merely a lucky 
 guess ; for he had no real ground for making the sugges- 
 tion. It was noticed that flame appears when anything 
 burns; and the reason for combustion, or burning, had 
 first to be sought. 
 
 The real step towards this was made by Joseph Priestley, 
 an English dissenting minister, and by Karl Scheele, a 
 Swedish apothecary, almost at the same time. Priestley 
 was a fisher for salmon, to revert to our old image ; he 
 fished everywhere and caught many large fish. And so 
 
 \ 
 
118 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 was Scheele. They noticed that when certain substances 
 were heated, gases or, as they termed them, 'airs' escape. 
 For it had been supposed that all gases, as we now name 
 them, were merely modifications of ordinary air ; just as 
 we sometimes notice a pleasant or a disagreeable smell, 
 and attribute it to the ' goodness ' or ' badness ' of the air, so 
 it was generally thought that gases, such as coal-gas, were 
 a sort of air with an unpleasant odour and the curious 
 property of catching fire. 
 
 About fifteen years before Priestley and Scheele made 
 their great discovery of oxygen, the constituent of air 
 which supports combustion, a Scottish professor, Joseph 
 Black, investigated the particular kind of 'air' which 
 escapes when chalk or limestone is heated. And he made 
 the great discovery that this ' air ' can be reabsorbed by 
 lime the residue left after chalk is heated so that 
 chalk is again formed. 
 
 Moreover, he weighed the chalk before it was heated, 
 he measured the gas, and he weighed the lime left after 
 the gas had been driven off from the chalk. And lastly 
 he weighed the chalk which was re-formed after the lime 
 had absorbed the gas. 
 
 He found that the lime was lighter by just as much 
 as the gas weighed ; and he called this gas ' fixed air/ to 
 emphasise the fact that it could be ' fixed ' or absorbed by 
 lime and similar substances. 
 
 This first opened the way for the investigation of gases ; 
 it was a great discovery perhaps one of the most fertile 
 which has ever been made. It is to be noted that Black 
 was not content with this, however; for he recognised 
 that the fixed air from chalk was of the same nature as 
 steam from water. And just as it was necessary to heat 
 water so as to drive it into steam, so it appeared to him 
 that carbonic acid gas, to give ' fixed air ' a more modern 
 name, was a gas by virtue of the heat or ' caloric ' which it 
 
HOW DISCOVERIES ARE MADE 119 
 
 contained. He went on to discover how much heat is 
 required to convert a known weight of water into steam. 
 He found that about fifty-four times as much heat is 
 required as is necessary to heat the same weight of water 
 from the freezing-point to the boiling-point. But the 
 steam is no hotter than the boiling water ; hence Black 
 called this heat the ' latent heat ' of steam, because it lies 
 hidden in the steam and does not affect a thermometer. 
 Black made quantitative experiments that is, he not 
 merely made discoveries, but found the quantities in 
 which the changes took place. 
 
 The way was now plain for Priestley and Scheele. They 
 heated all kinds of substances : if they evolved gas, that 
 gas was collected and examined ; but neither Priestley nor 
 Scheele paid much attention to quantities. The methods 
 of dealing with gases had to be invented, moreover. And 
 while Scheele caught his gases in bladders, Priestley in- 
 vented, or rather reinvented, what he called a ' pneumatic 
 trough,' a vessel filled with water containing jars and 
 bottles standing inverted full of water. If the tube lead- 
 ing from the retort in which the substance evolving the 
 gas was heated was directed so that its open end was 
 directly under the mouth of the bottle, the escaping gas 
 entered the bottle and displaced the water ; and when the 
 bottle was full, it could be corked, still under water, and 
 removed so that the gas could be examined. 
 
 It is usually the case that discoveries have to be accom- 
 panied by inventions; the sequence is that to try any 
 new thing, a piece of apparatus has to be devised which 
 will effect the purpose or perhaps an apparatus already 
 known has to be altered so that it may almost be said 
 that invention and discovery go hand in hand. 
 
 For this reason it is very important that the discoverer 
 should be a good worker in all kinds of materials in glass, 
 for most small pieces of apparatus can best be constructed 
 
120 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 of glass : in brass, for if anything of the nature of machinery, 
 such as pumps, stirrers, etc., is required, brass is perhaps 
 the most convenient material; in clay, for vessels are 
 wanted which will withstand a high temperature ; and of 
 recent years silica glass, made from fused rock-crystal, has 
 proved of great use, for it can be worked before a blow-pipe 
 fed with coal-gas and oxygen. 
 
 But to return to the discovery of oxygen. Priestley 
 heated oxide of mercury, or, as he called it, ' red precipi- 
 tate,' in a retort, and collected the escaping gas; and he 
 found that a candle burned in it much more brightly than 
 in air; and, moreover, after having found that a mouse 
 could live in it longer than in the same volume of air, 
 confined in a bottle, he breathed it himself and found 
 that its effect was pleasant and exhilarating. 
 
 Similar experiments were made by Scheele with the 
 same result; but Scheele went much further. Having 
 noticed that a number of substances had the property of 
 making combustible bodies, such as wood, flour, and 
 charcoal, deflagrate, or burn more brilliantly when mixed 
 with them, he heated these substances, and found that 
 they too evolved oxygen gas. Among the substances 
 were red-lead, black oxide of manganese, nitre, and many 
 others ; so he established a general rule that those sub- 
 stances which can be mixed with charcoal to make a kind 
 of gunpowder will evolve oxygen when heated. 
 
 It thus became known that air contained a gas, amount- 
 ing to about a fifth Scheele says a sixth of its bulk, 
 possessing the property of making combustible objects 
 burn with greater vigour. Flame, therefore, was caused 
 by the action of oxygen, as the new gas was called later, 
 with combustible bodies. 
 
 It would take too long to consider the curious doctrine 
 of 'phlogiston,' an immaterial effluvium which was sup- 
 posed to escape when bodies burn ; I can merely mention 
 
HOW DISCOVERIES ARE MADE 121 
 
 that Lavoisier, a celebrated French chemist, gave the 
 correct explanation of combustion namely, that it is 
 caused by the union of oxygen with the substance burning. 
 Lavoisier, however, cannot be ranked as a great discoverer, 
 though he shone as an interpreter of the discoveries of 
 others. 
 
 Henry Cavendish, who did his best work between 1770 
 and 1790, discovered the composition of water ; that it is 
 produced when oxygen and hydrogen unite; and he 
 determined with great accuracy the proportions by volume 
 in which the union of the two gases is completed. He 
 also attempted to show, by passing electric sparks through 
 a mixture of the inert gas of the atmosphere, nitrogen, 
 mixed with oxygen, that nitrogen was a single substance 
 and not a mixture ; nearly all the nitrogen disappeared 
 under this treatment, only about one hundred-and- 
 twenty-fifth of the whole being left. It would hardly 
 have been possible for him, in the existing state of know- 
 ledge, with the imperfect appliances which alone were 
 available at that time, to have identified his inactive 
 residue with 'argon/ a gas discovered more than a 
 century later; for the spectroscope was then unknown, 
 and it is the chief means of identifying and characterising 
 gases, and indeed elements of every kind. This is an 
 example of how discovery has sometimes to wait on in- 
 vention ; for, until the instruments of research are invented, 
 it is almost impossible to confirm a discovery, even 
 although it may be genuine. 
 
 The true nature of flame, which, as before remarked, 
 has been a puzzle since the remotest ages, has had to 
 wait on invention for its discovery. When a current of 
 electricity of high tension, such as is produced by an 
 induction-coil or by an electric machine, is passed through 
 any rarefied gas, it gives out a peculiar and often a very 
 beautiful coloured light : sometimes red, as in the case of 
 
122 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 hydrogen or neon; sometimes bluish-white, as with 
 carbonic acid or krypton ; sometimes purple-red, as with 
 argon or nitrogen. When examined through a prism or 
 a spectroscope, this light is seen to consist of a number of 
 colours, which blend to give the colour seen with the 
 naked eye. 
 
 Thus the brilliantly red spectrum of hydrogen is easily 
 shown to be a compound impression ; the red light, which 
 is the brightest, is mixed with and slightly modified by 
 a blue- green and a violet light. Tubes which are well 
 adapted to show this light were invented by a German 
 physicist named Plticker in the 'fifties. Twenty-five 
 years later, Sir William Crookes, with the aid of his 
 skilful assistant, Mr. Gimingham, improved the then 
 existing form of air-pump, invented by Dr. Hermann 
 Sprengel, so that it became capable of exhausting the 
 air much more completely than was previously pos- 
 sible. 
 
 He found that, at a much greater exhaustion than that 
 which causes gases to glow and give out their spectrum, a 
 current of high-tension electricity produced in the tube a 
 violet or a green phosphorescence, according as the glass 
 of which it was made contained lead and potash, or lime 
 and soda, combined with the silica, or sand. 
 
 Moreover, the position of this curious phosphorescent 
 glow depended on the shape and direction of the wire or 
 plate from which the negative electricity passed into the 
 tube. From a wire the glow proceeded in all directions 
 perpendicular with its length, so as to colour the tubes 
 immediately surrounding the wire with phosphorescent 
 light. If the wire, however, were terminated with a plate, 
 then the phosphorescent light appeared mostly between 
 the front of the plate and the positive wire of the vacuum- 
 tube. Supposing the plate were curved, so as to form a 
 concave metallic reflector, the light of what was evidently 
 
HOW DISCOVERIES ARE MADE 123 
 
 a discharge was concentrated on a point at the focus of 
 the metallic mirror. 
 
 Moreover, if an object of any kind were placed at the 
 focus, and submitted to the discharge, it became intensely 
 hot; or if it could move if, for instance, it formed the 
 vanes of a little wheel or windmill the wheel revolved 
 rapidly as if it were being bombarded by infinitesimally 
 small bullets. Crookes imagined that by being thus 
 highly rarefied, the gaseous matter changed so as to 
 become ' ultra-gaseous,' that it changed its state in some- 
 what the same manner as ice becomes water or as water 
 becomes steam. 
 
 It is interesting here to recall how Sir William Crookes 
 came to make these most remarkable discoveries. He 
 began by using a spectroscope to investigate the spectrum 
 or coloured light given out by the various constituents 
 into which he had analysed the dust which deposits in 
 the flues used to convey the sulphurous acid produced by 
 the burning of pyrites (a compound of sulphur and iron), 
 then (in the 'sixties) recently introduced as a source of 
 sulphur for the manufacture of sulphuric acid or oil of 
 vitriol. One of his precipitates, when examined with the 
 spectroscope, showed the presence of a bright green light ; 
 and this was traced to the presence of a new element, to 
 which he gave the name 'thallium,' from the Greek 
 thallos, a green twig. 
 
 One of the first things done with a new element is to 
 try to discover its ' equivalent' that is, the proportion by 
 weight of the element which will combine with 8 parts 
 by weight of oxygen. (The number 8 is chosen, because 
 8 parts by weight of oxygen combine with 1 part of 
 hydrogen to form water.) The weighings require to be 
 very accurately made; and a peculiarity which affects all 
 attempts to weigh very accurately must now be told of. 
 The question is often asked as a catch : ' Which weighs 
 
124 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 most : a pound of feathers or a pound of lead ? ' The 
 usual answer is, ' They weigh the same.' 
 
 Although this is strictly true (for a pound is a pound, 
 whether of lead or feathers), a little consideration will 
 show that when the feathers are placed on one pan of a 
 pair of scales and the lead on the other, the lead takes up 
 far less room than the feathers; in other words, the 
 feathers displace much air, while the lead displaces little. 
 That is, the air which the feathers displace no longer 
 rests on the pan ; and if it were still there, the feathers 
 would weigh more. Hence a so-called pound of feathers 
 weighs less than it ought to by the weight of the air 
 displaced. 
 
 Now to overcome this difficulty and to avoid the some- 
 what complicated and uncertain calculations necessary to 
 ascertain the true weight of the things weighed, Sir 
 William Crookes devised a balance closed in by a case in 
 which a vacuum could be made. And it was while 
 obtaining this vacuum that he discovered that light 
 apparently (but really heat) appears to repel certain 
 objects more than others. Thus he was led to experi- 
 ment on vacuum-tubes and to perform all the beautiful 
 experiments which have made his name so famous. At 
 the same time he invented the ' radiometer,' a pretty little 
 toy for showing the repelling action of heat. 
 
 Here again we see the advantage of following up small 
 trails; they may widen to great and most important 
 roads. If Sir William had been content to weigh his 
 compounds of thallium in his vacuum-balance, as most 
 others would have done, and had not had the genius to 
 follow this side-track, he would have missed many of his 
 greatest discoveries. 
 
 A further great step was made when the German 
 physicist Lenard found that Crookes's ' rays ' the ' fourth 
 form of matter ' which he supposed to be repelled from 
 
HOW DISCOVERIES ARE MADE 125 
 
 the negative pole of the Plucker tube when very highly 
 exhausted could pass out of the tube through a thin 
 1 window ' of the very light and strong metal aluminium. 
 It is true they could not pass very far ; they soon became 
 scattered. Here was a discovery made with a set purpose. 
 Professor Lenard wished to decide the question whether 
 Crookes's ' rays ' were really due to a stream of corpuscles 
 or whether they were vibrations like those of light. 
 
 Sir William had previously found that if a magnet were 
 placed near the tube the path of the rays was no longer 
 straight, but curved. And Lenard observed that if the 
 aluminium window were placed so that a ' vacuum ' (not 
 a complete, but a nearly complete one) were on both sides of 
 the aluminium window, the 'rays' could be bent out of their 
 course by the magnet after passing through the window. 
 
 It must be remembered that these rays are not them- 
 selves visible ; it is only possible to see where they strike 
 by their causing phosphorescence. Professor Rontgen, 
 the celebrated German physicist, discovered in his turn 
 that if these rays be suddenly stopped say by falling on 
 glass or metal rays of another kind are sent on, which 
 have the power of affecting a photographic plate and of 
 rendering certain substances exposed to them phosphores- 
 cent; so that, as different kinds of matter have very 
 different powers of stopping Rontgen rays, it is possible to 
 photograph the bones of the body, although the flesh is 
 comparatively transparent to them. The bones, as it 
 were, cast their shadow ; or the shadow of the bones can 
 be thrown on a piece of card, painted with material which 
 phosphoresces and shines when exposed to the impact of 
 the rays. 
 
 I believe that Rontgen's discovery arose from an acci- 
 dental observation that a box of photographic plates left 
 near a Crookes's tube became 'fogged/ and he too had 
 genius to follow up this clue. 
 
126 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 We are getting on rather slowly, however, in the hunt 
 for an explanation of flame. A great step in advance was 
 made by the discovery of radium by Madame Curie. 
 
 Radium is a metal, the salts of which continually give 
 out ' Lenard rays/ or ' Crookes's rays.' And it is certain 
 that it is losing substance during their emission. 
 
 Mr. Soddy and I have actually trapped and measured 
 one of the products which is being thrown off by radium 
 while these rays are being shot out; it is a gas called 
 ' radium emanation.' And it in its turn decomposes and is 
 changed to some extent into the gaseous element helium, 
 which I discovered in 1895. 
 
 All the while that these changes are taking place, what 
 are called ' /3-rays ' (beta-rays) are being evolved, and the 
 opinion is now generally held that these so-called rays are 
 really negative electricity, and are identical with the 
 ' cathode-rays ' of Lenard. 
 
 I have been frequently asked : ' But is not electricity a 
 vibration ? How can wireless telegraphy be explained by 
 the passage of little particles or corpuscles ? ' The answer 
 is 'Electricity is a thing', it is these minute corpuscles, 
 but when they leave any object, a wave, like a wave of 
 light, spreads through the ether, and this wave is used for 
 wireless telegraphy.' 
 
 It has been found that flames are capable of conducting 
 electricity, while gases, under the usual atmospheric 
 pressure, are very good insulators, and sparks can pass 
 through air only when the current is one of very high 
 tension. Now, in flames rapid chemical action is taking 
 place; compounds are burning that is, their constituents 
 are in the act of uniting with oxygen. 
 
 Although it is not certain that /3-rays or, to give their 
 other name, corpuscles of electricity are being shot out 
 during such changes, it is not improbable that they are. 
 No doubt they impinge on the neighbouring atoms and 
 
HOW DISCOVERIES ARE MADE 127 
 
 set them in rapid vibration ; and they may even break up 
 molecules and cause them to assume other forms of 
 combination. And in doing so, very short electric waves 
 are sent out through the ether, and these are what we 
 term ' light/ and ' radiant ' heat. 
 
 There are several other lines of evidence which support 
 this notion. For example, a pure gas cannot be heated 
 red-hot or made to glow by heat alone. There must be a 
 chemical change of some kind at the same time. Again, 
 a Welsbach incandescent gas mantle, if made of pure 
 thoria (and that means ' nearly pure,' because we are not 
 acquainted with really pure substances), does not give out 
 much light when heated, but if some other earth, such as 
 oxide of cerium, is mixed with the thoria, the familiar 
 brilliant incandescence is produced when it is heated by a 
 Bunsen burner. The ' pencil ' of a Nernst lamp is made 
 chiefly of zirconia, another earth ; and here, again, unless 
 the zirconia is mixed with a trace of some other oxide, it 
 will not glow very brightly when a current of electricity 
 is passed through it. In all these cases there is almost 
 certainly chemical change, and also, no doubt, evolution of 
 corpuscles of electricity which set the ether vibrating and 
 so produce light and heat. 
 
 It may be asked : ' Do substances not lose weight when 
 corpuscles are being shot out ? ' Professor Landolt, of 
 Berlin, has been making experiments on the gain or loss 
 of weight when a weighed quantity of substances capable 
 of chemical change are mixed in a closed vessel ; and he 
 finds that in many cases there is a minute loss of weight. 
 Perhaps that is due to the escape of corpuscles ; but too few 
 experiments have been made to allow of a definite answer. 1 
 
 Perhaps, too, the corpuscles when expelled are not 
 moving very rapidly, and are thus absorbed by the sides 
 of the vessel in which the reaction takes place ; and this 
 
 1 He has since shown that there is no change of weight. 
 
128 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 may also be the case with flames. A flame, however, if 
 brought near an object containing an electric discharge 
 will discharge it; and this may possibly be due to the 
 action of electric corpuscles on the charged object. 
 
 It will be seen, then, that we do not know yet with 
 certainty what flame is, but we are getting on the track. 
 And the direction in which to make experiments is clear. 
 Whosoever asks shall receive, but he must ask sensible 
 questions in definite order, so that the answer to the first 
 suggests a second, and the reply to the second suggests a 
 third, and so on. If that course be followed, it will 
 certainly result in discoveries, many of which may be 
 important and lead to inventions of great practical value. 
 For, indeed, an invention is often definable as a method 
 for utilising a discovery. 
 
THE BECQUEREL RAYS 1 
 
 IT is remarkable how the writings of ancient authors often 
 contain a forecast of subsequent discoveries. Puck's pro- 
 jected girdle round the earth, which was promised com- 
 pletion in forty minutes, has been surpassed many hundred 
 times by the rate of the electric current in a telegraph- 
 wire ; and Robert Boyle's suggestions regarding the nature 
 of the air are on the high-road towards verification. He 
 wrote, about the year 1670: 'Our atmosphere, in my 
 opinion, consists not wholly of purer aether, or subtile 
 matter which is diffused thro' the universe, but in 
 great number of numberless exhalations of the terr- 
 aqueous globe; and the various materials which go to 
 compose it, with perhaps some substantial emanations from 
 the celestial bodies, make up together, not a bare indeter- 
 mined feculancy, but a confused aggregate of different 
 effluvia.' 
 
 Up to 1894, it was supposed that our atmosphere con- 
 sisted mainly of the two gases, nitrogen and oxygen, together 
 with minute quantities of carbonic acid, water- vapour, 
 ammonia, peroxide of hydrogen, and ozone ; but in that 
 year it was shown to contain a not inconsiderable amount 
 of an inactive gas, argon ; and crude argon has since been 
 found to contain minute quantities of no fewer than four 
 other similar gases. Small traces of hydrogen have also 
 been discovered in air; although a large percentage of 
 
 1 An article which appeared in the Contemporary Review, 1902. 
 
 I 
 
130 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 hydrogen would render air explosive (for water is formed 
 with explosive violence when hydrogen and oxygen com- 
 bine), yet traces of hydrogen may coexist with oxygen 
 without combination, except when the mixture is actually 
 in contact with a flame. 
 
 These, however, are not the only constituents of the 
 atmosphere ; and in the following pages an account will 
 be given of certain phenomena which render it exceed- 
 ingly probable that still more ' subtile matter ' is on the 
 eve of discovery. 
 
 In order to follow the course of events, it is first neces- 
 sary to devote some attention to the supposed nature of 
 light. Owing to its being perceived by our special organ 
 of sense, the eye, it early attracted attention. At first 
 believed to consist of corpuscles, shot out from the lumin- 
 ous body, it is now recognised as arising from the vibra- 
 tions of a medium pervading all space, termed ether ; and 
 the propagation of light takes place much as waves spread 
 in a pond, except in this : the particles of ether, unlike 
 the waves of water, are not restricted in their motion to 
 one plane, but the oscillations may take place in all direc- 
 tions at right angles to the direction of propagation. 
 There appears, however, to be no limit to the mode or 
 magnitude of the ethereal waves ; and though it cannot be 
 positively stated that the wave-motion ever takes place, 
 like sound waves, in the direction of propagation, still that 
 mode of propagation of waves is not excluded. It is cer- 
 tain, however, that such a mode of transmission does not 
 correspond with the nature of light, which consists wholly 
 of transverse vibrations. 
 
 Just as it is possible to measure the distance between 
 the crests of the waves of the sea, so it is possible to deter- 
 mine the distance between the crests of the waves of light, 
 or in other words, to measure the wave-length of light. 
 And it has been discovered that all the visible rays of 
 
THE BECQUEREL RAYS 131 
 
 light are comprised in less than an octave; that is, the 
 longest visible waves are not twice as long as the shortest 
 visible. Their length, moreover, is not inconceivably 
 minute. The twenty-fifth part of an inch, or a millimetre, 
 although a small distance, is easily seen with the naked 
 eye ; indeed, the twentieth part of that length can still be 
 estimated without the aid of a lens. The average length 
 of a light- wave is about the hundredth part of that dis- 
 tance, or about the two-thousandth of a millimetre. The 
 thousandth part of a millimetre is termed a micron, the 
 symbol for which is the Greek letter //, ; the wave-length 
 of deep red light is f/z, and of violet light f//,. 
 
 There are, however, ethereal waves which cannot be 
 seen. Those of greater wave-length give rise to the sensa- 
 tion of heat ; they are termed ' infra-red ' waves ; while 
 those of shorter period are accessible to photography, for 
 they change the nature of the compounds of silver which 
 form the sensitive coating of a photographic plate, and 
 can thus be recognised ; they are termed ' ultra-violet ' 
 waves. One of the difficulties of tracing the existence of 
 the short wave-lengths by photography consists in the 
 absorptive power which glass and air have for such waves. 
 A pane of glass, though transparent to ordinary light 
 waves, is nearly opaque to ultra-violet waves. Quartz or 
 crystal, of which spectacle-lenses are generally made, is 
 much more transparent to vibrations of short wave- 
 lengths ; but even quartz has its limits. By an ingenious 
 contrivance for exposing a sensitive plate in a vacuum, so 
 that the absorption of the air did not influence the result, 
 Schumann succeeded in chronicling the existence of waves 
 only -^Q/JU in length. On the other hand, Langley, by 
 means of an exceedingly delicate apparatus for detecting 
 heat-vibrations, termed a bolometer, has detected waves 
 as long as 30 p. Between that wave-length and one two 
 hundred times as great, six millimetres, there is a gap in 
 
132 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 our knowledge ; the longer waves are the vibrations the 
 discovery of which was due to Hertz, which are produced 
 by electric oscillations, and which are now being utilised 
 for telegraphy without wires. 
 
 It is, however, with the shorter, and not with the longer 
 vibrations, that we have to do. These are not incom- 
 mensurable with the dimensions of a molecule, for the 
 larger molecules are believed to be about the millionth 
 of a millimetre in diameter, or about one hundredth of 
 the shortest wave-length which has been measured. And 
 just as an interposed grating offers little opposition to the 
 course of a large wave of water, while it will stop ripples, 
 so matter is sufficiently fine-grained not to oppose the 
 spread of a Hertzian wave of great wave-length, although 
 it may stop light and other vibrations of shorter wave- 
 length. It is known, indeed, that the signals of wireless 
 telegraphy are not blocked by material obstacles such as 
 houses, or even hills, while a very thin slice of brick or 
 stone is opaque to light. 
 
 When two thin strips of gold-leaf are suspended from a 
 glass support, and given an electric charge, they diverge, 
 owing to the repulsive force between the charges of elec- 
 tricity which they contain. They will remain apart for 
 an indefinite time, provided the charge cannot escape 
 through the support. But on exposure to ultra-violet 
 rays, the electroscope, if charged with negative electricity, 
 is at once discharged, and the leaves fall together. The 
 electricity finds some means of leaving the leaves of gold 
 and they drop, under the action of gravity. The rays do 
 not, however, discharge a positively charged electroscope. 
 This is one of the most characteristic properties of the 
 ultra-violet rays, and, as will shortly be seen, of rays from 
 sources other than luminous bodies. This fact was dis- 
 covered by Hertz. 
 
 The Becquerel family has contributed much to our 
 
THE BECQUEREL RAYS 133 
 
 knowledge of the phenomena of radiation, and furnishes 
 as conspicuous an example as the Herschels of the her- 
 edity of a scientific faculty. Antoine Charles, born in 
 1788, was famous for his electric researches; Edmond, his 
 son, born in 1820, was author, with his father, of a treatise 
 on Electricity and Magnetism, and investigated the phe- 
 nomenon of phosphorescence, of which more anon ; and 
 Henri Becquerel, born in 1852, while engaged in extend- 
 ing his father's work, made the wonderful discovery of 
 the emission of rays from certain minerals containing 
 the rare metals uranium and thorium. We must first, 
 however, consider Edmond Becquerel's work. 
 
 Certain substances, after illumination, do not at once 
 cease to give back light, but continue to glow, even after 
 the source of light has been removed. Such substances, 
 one of the best known of which is fluor-spar, are called 
 phosphorescent. Some years ago, an attempt was made to 
 utilise one of such substances a carbonate of lime con- 
 taining traces of sulphide of manganese under the name 
 of ' luminous paint.' Another class of substances has the 
 property of transforming the vibrations they receive when 
 illuminated into vibrations of a different period; among 
 these are extract of horse-chestnut, and many artificial 
 colouring-matters, one of the most striking being the 
 lovely pink dye, eosin. Such bodies do not continue to 
 emit light after excitation ; they were differentiated from 
 the former by Edmond Becquerel, and are termed fluor- 
 escent. The tendency of these substances is to convert 
 short wave-lengths into longer ones. Thus a solution of 
 acid sulphate of quinine, which is perfectly colourless by 
 transmitted light, is opaque to ultra-violet rays. It reflects 
 them, and at the same time increases the wave-length ; 
 hence by reflected light the solution appears to possess a 
 violet shimmer. 
 
 It was in 1838 that Faraday investigated the luminous 
 
134 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 appearance which accompanies the passage of a high- 
 tension electric current through rarefied gases. Each gas 
 gives out a soft, coloured light, totally different from the 
 lightning-like sparks which pass between the positive and 
 negative poles through gases at ordinary atmospheric 
 pressure. The pressure must be reduced to about one- 
 hundredth of its normal amount before such phenomena 
 begin to appear; but the actual reduction of pressure 
 depends on the particular gas submitted to the dis- 
 charge. Under such conditions hydrogen glows with a 
 red light ; air with a pale violet glow ; and carbonic acid 
 has a steel blue appearance. The resistance of such 
 rarefied gases to the passage of the electric current is 
 much less than of gases at atmospheric pressure. As with 
 solid conductors, it depends on the distance between the 
 poles and the particular kind of matter employed. 
 Hittorf, the eminent electrician, Professor in Miinster, 
 was the first to conduct experiments at still lower 
 pressures, on still more rarefied gases, and he noted an 
 increase in the resistance of the gas to the passage of 
 electricity. Further, he observed that from the negative 
 electrode, or cathode, the glow proceeded in straight lines, 
 so as to cast the shadow of an interposed object on the 
 opposite wall of the tube. He discovered, too, that such 
 rays can be deviated by a magnet, a discovery made for 
 the electric arc by Sir Humphry Davy in 1821. Sir 
 William, then Mr., Crookes took up this subject in 1878, 
 simultaneously with M. Goldstein, and has made it 
 popular, by reason of the ingenious experiments which he 
 devised to exhibit the rectilinear course of these rays. 
 He devised a theory, moreover, to account for the recti- 
 linear path, namely, that the electric current when it 
 leaves the negative pole attaches itself to the molecules of 
 gas, which, projected with great velocity, will pursue a 
 parallel path, if the cathode is a flat piece of metal, or can 
 
THE BECQUEREL RAYS 135 
 
 be focussed to a point, if the cathode be given the form of 
 a concave mirror. Objects placed in the focus of such a 
 mirror are bombarded, according to Sir William, and may 
 be heated to whiteness by the impacts they receive from 
 the prodigious number of moving molecules. Goldstein, 
 on the other hand, conceived the phenomena to be due to 
 a transmission of energy, apart from the conveyance of 
 material particles ; but he gave no precise definition of the 
 nature of this transmitted energy. In 1883, however, 
 Professor Wiedemann of Leipzig made the suggestion 
 that possibly such ' cathode rays/ as the rectilinear dis- 
 charges have since been termed, are composed of radia- 
 tions of very short wave-length, shorter even than those 
 of the most ultra-violet light. The same conception was 
 held by Lenard. But while the cathode rays are deviated 
 by a magnet, light waves are uninfluenced ; and this forms 
 an argument in favour of the former being due to pro- 
 jected particles. The suggestion has also been made, but 
 on no sufficient grounds, that these phenomena are attri- 
 butable to a longitudinal vibration of the ether, the waves 
 being thus analogous to sound-waves in air alternate 
 condensations and rarefactions; or to choose a visible 
 analogy, the longitudinal vibrations of a spiral spring, in 
 which the coils periodically come closer together at one 
 point of space, and then recede and become wider apart. 
 A fourth hypothesis, similar to, yet differing from that of 
 Crookes, is held by Professor J. J. Thomson of the 
 Cavendish Laboratory, Cambridge. His view, which 
 appears to be well supported by experimental evidence, 
 is that each molecule of gas, in absorbing its electric 
 charge, dissociates, or splits up, into two or more charged 
 atoms or groups of atoms. Such charged portions of 
 matter have long been taken for granted as existing 
 during the passage of an electric current through a con- 
 ducting liquid, and were named by Faraday, ions, or 
 
136 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 travellers. An important argument in favour of this 
 contention is, that the heat developed in such tubes is 
 proportional to the intensity of the current, and not to the 
 square of the intensity, as would be the case were the 
 passage of electricity one of ordinary conduction. Thomson 
 attributes the heat to the recombination of the ions to 
 molecules, after discharge ; and the number of ions would 
 obviously be proportional to the intensity of the current 
 and not to its square. 
 
 Goldstein and Crookes both thought that ordinary 
 matter, such as glass or metal, was opaque to such 
 cathode-discharges ; but Lenard, following a suggestion of 
 Hertz's, carried out at Bonn a beautiful series of experi- 
 ments, which showed that the cathode rays could pass 
 through a thin piece of aluminium foil, and be prolonged 
 outside of the exhausted tube. Not only could they pass 
 through ordinary air, although not to such a distance as 
 through rarefied gases, but they also passed through a 
 vacuum as perfect as could be produced by a mercury- 
 pump, aided by intense cold to condense mercury- vapour 
 out of the empty space. It appeared that the absorbing 
 power of different gases is proportional to their specific 
 mass. 
 
 The velocity of propagation of such cathode rays has 
 been measured by an ingenious process by Professor J. J. 
 Thomson. It is found to be approximately 200 kilo- 
 metres, or about 124 miles a second. This, however, is 
 enormously less than the velocity of light or of electric 
 waves through the ether, which approximates to 180,000 
 miles a second. The accidental discovery by Professor 
 Eontgen in 1896 that some flakes of platinocyanide of 
 barium, placed near a Hittorf tube which was wrapped up 
 in black paper, emitted a phosphorescent light, led to a 
 great development of the subject. It was soon discovered 
 that even behind a book of 1000 pages, or a plate of 
 
THE BECQUEREL RAYS 137 
 
 aluminium half an inch thick, or a wooden board, lumin- 
 escence was still produced. Rontgen investigated the 
 transparency of various objects, and soon discovered that 
 while skin and flesh are nearly transparent to these 
 radiations, bone is comparatively opaque, and may be 
 made to throw its shadow on a photographic plate or on a 
 screen covered by phosphorescent material. The surgical 
 bearing of this discovery was at once evident ; and by help 
 of ' skiographs ' or shadow-writing the presence of a bullet 
 embedded in the tissue can be recognised, and its exact 
 situation localised ; and in cases of fractures of bones, 
 their exact shape can be made out, and they can be 
 successfully set, for it is always possible to examine the 
 position of the fractured ends through envelopes of 
 bandages, which themselves are nearly transparent to 
 Rontgen or X-rays. 
 
 One of the most remarkable properties of these rays is 
 that they cannot be refracted by passage through a prism, 
 nor apparently reflected from any object, however smooth 
 and well-polished, nor can they be polarised. They are, 
 however, absorbed by different substances unequally, and 
 apparently the denser the substance the greater its absorb- 
 ing power. 
 
 It might be supposed at first blush that the X-rays of 
 Rontgen were identical with cathode rays. But if this 
 were the case the X-rays should pass straight from the 
 cathode through the walls of the tube, and proceed in a 
 straight line ; as a matter of fact, their point of origin can 
 be displaced with a magnet, and if a spherical bulb be 
 used to contain the cathode, each point on the bulb is a 
 centre of emission, sending its radiations in all directions. 
 Now Lenard had recognised that cathode rays could be 
 differentiated into two distinct kinds. Suppose that they 
 were made to pass through a hole in a block of lead, and to 
 impinge on a photographic plate, if a magnet were placed 
 
138 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 at one side, not only was there the image of a circle 
 exactly opposite the hole, but also, at some distance from 
 the circular spot, a diffused drawn-out impression, as if 
 some of the rays had been unequally deviated by the 
 magnet, and had impressed the plate separately. It is 
 therefore probable that cathode rays contain some 
 X-rays. 
 
 The wave-length of light can be measured by reflection 
 from a metal plate on which from 14,000 to 25,000 parallel 
 lines are ruled in each inch; such a prepared plate is 
 termed a ' grating ' ; the modern gratings, which are 
 wonderfully accurately ruled, are made by Mr. Brashier 
 of Alleghany, New York State, by means of apparatus 
 devised by the late Professor Rowland of Baltimore. 
 Careful measurements by M. Perrin have proved that if the 
 X-rays are due to ethereal vibrations at all, these cannot 
 possess a wave-length greater than 0*04 /JL, that is, less than 
 half the shortest- waved ultra-violet vibrations which have 
 ever been photographed. 
 
 Again, when light is passed through a slice cut from 
 a crystal of tourmaline it is said to be polarised ; it can 
 pass through a second plate of tourmaline if held in a 
 particular position, but if the second plate be rotated so 
 that its second position is at right angles to its first, the 
 light is cut off, and fails to pass through the second plate. 
 M. Becquerel found that X-rays cannot be polarised ; they 
 pass easily through plates of tourmaline in whatever 
 position relatively to each other they be placed. On the 
 other hand, the rays emitted by phosphorescent bodies, 
 which may be termed the Becquerel rays, are capable of 
 polarisation. Hence they cannot be identical with X- or 
 with cathode rays. 
 
 Lastly, it will be remembered that ultra-violet rays 
 discharge negatively electrified bodies; they are without 
 rapid action on bodies possessing a positive charge. But 
 
THE BECQUEREL RAYS 139 
 
 X-rays discharge electrified bodies equally well, whether 
 they be charged positively or negatively. - 
 
 There is accordingly a certain degree of probability in 
 favour of the view that cathode rays are due to molecular 
 or ionic bombardment ; but they are generally mixed with 
 X-rays, which are apparently independent of matter for 
 their propagation, and are therefore to be considered as 
 due to disturbances of the ether. Ultra-violet rays, on 
 the other hand, must be ethereal waves of very short 
 wave-length ; but they have the power of splitting gaseous 
 molecules into charged atoms or groups of atoms, termed 
 ions. It may be calculated, too, that the atoms conveying 
 cathode-rays have a velocity of 124 miles a second; it 
 would follow that of such atoms a single gram, or about 
 one- thirtieth of an ounce, must have the same energy as 
 a locomotive of 80 tons weight rushing at the rate of 
 50 miles an hour ! No wonder, .then, that they penetrate 
 thin sheets of metal and embed themselves in glass. 
 
 In 1896 M. Poincare, the well-known mathematician, 
 suggested that all fluorescent substances might emit 
 Rontgen rays; being guided to this guess by the hypo- 
 thesis that it is the glass, against which the Rontgen rays 
 strike, which phosphoresces and emits the rays. This 
 suggestion was almost at once verified by M. Charles 
 Henry, when he discovered that sulphide of zinc, a sub- 
 stance which shows marked phosphorescence, greatly 
 increases the effect of X-rays when placed in their path. 
 M. Henri Becquerel, too, in the same year, found that rays 
 were emitted from a compound of the metal uranium, 
 which affected a photographic plate wrapped in black 
 paper, sufficient to exclude rays of direct sunlight. This 
 power to affect a sensitised plate persists long after all 
 visible phosphorescence ceases. Moreover, it is unneces- 
 sary to expose uranium salts to light before they are 
 capable of producing a photographic image, for these 
 
140 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 compounds may be prepared in the dark and still possess 
 actinic power. And the rays emitted from them have the 
 power of discharging both positively and negatively 
 electrified bodies. Not merely salts of uranium possess 
 this property, but even metallic uranium itself, a dark- 
 coloured, brittle metal, which emits sparks of fire when 
 shaken in a bottle, a phenomenon due probably to 
 oxidation. 
 
 Shortly after this discovery of Becquerel's, Madame 
 Curie, a Polish lady working in Paris, discovered that a 
 certain specimen of pitchblende, the common ore of 
 uranium, possesses the properties of uranium, and in 
 greater measure. Pitchblende, though consisting mainly 
 of an oxide of uranium of the formula U 3 8 , contains 
 small amounts of other elements. On separating these, 
 Monsieur and Madame Curie found that the bismuth 
 obtained from this source is particularly radio-active, 
 while ordinary bismuth shows no trace of that property. 
 Attributing this behaviour to its containing a new element, 
 they patriotically named it ' polonium/ in allusion to 
 Madame Curie's nationality. But it was not long before 
 they discovered that it was not only the bismuth which 
 exhibited radio-activity, but also the barium ; and they 
 inferred the presence of a second element, naming it 
 'radium.' A third substance has also been separated 
 from the same uranium ores by Debierne, who, following 
 precedent, has termed it 'actinium.' It appears to be 
 associated with another element, titanium, contained in 
 pitchblende ; and thorium, an element whose compounds 
 were discovered to possess radio-activity by G. C. Schmidt, 
 must be added to the list. We have therefore at present 
 no fewer than four radio-active substances : polonium, 
 associated with bismuth ; radium, with barium ; actinium, 
 with titanium ; and thorium. Associated with thorium is 
 a much more powerfully radio-active material, to which 
 
THE BECQUEREL RAYS 141 
 
 the name radio-thorium was applied by its discoverer, 
 Otto Hahn. 
 
 Besides the properties already mentioned, radium, and 
 presumably the others, have the curious property of 
 changing a spark-discharge from an electric machine or 
 a Ruhmkorffs coil into a violet glow-discharge; the 
 interposition of a piece of lead, however, re-establishes 
 the spark-discharge ; and if barium bromide containing 
 radium be held on the forehead between the closed eyes 
 in a dark room, a distinct luminous haze is visible after 
 a few seconds. The actinium rays, indeed, are said to be 
 100,000 times as powerful as those of uranium. Very 
 powerfully radio-active preparations of barium chloride 
 and bromide are now manufactured by various firms by 
 processes devised by Madame Curie and by Professor 
 Giesel. 
 
 A new light has been thrown on all these phenomena 
 by Professor Rutherford, who has found that thorium 
 compounds give out an ' emanation,' which may be likened 
 to one of Boyle's ' exhalations of the terraqueous globe.' 
 Dr. Russell had previously discovered that photographic 
 plates are affected by hydrogen dioxide vapour, which 
 appears to be produced in small amount under the most 
 varying conditions ; but Rutherford's exhalations persisted 
 under treatment which would have been fatal to hydrogen 
 dioxide ; moreover, these emanations rapidly discharge 
 electrified bodies, a property which hydrogen dioxide does 
 not possess. The existence of such emanations (of which 
 more hereafter) must be borne in mind in forming a 
 judgment of the statements made about these various 
 radiations. 
 
 Radio-active substances can communicate transitory 
 radio-activity to all kinds of matter, metals, glass, paper, 
 etc., which then for a short time possess radio-activity 
 equal to ninety times that of uranium. They lose the 
 
142 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 property more rapidly, however, when heated or washed. 
 Even distilled water acquires radio-activity, when placed 
 near radium chloride under a glass bell-jar; the water 
 rapidly loses its power in an open vessel after removing 
 it from the proximity of the radium; and even when 
 sealed into a glass tube it loses power after a few days. 
 On the other hand, a solution of a radium salt (e.g. radio- 
 active barium bromide) loses activity on exposure to air, 
 but regains it on being kept in a sealed tube. 
 
 MM. Curie and Debierne find that this induced radio- 
 activity is greatly increased when the radium compound 
 is placed in a small open vessel under a bell-jar, and sheets 
 of various materials are exposed under the same cover. 
 Even behind leaden screens the activity is induced. If 
 they are in contact with the vessel containing the radium, 
 or with the walls of the enclosed space, only the exposed 
 surfaces are rendered radio-active. The activity of such 
 sheets of material induced by a specimen of barium 
 bromide containing radium, and of which the mean atomic 
 weight of the mixture of metals is 174 instead of 137 (that 
 of barium), is 8000 times that of a piece of uranium of the 
 same dimensions. As long as the sheets are left in the 
 enclosure, the activity persists; if removed, it disappears 
 in a few days. This conveyance of induced radio-activity 
 is equally brought about if the radium compound is 
 placed in one vessel, and the sheets in another, connected 
 with the former by means of a capillary tube ; but if 
 communication between the vessels is cut off, the trans- 
 mission of activity ceases. 
 
 It is very remarkable that this transference of radio- 
 activity is confined to radium and actinium; polonium 
 compounds do not appear to possess the property of 
 giving off emanations. It may be that this difference 
 is connected with the fact discovered by Becquerel that 
 while his rays (those of radium and actinium, probably), 
 
THE BECQUEEEL RAYS 143 
 
 like cathode rays, are deviable by a magnet, those of 
 polonium resemble X-rays in being unaffected. Curie, 
 on the other hand, states that both deviable and undevi- 
 able rays are emitted from radium as well as from 
 polonium, and that the non- deviable rays are stopped by 
 a piece of thin aluminium foil. None of these rays appear 
 to be polarisable, nor do they show refraction when passed 
 through a prism. 
 
 Becquerel also discovered that air, left in contact with 
 some radio-active substances, discharges electrified bodies ; 
 indeed, it is impossible to charge an insulated conductor 
 in a room in which any such preparations have been 
 exposed. This power of inducing air to discharge electri- 
 fied bodies persists for at least a year, even although the 
 preparation has been kept in the dark all the time; it 
 cannot therefore be supposed that light-energy is in any 
 way transformed into such radiations. 
 
 In Curie's experiments on induction it was found that 
 provided the vessel containing radium was kept vacuous, 
 the emanations had no longer the property of inducing 
 radio-activity in sheets of metal, etc., exposed in the same 
 vessel. It appears possible, therefore, to pump off the 
 radio-active matter ; and the natural conclusion is that 
 it is a gas. The gaseous matter has been collected, or at 
 least air charged with it, and it displays marked chemical 
 action, as well as high radio-activity. It converts oxygen 
 into ozone, and the glass vessels which contain it, if 
 formed of soda-glass, turn violet, and then black, owing 
 to some change. Becquerel, too, remarks on the destruc- 
 tive action of radium rays on the skin; they discolour 
 rock-salt, change yellow phosphorus to red, and destroy 
 the germinating power of mustard and cress seeds. 
 
 On the hypothesis that the radiation of radium is 
 produced by the escape of material particles which 
 bombard the walls of the containing vessel, the velocity 
 
144 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 of such particles can be determined by a device which 
 may be illustrated thus : Imagine a bullet fired from a 
 rifle placed horizontally, at some little distance above the 
 ground ; the bullet will be attracted to the earth, and will 
 fall to the ground after it has gone a certain distance. 
 The factors which determine the spot at which it will 
 strike the ground (excluding the retarding influence of 
 air) are its speed, and the attraction of the earth. If the 
 attraction is known, the speed can be calculated. This 
 analogy illustrates, although imperfectly, the method of 
 arriving at the speed of these impelled particles. They 
 are deviated by a magnetic field, and have a trajectory 
 just as a rifle-bullet has; and their speed has been cal- 
 culated by Becquerel at 160,000 kilometres or 100,000 
 miles per second. This estimate differs greatly from the 
 one previously mentioned for cathode rays. 
 
 In conclusion, it has been suggested that the existence 
 of such radiations and emanations may be attributed to 
 the existence of ' electrons ' in the free state. An electron, 
 it may be explained, is an electric charge which attaches 
 itself to an atom of an element, thereby converting it into 
 an ion. The act of solution in water of such a substance 
 as common salt is now currently held to cause the atom 
 of sodium to separate from the chlorine atom, while each 
 acquires an electric charge, the sodium combining with a 
 positive electron, the chlorine with a negative one, thus : 
 NaCl + water + = Na + water + Cl + 
 water; the neutral molecule of electricity, consisting of 
 two oppositely charged electrons being thus dissociated. 
 Now it is conceivable that such a substance as pitchblende 
 or its radio-active constituents may combine with one of 
 the electrons, liberating the other. It has, indeed, been 
 shown by the Curies that radium rays charge negatively 
 the bodies which receive them, while the radium prepara- 
 tion acquires a positive charge. 
 
THE BECQUEREL RAYS 145 
 
 Whatever be the true explanation of these mysteries, 
 it cannot be denied that they form the beginnings of 
 what may, and almost certainly will, affect the material 
 future of the human race. When we consider the begin- 
 nings made by Gilbert, by Franklin, by Volta, and by 
 Faraday, and contrast them with the outcome of these 
 discoveries, the electric telegraph, and the dynamo 
 machine, we cannot avoid the inference that the future 
 has in store even greater developments than these. It 
 is true that investigators like Hertz, Lenard, Becquerel, 
 and the Curies do not make practical application of their 
 discoveries; but there is never any lack of men who 
 discover their practical value, and apply them to ends 
 useful to mankind. All the more reason, therefore, that 
 every encouragement should be given to the investigator, 
 for it is to him that all our advances in physical and 
 material well-being are ultimately due. 
 
 K 
 
WHAT IS AN ELEMENT? 
 
 IT was for long held that things around us, animals, 
 vegetables, stones, or liquids, partook of the properties of 
 one or more of the elements Fire, Air, Earth, or Water. 
 The doctrine was a very ancient one; it probably 
 originated in India; it reached our forefathers through 
 the Greeks. Fire was supposed to be ' hot and dry ' ; air, 
 ' hot and moist ' ; water, ' cold and moist ' ; and earth, 
 'cold and dry.' And substances which partook of such 
 qualities were supposed to contain appropriate amounts 
 of the elements, which conferred on them these pro- 
 perties. 
 
 But in the reign of Charles n. of England, about the 
 year 1660, ^Robert Boyle, an English philosopher and 
 chemist, restored to the word element the meaning which 
 its derivation implies. ' Element,' or elemens in Latin, is 
 supposed to be derived from the three letters L M N ; and 
 to denote that, as a word is composed of letters, so a com- 
 pound is composed of elements. Boyle, in his celebrated 
 work The Sceptical Chymist, restricted the use of the 
 word element to the constituent of a compound ; and 
 that is the meaning which is still attached to the 
 term. 
 
 It has often been asked : Does a compound contain an 
 element ? Are the elements actually in the compound ? 
 If this means, for example, that iron is present as iron in 
 
 147 
 
148 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 iron-rust, the answer must be: No. The properties of 
 rust are wholly different from those of iron; no iron 
 particle can be detected in the rust by any tests which are 
 suitable for the recognition of the metal as such. But if 
 it is meant that iron if exposed to damp air changes into 
 rust, and that by suitable treatment metallic iron can be 
 extracted from rust, then the answer must be in the 
 affirmative. 
 
 The fact that an element, when it combines with other 
 elements, entirely loses its original properties, led to the 
 not unnatural supposition that it should be possible to 
 change an element into another, or to transmute it. Long 
 before the notion of ' element ' was formulated by Boyle, 
 innumerable attempts had been made to convert one 
 metal into another ; and, indeed, it would appear on the 
 face of it to be much easier to transmute lead into silver 
 or gold than to convert it into the yellow earthy powder 
 which it becomes when heated in air. For on the old 
 doctrines, the properties of gold its lustre, its ductilit} 7 , 
 its melting in the fire were much more similar to those 
 of lead than the properties of litharge or oxide of lead, 
 produced by heating lead to redness in air. After Boyle's 
 day, however, it gradually came to be seen that certain 
 substances resisted all such attempts to change them into 
 others without increasing their weight. For example, all 
 changes in nature not of a temporary and evanescent charac- 
 ter which iron can be made to undergo, are accompanied 
 by an increase in the weight of the iron ; they are produced 
 by the combination of iron with other elements, and the 
 addition of another element to iron invariably increases 
 the weight, for the weight of the combining element is 
 added to that of the iron, and the result is a compound 
 differing in properties from iron. It was slowly discovered 
 that about seventy substances must be classed as elements 
 the minimum number of the present day is seventy- 
 
WHAT IS AN ELEMENT ? 149 
 
 four and of these ten are gases, two are liquids, eight 
 elements are usually classed as non-inetals, since they do 
 not possess the lustre and some of the other properties of 
 rnetals ; and the remainder are metals. These substances 
 are classified as elements solely because no attempts to 
 convert one into another have up till now been successful ; 
 not because such change is in the nature of things im- 
 possible. But inasmuch as the properties of these 
 elements, and the changes which they undergo on 
 being brought together with other elements or compounds, 
 have been the subject of an enormous number of experi- 
 ments, and because no hint of transmutation has been 
 found, the conclusion as regards the immutability of 
 elements has been arrived at. Hence the ' transmutation 
 of elements ' has generally been regarded as impossible, 
 and as unattainable as perpetual motion, or as the ' quad- 
 rature of the circle.' 
 
 Speculation, however, has a deep fascination for many 
 minds ; and it has been often held that it is not im- 
 possible that all elements may consist of a primal 
 substance 'protyle,' as it has been called in different 
 states of condensation. It will be worth while to spend 
 a few minutes in considering the reasons for this 
 opinion. 
 
 About the beginning of last century, John Dalton 
 revived the old Greek hypothesis that all matter, elements 
 included, consists of atoms or minute invisible particles ; 
 these, of course, like the matter which is formed of them, 
 possess weight. Although they are so minute that any 
 attempt to determine their individual weight would be 
 out of the question, Dalton conceived the idea that at 
 least their relative weights could be determined, by ascer- 
 taining the proportions by weight in which they are pre- 
 sent in their compounds. The compound of hydrogen 
 and chlorine, for example, commonly known as muriatic 
 
150 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 or hydrochloric acid, consists of one part by weight of 
 hydrogen combined with 35J parts by weight of chlorine ; 
 and as it is believed to contain one atom of each element, 
 it follows that an atom of chlorine is 35 J times as heavy 
 as an atom of hydrogen. On the same principle, the 
 relative weights of the atoms of other elements were 
 determined. And so, taking the weight of the lightest 
 atom, hydrogen, as unity, the atom of nitrogen weighs 
 14 times as much, of oxygen 16, of iron 56, of lead 207, 
 and so on. 
 
 Attempts to classify elements according to their proper- 
 ties soon followed ; and at first the divisions were some- 
 what arbitrary. The non-metals were distinguished from 
 the metals by their lack of lustre, their feeble power of 
 conducting heat, and the fact that their oxides when 
 mixed with water generally formed acid substances, while 
 those of the metals were earthy, insoluble powders. Cer- 
 tain of the metals, which either do not unite with or are 
 difficult to unite with oxygen at a red heat, were called 
 ' noble ' metals ; others, which are at once attacked by 
 water, such as sodium and potassium, and which give 
 soapy liquids with a harsh taste, were named ' metals 
 of the alkalies/ and so with the rest. In 1863, however, 
 Mr. John Newlands, a London analyst, was successful in 
 arranging the elements in groups, so that each element 
 in a horizontal column showed analogy with others in the 
 same column. He found that by writing the names of 
 the elements in horizontal rows, beginning with the one 
 of lowest atomic weight, each eighth element possessed 
 properties similar to those of the elements which pre- 
 ceded or followed it in the vertical columns. And in 
 general the composition of the compounds of such 
 similar elements was similar. The first two lines of 
 such a table are reproduced here, so as to show what is 
 meant : 
 
WHAT IS AN ELEMENT ? 151 
 
 Name . . Lithium. Beryllium. Boron. Carbon. Nitrogen. Oxygen. Fluorine. 
 Atomic Weight .7 9'1 11 12 14 16 19 
 
 Name . . Sodium. Magnesium. Aluminium. Silicon. Phosphorus. Sulphur. Chlorine. 
 
 Atomic Weight . 23 24-4 2V1 28'4 31 32 35'5 
 
 If one were to proceed further in the same manner, we 
 should find five elements in the first vertical column 
 namely lithium, sodium, potassium, rubidium, and 
 caesium. All of these are soft metals, easily cut with a 
 knife, white in colour like silver, rapidly tarnishing in air, 
 attacked violently by water so that they either catch fire 
 or run about on the surface of the water and rapidly dis- 
 appear. Their compounds with chlorine each consist of 
 one atom of each element : for example, using Na 
 (natrium) as the symbol for one atom of sodium, and Cl 
 for one atom of chlorine, the composition of the com- 
 pound of chlorine with sodium (common salt) is expressed 
 by the formula NaCI, implying that the compound is 
 formed of one atom of each element. So with the 
 others : the chloride of lithium is LiCl, of potassium 
 KC1, of rubidium RbCl, and of cesium CsCl. They all 
 resemble common salt ; the taste is similar in all cases, 
 the salts dissolve in water, they are all white in colour, 
 they all crystallise in cubes, and possess many other pro- 
 perties in common. The oxides, too, are all powders, 
 which dissolve in water and give liquids with a soapy 
 feel and a burning taste. For these and other similar 
 reasons, all these elements are believed to belong to the 
 one class. 
 
 Let us take an example, too, from the other end of the 
 table. Fluorine, the first of the column, is a pale yellow 
 gas, with a suffocating odour. It combines instantly with 
 hydrogen, yielding a colourless gas, soluble in water, and 
 giving an acid liquid, which corrodes many metals. 
 Chlorine, the second member, is a greenish yellow gas, 
 very similar in properties to fluorine. The third member, 
 
152 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 bromine, is a dark red liquid, but at a somewhat lower 
 temperature than that of boiling water it changes into a 
 red gas, with a smell similar to that of chlorine ; iodine, 
 though a black solid at the ordinary temperature, be- 
 comes, when heated, a violet gas. Like fluorine, they all 
 form compounds with hydrogen, of the formulse HF, HC1, 
 HBr, and HI ; these are colourless gases, soluble in water. 
 
 Enough has been said to show that Newlands' method 
 of classifying the elements brings together in vertical 
 columns those that have similar properties. This method 
 was developed by a German chemist named Lothar 
 Meyer, and by a Russian named Mendeleeff, and it is now 
 universally acknowledged to be the only rational way of 
 classifying the elements. 
 
 If we consider one of the horizontal rows, we shall also 
 discover a peculiarity. The number of atoms of the 
 elements which combine with an atom of oxygen gradually 
 alters ; and if they form compounds with hydrogen, the 
 same kind of regularity can be observed. For instance, 
 the elements of the first horizontal row given above form 
 the following compounds with oxygen and hydrogen : 
 
 Name . . Lithium. Beryllium. Boron. Carbon. Nitrogen. Oxygen. Fluorine. 
 Formula of 
 
 . Oxide . . Li 2 BeO B 2 3 C0 2 N 2 fi 
 Formula of 
 
 Hydride . LiH unknown BH 3 CH 4 NH 3 OH 2 FH 
 
 The elements of the subsequent rows show similar 
 regularity. 
 
 Up till recently, no elements were known which refused 
 to combine with other elements. In 1894, however, Lord 
 Rayleigh and Sir William Ramsay discovered that 
 ordinary air contained such a gas, and they named it 
 'argon,' a Greek word which signifies inactive or lazy. 
 This gas had been overlooked because of its resemblance 
 to another constituent of the atmosphere, present in 
 nearly one hundred times greater amount nitrogen. 
 
WHAT IS AN ELEMENT ? 153 
 
 Argon cannot be made to combine, and hence it is left 
 behind when the nitrogen and oxygen have been removed 
 from the atmosphere. 
 
 Shortly after the discovery of argon, Ramsay found 
 that certain minerals when heated give off a gas similar 
 to argon, inasmuch as it forms no compounds, but with 
 a much lower atomic weight; for while argon possesses 
 the atomic weight forty, the atomic weight of helium (the 
 name given to this new gas) is only four. Now these 
 elements evidently belong to one series, for they are both 
 colourless gases, incapable of combining with other 
 elements. And it appeared almost certain that other 
 gases, similar in properties to these two, should be capable 
 of existence. And Ramsay, in conjunction with Travers, 
 spent several years in a hunt for the missing elements. 
 They heated upwards of a hundred minerals, to see 
 whether they evolved gas, and, if so, whether the gas 
 obtained was new; but although they discovered that 
 many minerals give off helium when heated, no new gas 
 was found. Mineral waters were boiled, so as to expel 
 dissolved gases ; again only argon and helium were 
 obtained. Even meteorites, or ' falling stars,' were 
 heated ; only one was found to give off gas incapable of 
 combination, and that gas consisted of a mixture of the 
 two which were already known. 
 
 As a last attempt, Ramsay and Travers prepared a large 
 quantity of argon, by removing the oxygen and the 
 nitrogen from air, and then forced the gas into a bulb, 
 dipping in a vessel immersed in a tube full of liquid air, 
 which is so cold that the argon changed to liquid. It 
 forms a colourless, mobile liquid, just like water. When 
 the liquid air is removed, the argon begins to boil. 
 
 It was hoped that the distillation of crude liquid argon 
 might separate from it other gases boiling at a lower or a 
 higher temperature ; that if it contained any other liquids 
 of lower boiling-point, these would distil over first, and 
 
154 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 could be collected separately; while any 'heavier' gases 
 would be the last to distil over*. The hope was not dis- 
 appointed at all events as regards the first expectation ; 
 for the first part of the gas which evaporated was consider- 
 ably lighter than argon and had a much lower boiling- 
 point. After a few redistillations, however, it was found 
 that liquid air was not sufficiently cold to condense this 
 light gas to liquid. But Dr. Travers was equal to the 
 emergency. He constructed an apparatus by help of 
 which hydrogen gas was condensed to liquid ; and the 
 boiling-point of liquid hydrogen is much lower than that 
 of liquid air; it is 252 - 5 C. On cooling the mixture 
 of gases which had been separated from the argon, a 
 portion only condensed, while about one- third still remained 
 as a gas ; the gaseous portion was helium, and the liquid (or 
 solid) portion evaporated into a gas which was named 
 ' neon,' the Greek word for ' new.' 
 
 It was also found that two other gases could be sepa- 
 rated from air by allowing a large quantity of liquid air 
 to boil away. These gases have a much higher boiling- 
 point than oxygen, nitrogen, or argon, and therefore they 
 remain mixed with the last drops of liquid after most of 
 the air has evaporated. They were separated from each 
 other by ' fractionation ' ; one was named 'krypton,' the 
 Greek for ' hidden ' : and the other ' xenon/ or ' strange.' 
 
 Five new gases were thus obtained ; they are given with 
 their atomic weight in the following line : 
 
 Helium, 4 ; Neon, 20 ; Argon, 40 ; Krypton, 81 '6 ; Xenon, 128. 
 
 Their position among other elements is well seen from the 
 following extract from the whole table of the elements : 
 
 Hydrogen, 1 Helium, 4 Lithium, 7 Berylium, 9*1, etc. 
 
 Fluorine, 10 Neon, 20 Sodium, 23 Magnesium, 24'3, etc. 
 
 Chlorine, 35 '5 Argon, 40 Potassium, 39 '1 Calcium, 40, etc. 
 
 Bromine, 80 Krypton, 81 Rubidium, 85*4 Strontium, 87'6, etc. 
 
 Iodine, 127 Xenon, 128 Caesium, 133 Barium, 137'4, etc. 
 
WHAT IS AN ELEMENT ? 155 
 
 It will be noticed that their atomic weights lie between 
 those of the elements in* the vertical rows ; and that they 
 separate the active elements of the fluorine group from 
 the equally active elements of the sodium group. 
 
 The discovery of these elements, however, has added 
 little to our knowledge as regards the nature of elements in 
 general, except in so far as to show that elements which 
 form no compounds can exist. It might be supposed that 
 the same agencies which are successful in splitting up 
 compounds into the elements of which they consist might 
 decompose elements into some still simpler substances ; 
 of course the elements thus decomposed could no longer 
 be called elements. And it appeared not impossible that 
 in a series of elements closely resembling each other, like 
 those of the sodium column, or the chlorine column, it 
 might be impossible to decompose those of higher atomic 
 weight into those of lower atomic weight, and perhaps 
 something else. Such agencies are : a high temperature 
 or an electric current. Water, for instance, can be decom- 
 posed into hydrogen and oxygen either by heating steam 
 to whiteness or by passing an electric current through 
 water. But it is needless to say that the elements have 
 been repeatedly exposed to the highest temperature and 
 to the strongest electric currents and yet have remained 
 elements. There are, indeed, reasons for supposing that 
 at the enormously high temperatures of the sun and of 
 the fixed stars some of our elemei|j are decomposed ; but 
 it has hitherto been impossible to reproduce such extreme 
 conditions on the earth. 
 
 The element carbon is characterised by the enormous 
 number of compounds which it forms, chiefly with hydrogen 
 and oxygen, although many other elements can be in- 
 duced to combine with it. And one instructive fact is 
 to be noticed as regards such compounds : the greater the 
 number of atoms they contain the more easily they are 
 
156 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 decomposed by heat. Indeed, some compounds are so un- 
 stable that they decompose at the ordinary temperature, 
 not into their elements, it is true, but into other com- 
 pounds of carbon, hydrogen and oxygen. Such compounds 
 are stable only at a low temperature, and the higher the 
 temperature the more readily they decompose. Judging 
 by analogy, we should expect elements of high atomic 
 weight to show tendency to decomposition, granting, of 
 course, that any element at all is capable of decomposing. 
 Now among the three elements of highest atomic weight 
 known is radium, an element belonging to the barium 
 column, of which the atomic weight is 226. This remark- 
 able substance exists in a mineral named pitchblende, 
 an oxide of uranium ; its discovery by Madame Curie, of 
 Paris, is one of the most remarkable of recent events in 
 chemical history. 
 
 The second element of high atomic weight is thorium 
 (232'5). It was noticed by Dr. Schmidt, and indepen- 
 dently by Professor Rutherford, of Montreal, that if air 
 was passed over a salt of thorium, or bubbled through its 
 solution, it carried with it an ' emanation ' which possessed 
 for a short time the power of discharging an electroscope. 
 Radium salts also give off such an emanation, or gas, 
 which, however, retains its properties for more days than 
 the thorium gas does for minutes. Uranium, the chief 
 constituent of pitchblende, too, has also the power of 
 discharging an electro^ope, but it gives off no emana- 
 tion. Its. atomic weight is 239'5 : it is the highest 
 known. 
 
 The gases evolved from compounds of thorium and 
 radium can be condensed to solid or liquid by passing 
 them through a tube cooled with liquid air. But they 
 are present in such excessively minute quantity that they 
 have never been seen, even as a minute drop. They are 
 as inert as argon, and they are members of that group of 
 
WHAT IS AN ELEMENT ? 157 
 
 elements ; and the radium gas shines in the dark, so that 
 a tube containing it gives off a whitish phosphorescent 
 light like that given off by stale fish, or like the luminosity 
 of the sea on calm summer evenings, or like the head of a 
 lucifer match if it is gently rubbed in the dark. If the 
 gas from radium is mixed with air, it is possible to see it 
 passing through a tube in the dark, and to recognise it by 
 its faint shining when it is transferred from one glass tube 
 to another. 
 
 It is very easy to remove oxygen from a mixture of 
 gases ; if a piece of the element phosphorus be heated in 
 oxygen, a solid compound of the two is formed, and all 
 oxygen can then be got rid of; or oxygen may be ab- 
 sorbed by passing the mixed gases over red-hot copper. 
 Hence it is convenient to allow the emanation from 
 radium salts to mix with oxygen rather than with air; 
 for nitrogen, the other constituent of air, is more diffi- 
 cult to remove. And it is then possible to collect the 
 radium emanation, mixed with oxygen, in a glass tube, 
 and then to absorb the oxygen, leaving only the emana- 
 tion present. 
 
 Now, as has been said, the emanation gradually loses its 
 power of discharging an electroscope. After four days it 
 requires twice as much emanation to produce the same 
 discharging effect as would be required if the emanation 
 were freshly prepared from radium salts. And the ques- 
 tion suggested itself to Mr. Soddy and Sir William Ramsay : 
 What becomes of the emanation ? Does it merely lose its 
 luminosity and discharging power, or is it changed into 
 something else ? 
 
 Chemists have long had at their disposal a means of 
 recognising almost inconceivably minute quantities of 
 matter. All substances, when made into a gas by intense 
 heat, give out light ; and that light, if passed through a 
 prism, is seen not often to be all of one kind. For example, 
 
158 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 the light given out by sodium gas at a red heat is yellow ; 
 and if passed through a slit, and then through a prism, 
 two yellow lines are seen the spectrum of sodium. 
 Similarly, potassium salts, in a spirit-lamp flame, gives 
 out a violet light ; and the prism shows us that the light 
 consists of two kinds one red and one violet. And so 
 for other elements. If the spectra of gases have to be 
 examined, they can be made to glow by passing an electric 
 discharge through a very narrow tube containing a minute 
 trace of the gas. Helium, for example, if examined in 
 this way, gives out light consisting of many colours : red, 
 yellow the most intense green, green-blue, blue and 
 violet. Hence it is easy to recognise the presence of 
 helium in such a capillary tube, by passing an electric 
 discharge through it, for the exact position of the lines 
 in its spectrum is easily recognised. 
 
 Now Ramsay and Soddy found that the emanation from 
 radium salts, though it gave out a special light of its own 
 when made luminous by an electric discharge, showed 
 none of the lines characteristic of helium. But after 
 standing for three days the yellow line of helium began to 
 be visible, and that is the one most easily seen. As time 
 went on, and as the emanation lost its self-luminosity, the 
 other lines denoting the presence of helium became dis- 
 tinctly visible. The conclusion was forced upon them, 
 therefore, that, as the emanation disappears, helium is 
 formed, or, in., other words, the emanation is changing 
 slowly into helium. 
 
 Professor J. J. Thomson, of Cambridge, has of recent 
 years been investigating the motion of particles which are 
 shot off from the negative pole when an electric discharge 
 is passed through gases ; and he has succeeded in showing 
 that some of the particles move with enormous rapidity, 
 and that they possess a weight which cannot be much 
 more than one seven-hundredth of that of a hydrogen 
 
WHAT IS AN ELEMENT? 159 
 
 atom. It is almost certain that radium salts continually 
 emit such rapidly moving particles, and it is known that 
 while doing so the temperature of the radium salt is some 
 degrees higher than that of the surrounding atmosphere ; 
 radium, therefore, is continually giving off heat. We are 
 wholly unacquainted with any similar change; these 
 properties are new. But we do know of compound sub- 
 stances which decompose with slight provocation, give off 
 a great amount of heat in doing so, and at the same time 
 are wholly converted into a large quantity of gases ; per- 
 haps the most familiar example is gun-cotton, of which 
 most of the high explosives used for blasting and in the 
 manufacture of modern gunpowder are made. The dif- 
 ferences between the two phenomena, moreover, are 
 sufficiently pronounced: gun-cotton decomposes almost 
 instantaneously, with explosive violence; radium salts 
 slowly ; gun-cotton requires to be started by the explosion 
 of a percussion-cap ; radium salts decompose spontaneously, 
 and the rate of decomposition, so far as is known, appears 
 to be independent of temperature; the amount of heat 
 evolved when gun-cotton explodes, though great in itself, 
 is' small in comparison with that evolved during the de- 
 composition of an equal weight of radium salt ; and it is 
 not known that any electrical phenomena accompany the 
 decomposition of gun-cotton. Still, it appears reasonable 
 to suspect that the two kinds of change may, after all, be 
 similar, and that the heavy atom of radium is decompos- 
 ing into the lighter helium atom. It is pretty certain 
 that helium is not the only substance produced when the 
 emanation from radium decomposes; and it is not known 
 whether radium, when it gives off its emanation, produces 
 at the same time any other decomposition product. Much 
 has yet to be discovered. Yet it must be acknowledged 
 that a distinct advance has been made, and that at least 
 one so-called element can no longer be regarded as ulti- 
 
160 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 mate matter, but is itself undergoing change into a simpler 
 form of matter. 
 
 The young student, when he learns what is known, is 
 too apt to think that little is left to be discovered ; yet all 
 our progress since the time of Sir Isaac Newton has not 
 falsified the saying of that great man that we are but 
 children picking up here and there a pebble from the 
 shore of knowledge, while a whole unknown ocean stretches 
 before our eyes. Nothing can be more certain than this : 
 that we are just beginning to learn something of the 
 wonders of the world on which we live and move and 
 have our being. 
 
ON THE PERIODIC ARRANGEMENT OF 
 THE ELEMENTS 
 
 AT the end of the eighteenth century, after the investiga- 
 tions of Black, Scheele, Priestley, Cavendish, and Lavoisier 
 began to crystallise the previous arbitrary collections of 
 chemical facts into more or less of a system, it became 
 evident that the distinguishing feature of a ' compound/ 
 as contrasted with a ' mixture,' was the invariability of its 
 composition. Early in the nineteenth century, Dalton 
 formulated his celebrated hypothesis, by means of which 
 a concrete view was gained regarding the cause of this 
 constancy and invariability of composition. Every one 
 knows that this c explanation ' consisted in the supposition 
 that the combination of two substances, one with another, 
 in definite proportions, involves the union either of one 
 atom of the one with one atom of the other, or of certain 
 small but simple numbers of atoms of the two substances. 
 The atom was regarded, not necessarily as indivisible, but 
 as not having been divided into any smaller particles. 
 The advance made by Dalton consisted chiefly in ascribing 
 to each atom a definite weight ; but as he had no data for 
 determining the absolute weight of any one atom, he was 
 obliged to content himself with relative weights, and chose 
 the smallest known to him, that of hydrogen, as an arbi- 
 trary unit. This choice has proved to be a just one, for 
 as yet no element has been discovered possessing a lower 
 atomic weight than hydrogen, although it is by no means 
 impossible that such an element may exist. 
 
 L 
 
162 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 After the convenience of Dalton's hypothesis had been 
 acknowledged, the labour of chemists was for many years 
 devoted to the determination of the relative values of the 
 ' atomic weights ' of the elements ; or, expressed in a 
 manner independent of hypothesis, of their combining 
 proportions. The name of the Swedish chemist, Berzelius, 
 is prominent in this connection. By the analysis of an 
 almost incredibly large number of compounds, he estab- 
 lished on a firm basis the constancy of composition of 
 compounds, and the law of multiple proportions. Towards 
 the 'forties, therefore, a set of numbers had been col- 
 lected, which invited an attempt to place them in order, 
 with the view of seeing whether some still more profound 
 law could not be discovered connecting the combining 
 numbers attached to them. Dobereiner, as early as 1817, 
 and again in 1829, pointed out that certain elements had 
 atomic weights which were nearly the mean of those of 
 others which were closely related to them ; thus, the mean 
 of the atomic weights of calcium and barium gives a close 
 approximation to the atomic weight of strontium ; that of 
 sodium lies near the mean of those of lithium and potassium; 
 and sulphur and tellurium similarly indicate selenium 
 as a middle element. In 1843 Gmelin, who published 
 a Handbook of Chemistry, which is still a classic, attempted 
 a classification based, not upon numerical relations, but 
 on similarity of properties. For instance, we find the 
 groups F, Cl, Br, I; S, Se, Te; P, As, Sb; C, B, Si; Li, 
 Na, K ; Mg, Ca, Sr, Ba ; and so on. In 1851 Dumas gave 
 a lecture before the British Association, in which he 
 showed that not merely is the atomic weight of bromine 
 the mean of those of chlorine and iodine, but that its 
 physical properties, such as its colour, its density in the 
 gaseous and in the liquid state, etc., are also half-way 
 between those of the allied elements. In 1852 Faraday 
 criticised Dumas' attempts as 'speculations which have 
 
PERIODIC ARRANGEMENT OF ELEMENTS 163 
 
 scarcely yet assumed the consistence of a theory, and 
 which are only at the present time to be ranked among 
 the poetic day-dreams of a philosopher'; and he pro- 
 ceeded : ' We seem here to have the dawning of a new - 
 light indicative of the mutual convertibility of certain 
 groups of elements, although under conditions which are 
 as yet hidden from our scrutiny.' 
 
 Passing over attempts by Gladstone, Cooke, Odling, 
 and Strecker, we come to the years 1863 and 1864, when 
 John Newlands, in a series of letters to the Chemical 
 News, announced what he termed the ' Law of Octaves.' 
 His actual words were : ' If the elements are arranged in 
 the order of their equivalents, with a few slight trans- 
 positions, it will be observed that elements belonging to 
 the same group usually appear on the same horizontal 
 line. It will also be seen that the numbers of analogous 
 elements generally differ, either by 7 or by some multiple 
 of 7 ; in other words, members of the same group stand 
 to each other in the same relation as the extremities of 
 one or more octaves in music. Thus in the nitrogen 
 group, between nitrogen and phosphorus there are 7 
 elements; between phosphorus and arsenic, 14; between 
 arsenic and antimony, 14 ; and lastly, between antimony 
 and bismuth, 14 also. This peculiar relationship I propose 
 provisionally to term the " Law of Octaves." ' 
 
 In 1869 and 1870, Lothar Meyer and Dmitri Mendeleeff, 
 independently of Newlands, and also of each other, 
 published papers in which they maintained that the 
 properties of the elements are periodic functions of their 
 atomic weights. This discovery goes by the name of the 
 'Periodic Law,' or better, the 'Periodic System.' The 
 arrangement of Meyer (p. 164), which differs but little 
 from that of Mendeleeff, is the one generally adopted. 
 
 If this diagram is rolled round a cylinder, it will form a 
 continuous spiral, beginning with lithium and ending with 
 
164 ESSAYS-BIOGRAPHICAL AND CHEMICAL 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 V. 
 
 VI. 
 
 VII."- 
 
 ^ VIII. 
 
 Li 
 
 
 
 
 
 
 
 
 He 
 
 
 7-03 
 
 Be 
 
 
 
 
 
 
 
 f, 
 
 
 
 9-1 
 
 B 
 
 
 
 
 
 
 
 
 
 
 11-0 
 
 c 
 
 
 
 
 
 
 
 
 
 
 12-0 
 
 N. 
 
 
 
 
 
 
 
 
 
 
 14-04 
 
 
 
 
 
 
 
 
 
 
 
 
 16-00 
 
 F 
 
 
 
 
 Na 
 
 
 
 
 
 
 19 
 
 
 Ne 
 
 
 2305 
 
 Mg 
 
 
 
 
 
 
 
 20 
 
 
 
 2436 
 
 Al 
 
 
 
 
 
 
 
 
 
 
 27-1 
 
 Si 
 
 
 
 
 
 
 
 
 
 
 28-4 
 
 P 
 
 
 
 
 
 
 
 
 
 
 31-0 
 
 S 
 
 
 
 
 
 
 
 
 
 
 32-06 
 
 Cl 
 
 
 
 
 K 
 
 
 
 
 
 
 35-45 
 
 
 A 
 
 
 39-14 
 
 Ca 
 
 
 
 
 
 
 
 39-9 
 
 
 
 40'0 
 
 Sc 
 
 
 
 
 
 
 
 
 
 
 44 
 
 Ti 
 
 
 
 
 
 
 
 
 
 
 48-1 
 
 V 
 
 
 
 
 
 
 
 
 
 
 51-2 
 
 Cr 
 
 
 
 
 
 
 
 
 
 
 521 
 
 Mn 
 
 
 
 
 Cu 
 
 
 
 
 
 
 55-0 
 
 Fe 
 
 
 
 63-6 
 
 Zn 
 
 
 
 
 
 
 56-0 
 
 Co 
 
 Ni 
 
 
 65-4 
 
 Ga 
 
 
 
 
 
 
 59-0 
 
 58-7 
 
 
 
 70 
 
 Ge 
 
 
 
 
 
 
 
 
 
 
 74 
 
 As 
 
 
 
 
 
 
 
 
 
 
 75 
 
 Se 
 
 
 
 
 
 
 
 
 
 
 79-1 
 
 Br 
 
 
 
 
 Rb 
 
 
 
 
 
 
 79-96 
 
 
 Kr 
 
 
 85-4 
 
 Sr 
 
 
 
 
 
 
 
 81-5 
 
 
 
 87-6 
 
 Y 
 
 
 
 
 
 
 
 
 
 
 89 
 
 Zr 
 
 
 
 
 
 
 
 
 
 
 90-6 
 
 Nb 
 
 
 
 
 
 
 
 
 
 
 94 
 
 Mo 
 
 
 
 
 
 
 
 
 
 
 96-0 
 
 t 
 
 
 
 
 Ag 
 107-95 
 
 Cd 
 
 
 
 
 
 99 
 
 Ru 
 
 101-7 
 
 Rh 
 103-0 
 
 Pd 
 
 106 
 
 
 112 
 
 In 
 
 
 
 
 
 
 
 
 
 
 144 
 
 Sn 
 
 
 
 
 
 
 
 
 
 
 119-0 
 
 Sb 
 
 
 
 
 
 
 
 
 
 
 
 120 
 
 Te 
 
 
 
 
 
 
 
 
 
 
 127-6 
 
 I 
 
 
 
 
 Cs 
 
 
 
 
 
 
 126-85 
 
 
 X 
 
 
 133-0 
 
 Ba 
 
 
 
 
 
 
 
 1SS 
 
 
 
 137-16 
 
 La 
 
 
 
 
 
 
 
 
 
 
 138 
 
 Ce 
 
 
 
 
 
 
 
 
 
 
 140 
 
 Prd 
 
 
 
 
 
 
 
 
 
 
 141 
 
 Nd 
 
 
 
 
 
 
 
 
 
 
 143-5 
 
 V 
 
 
 
 
 V 
 
 
 
 
 
 
 152 
 
 
 
 
 165 
 
 9 
 
 
 
 
 
 
 
 
 
 
 170 
 
 Yb 
 
 
 
 
 
 
 
 
 
 
 173 
 
 9 
 
 
 
 
 
 
 
 
 
 
 176 
 
 Ta 
 
 
 
 
 
 
 
 
 
 
 183 
 
 W 
 
 
 
 
 
 
 
 
 
 
 184 
 
 1 
 
 
 
 
 An 
 
 
 
 
 
 
 185 
 
 Os 
 
 Ir 
 
 Pt 
 
 197-2 
 
 Hg 
 
 
 
 
 
 
 191 
 
 193 
 
 195-2 
 
 
 200-3 
 
 Tl 
 
 
 
 
 
 
 
 
 
 
 204.1 
 
 Pb 
 
 
 
 
 
 
 
 
 
 
 206-9 
 
 Bi 
 
 
 
 
 
 
 
 
 
 
 208-5 
 
 ? 
 
 
 
 
 
 
 
 
 
 
 210 
 
 ? 
 
 
 
 
 ? 
 
 
 
 
 
 
 211 
 
 
 \v "V 
 
 
 222 
 
 Ra 
 
 
 
 , 
 
 
 
 
 o. v 
 
 
 
 226 
 
 ^ 
 
 
 
 
 
 
 i* 
 
 
 
 
 230 
 
 Th 
 
 
 
 
 
 
 
 
 
 
 232 
 
 V 
 
 
 
 
 
 
 
 
 
 
 234 
 
 U 
 
 
 
 
 
 
 
 
 
 
 240 
 
 ? 
 
 
 
 
 
 
 
 
 
 
 242 
 
 
 
 
PERIODIC ARRANGEMENT OF ELEMENTS 165 
 
 uranium ; but there are certain gaps unfilled, denoted by 
 the sign ?, which, it is believed, represent the places of 
 still undiscovered elements. Indeed, Meyer's original 
 diagram contained a larger number of these; and Men- 
 deleeff, averaging the properties of the elements surround- 
 ing such gaps, prophesied the discovery of scandium, 
 gallium, and germanium, made at a much later date by 
 Cleve, by Lecoq de Boisbaudran, and by Winckler. 
 
 There are many other ways of representing these rela- 
 tions; but except perhaps in convenience (and questionably 
 even in that), they present no particular advantage, and 
 convey no new knowledge. Only one point must be 
 emphasised. The elements, as arranged above, divide 
 themselves into two 'periods' long periods and short 
 periods. Thus the seventh member after lithium, sodium, 
 is in its character very like lithium; and, again, potassium, 
 the seventh after sodium, presents strong analogies with 
 the two elements named ; but it is then necessary to pass 
 over fifteen elements before rubidium is reached, which 
 again closely resembles lithium, sodium, and potassium ; 
 and csBsium, the seventeenth element after rubidium, forms 
 the first term of another long period. Copper, silver, and 
 gold are also separated by long periods ; and so with the 
 elements in the other columns. To distinguish these in 
 the table, the symbols of the elements in the middle of 
 the long periods are printed towards the left, and those at 
 the beginning towards the right, of the figures denoting 
 the atomic weights. 
 
 One other point requires mention. Several instances 
 occur in which the elements appear to occupy a reversed 
 position. Thus, nickel, with the atomic weight 587, 
 follows cobalt, to which a higher atomic weight is ascribed; 
 tellurium precedes, instead of following iodine ; and it will 
 be seen that argon precedes potassium. The differences 
 between the various consecutive atomic weights are 
 
166 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 irregular, and vary between fairly wide limits ; and it is 
 quite probable that these differences may occasionally be 
 negative. 
 
 In 1894 a new constituent of the atmosphere, which 
 was named ' argon/ was discovered by Lord Rayleigh and 
 Ramsay; this was followed in 1895 by the discovery by 
 Ramsay of helium in certain minerals. This gas gives a 
 spectrum in which a brilliant yellow line is conspicuous. 
 So long ago as 1868 this line had been observed in the 
 solar spectrum by Jansen; it was attributed by Frank- 
 land and Lockyer to the presence of a new element in 
 the sun, and they named the then unknown element 
 ' helium.' These discoveries were followed by that of three 
 other gaseous elements in atmospheric air, by Ramsay and 
 Travers in 1898; thus five elements were added to the 
 list. All these elements are distinguished by their inert- 
 ness, for none of them forms compounds with other 
 elements. 
 
 The Roman figures at the head of the columns of the 
 periodic table have a certain significance. They show the 
 maximum number of atoms of hydrogen which the ele- 
 ments in each column can combine with or replace, or, as 
 it is termed, their 'valency.' Thus an atom of lithium 
 combines with one atom of hydrogen ; it can also replace 
 one atom, as when it forms lithium hydroxide, LiOH, in 
 which it has replaced one atom of hydrogen in water, 
 H 2 0. So also magnesium can replace two atoms of 
 hydrogen, for it forms the hydroxide Mg(OH) 2 . Boron 
 combines with three atoms of hydrogen; carbon with 
 four; phosphorus, although it can combine with only 
 three atoms of hydrogen, can replace five ; for it forms a 
 chloride PC1 5 , in which it has replaced the five atoms of 
 hydrogen in five molecules of hydrogen chloride, 5HC1. 
 Sulphur forms a hexafluoride, and iodine a pentafluoride, 
 in which they replace six and five atoms of hydrogen 
 
PERIODIC ARRANGEMENT OF ELEMENTS 167 
 
 respectively, in 6HF, and in 5HF. Only one of the ele- 
 ments of the eighth group appears to be able to replace 
 eight atoms of hydrogen, namely, osmium ; it forms a 
 tetroxide, Os0 4 , thus replacing the eight atoms of hydrogen 
 in four molecules of water, 4H 2 0. But the new gaseous 
 elements of the atmosphere form no compounds, and have 
 no valency, as the power of replacing or combining with 
 hydrogen is termed. They thus form a column by them- 
 selves; and it was interesting to ascertain whether their 
 atomic weights would form a series like those in the other 
 columns. In this case, the atomic weight could not be 
 determined by the usual process of determining the ratio 
 in which the elements combine with hydrogen ; hence a 
 different method was adopted, depending on the known 
 fact that equal numbers of molecules of gases occupy 
 equal volumes under the same conditions of temperature 
 and pressure ; and making use of an argument relating to 
 the number of atoms in such molecules. The atomic 
 weights were : 
 
 Helium 
 
 4 
 
 Neon 
 20 
 
 Argon 
 39-9 
 
 Krypton 
 81-5 
 
 Xenon 
 128 
 
 These numbers, as will be seen on reference to the table, 
 fit in the eighth column ; the symbols and atomic weights 
 of these gases are printed in italics. They form the initial 
 members of the first and second short series, and of the 
 first, second, and third long series. 
 
 Some doubt exists as to the place to be assigned to 
 hydrogen, the element with lowest atomic weight. Both 
 Mendeleeff and Meyer shirked placing it. It may be that 
 it should be placed at the head of the fluorine column ; 
 but there are equally good, or perhaps better, reasons for 
 believing that it is the first member of the lithium 
 column. 
 
168 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Many attempts have been made to devise some mathe- 
 matical relation between these atomic weights. So long 
 as there was reason to doubt the accuracy of the experi- 
 ments by means of which the atomic weights have been 
 determined, some such relation as the following had 
 considerable probability in its favour : Taking the 
 differences between the atomic weights of the elements 
 in the first column, lithium, sodium, potassium, rubidium, 
 and caesium, they are 
 
 K-Na = 39-23 = 16; 
 
 Rb-K = 85-39 = 46 = (3xl6) nearly; 
 
 Cs-Rb = 133-85 = 48 = (3xl6). 
 
 The differences are 16, 16, 3x16, and 3x16. Now 
 there are compounds of carbon and hydrogen which 
 possess the formulae, CH 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 , C 5 H 12 , C 6 H 14 , 
 etc. ; and as the atomic weight of carbon is 12, and that of 
 hydrogen 1, the sum of the atomic weights, or, as they are 
 called, the molecular weights, are respectively 16, 30, 44, 
 58, 72, 86, etc., with a common difference of 14. We see, 
 therefore, that a set of compounds may so differ in mole- 
 cular weight as to present a regular series, with a common 
 difference. Nothing was more likely, then, than that 
 sodium should be regarded as a compound of one atom of 
 lithium with one atom of an unknown element of atomic 
 weight 16, or with two atoms of an unknown element of 
 atomic weight 8 ; while potassium might be looked upon 
 as a compound of an atom of lithium, with four atoms of 
 the element of atomic weight 8 ; and so on. But, unfor- 
 tunately for this simple theory, the differences between 
 the atomic weights of the elements are not exactly equal. 
 Instead of 16, the real difference between the atomic 
 weights of lithium and sodium is 16 '02; between potassium 
 
PERIODIC ARRANGEMENT OF ELEMENTS 169 
 
 and sodium, 16'09; and so on. In other groups the 
 divergences are still more striking. 
 
 The cause of this Jrregularity has, therefore, to be 
 sought. In seeking for a clue, the first question is : Are 
 the atomic weights invariable ? A further question is : Is 
 weight invariable ? Does a body always possess the same 
 weight under all conditions ? For example, would the 
 weight of a body remain the same if it were to be weighed 
 at different temperatures? Or, if electrically charged, 
 would its weight remain unaltered ? 
 
 It is a very difficult problem to weigh an object at a 
 high temperature. If the balance, as is usual, contains 
 air, convection currents are produced by the ascent of air 
 heated by the warm body, and the body apparently weighs 
 too little. If the whole balance were uniformly heated, 
 the weights would be at the same temperature as the 
 substance weighed ; and it is to be presumed that both 
 they and the substance would alter in weight equally, and 
 still remain in counterpoise. And if the balance case be 
 pumped empty of air, as was done by Crookes in deter- 
 mining the atomic weight of thallium, other phenomena 
 intervene, which, however interesting in themselves (they 
 led Crookes to the invention of the radiometer), are very 
 disconcerting ; for attractions and repulsions, which com- 
 pletely disturb equilibrium, are produced by the slightest 
 variations of temperature. However, some curious calcula- 
 tions have been made by Hicks in dealing with Baily's 
 experiments on the attraction of leaden balls by masses 
 of lead experiments which afford data for calculating the 
 density of the earth. At a high temperature the attraction 
 appeared to be less than at a low one ; and as the attrac- 
 tion of the earth is the cause of weight, supposing these 
 experiments to be correct, and the deductions legitimate, 
 it would follow that weight is altered by temperature. 
 The subject is well worthy of further experiment. 
 
170 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 Again, interesting experiments have been made by 
 Landolt as regards constancy of weight. Having sealed 
 up in an inverted U-tube two substances capable of acting 
 on each other, such as silver nitrate and sodium chloride, 
 each substance in solution occupying one limb of the 
 tube, he weighed the tube with the utmost accuracy ; the 
 possible error might be one part in a million. On inverting 
 the tube, the two solutions mixed, and the reaction took 
 place. It was again weighed. For long, Landolt supposed 
 that he had detected small changes in weight, sometimes 
 negative, sometimes positive; but he was able to trace 
 these changes to the porous nature of glass. On employ- 
 ing tubes made of fused quartz, no change of weight could 
 be detected after the reaction was over. Apparently, 
 therefore, no change of weight takes place as the result of 
 a chemical reaction, provided nothing leaves or enters the 
 vessel in which the reaction goes on. 
 
 A very ingenious experiment of Joly's deserves mention. 
 It was designed to try whether any change of mass occurs 
 on mixing two reacting bodies, and the disposition of the 
 apparatus was somewhat like that devised by Landolt. 
 But instead of utilising the attraction of the earth in order 
 to estimate whether the mass had changed or not, the 
 inertia of the substances and of their mixture was deter- 
 mined. The vessel containing the substances to be mixed 
 was suspended to the arm of a torsion-balance, the arm of 
 which was at right angles to the direction of motion of the 
 earth, which is known to be at the rate of about 30 miles 
 a second through space. If matter had been created 
 during the chemical change, then the created matter 
 would not partake of the earth's velocity, and a retarda- 
 tion, made manifest by the rotation of the arms of the 
 torsion-balance in one direction, would have been observed ; 
 and. if, on the other hand, matter had been destroyed, an 
 acceleration would have shown itself. The experiments 
 
PERIODIC ARRANGEMENT OF ELEMENTS 171 
 
 were entirely negative ; hence it may be concluded, con- 
 firmatory of the experiments of Landolt, that no change 
 in mass is produced by a chemical reaction. A variation 
 in weight or in inertia has not been observed. 
 
 There is one curious discrepancy which still remains 
 unexplained. The density of nitrogen gas has been very 
 accurately determined by two very competent observers 
 Lord Rayleigh and Leduc. They both agree in their 
 results to one part in 10,000. Now it is known, for reasons 
 into which we cannot enter here, that the molecules of 
 both nitrogen and oxygen consist each of two atoms ; and 
 as it is also certain that equal volumes of gases contain 
 nearly equal numbers of molecules, when measured under 
 similar conditions of temperature and pressure, the rela- 
 tive weights of these gases correspond to the relative 
 weights of the atoms. The word ' nearly ' has been used ; 
 for a slight correction must be introduced in order to 
 secure exact correspondence. Hence the atomic weight 
 of nitrogen, referred to that of oxygen taken as 16, as is 
 now customary, must be 14r008, since that is the density of 
 nitrogen referred to oxygen as 16, after the necessary cor- 
 rection has been made. But this number does not corre- 
 spond with the atomic weight of nitrogen obtained by the 
 celebrated chemist Stas, as the result of the analysis of such 
 compounds as potassium nitrate, when he determined the 
 ratio between the quantities of nitrogen and oxygen in 
 the molecule KN0 3 . Both he and, quite recently, one 
 of the most skilful of analysts, to whom we owe in recent 
 years many exact determinations of atomic weights, 
 Theodore Richards, agreed in ascribing the number 14'04 
 to nitrogen as its atomic weight. The difference does not 
 appear very great ; but yet it amounts to one part in 370 : 
 and the error of experiment is not likely to be greater 
 than one part in 10,000. This discrepancy is one of. the 
 most curious of chemical facts, and it would well repay 
 
172 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 further investigation. It may be added that the deter- 
 mination by Gray of the density of nitric oxide, a com- 
 pound containing one atom of nitrogen in combination 
 with one atom of oxygen, entirely corroborates the results 
 of Lord Rayleigh and Leduc. Experiments are now in 
 progress to combine a weighed quantity of nitric oxide 
 with oxygen, so as to cause it to take up one other atom 
 of oxygen, and to find the increase in weight ; and also 
 to remove from it the atom of oxygen, and to find the 
 weight of the oxygen removed ; we may, therefore, hope 
 for some explanation of the above discrepancy at no dis- 
 tant date. 1 
 
 The writer of this article was so much impressed by the 
 consideration of this discrepancy, that some years ago, in 
 conjunction with Miss Aston, an attempt was made to 
 find whether the fact of a compound having been formed 
 with absorption, instead of, as is commoner, with evolu- 
 tion of heat, had any influence on the proportions of the 
 elements which it contained. For this purpose the salts 
 of a curious acid derivative of nitrogen named hydrazoic 
 acid, HN 3 , were analysed ; but there is reason to distrust 
 the results, for it is possible that decomposition occurred 
 during the preparation to some small extent, and so may 
 not have led to trustworthy conclusions. But such as 
 they were, they were in favour of the supposition that the 
 atomic weight of nitrogen in such compounds is less than 
 in those formed with evolution of heat, like the nitre 
 analysed by Stas and by Richards. 
 
 An entirely new light has been thrown on the numerical 
 relations of the atoms by the remarkable discovery of 
 radium by the Curies, and by the discovery by Rutherford 
 and Soddy, that what are termed the ' rays ' from its salts, 
 
 1 Such investigations have since been carried out by Dr. R. Gray and 
 by Professor Philippe Guye, with the result that the true atomic weight 
 of nitrogen has been fixed as 14*01. 
 
Y I 
 
 OF 
 
 PERIODIC ARRANGEMENT OF ELEMENTS 173 
 
 as well as from those, of thorium, are produced by gases 
 resembling in their inertness the gases of the argon group. 
 These gases, moreover, have the extraordinary property 
 that they are transient, although they change in very 
 different intervals of time. Whereas the gas from thorium 
 is half gone in about a minute (that is, has changed to 
 the extent of one-half into some other substance or sub- 
 stances), that from radium requires about four days before 
 it has undergone half the change of which it is capable. 
 A third gas has been obtained from a radio-active element 
 to which the name ' actinium ' has been given by its dis- 
 coverer, Debierne; this gas has an extraordinarily short 
 life, for the total duration of its existence is only a few 
 seconds. The spectrum of the gas from radium has been 
 mapped by Ramsay and Collie ; the amount of gas pro- 
 duced from a known weight of radium bromide has been 
 measured by Ramsay and Soddy; and they, too, proved 
 that one of its products of decomposition is the lightest 
 gas of the argon group, helium. At first, the spectrum of 
 the emanation from radium shows none of the character- 
 istic lines of helium ; but in the course of a few days the 
 helium spectrum appears in full brilliancy. Here, evi- 
 dently, is a case of the transformation of one element into 
 another ; no doubt there are other products than helium, 
 but what they are remains for the present unknown. If 
 they were elements like iron, for example, there are at 
 present no known means delicate enough to detect the 
 extremely minute amount which would be produced. 
 These gases from radium, thorium, and actinium are self- 
 luminous, and shine brilliantly in the dark ; and they also 
 possess the power of altering air and other gases with 
 which they are mixed, so that they acquire the property 
 of discharging an electrified body; the air is said to be 
 ' ionised.' But a still more remarkable property is their 
 giving off heat during their change into other elements, 
 
174 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 the amount of heat being enormous when their extremely 
 small quantity is considered. Thus the radium emana- 
 tion (the name applied to the gas which is continuously 
 evolved from salts of radium), during its decomposition 
 gives off no less than three million times the heat which 
 would be evolved during the explosion of an equal volume 
 of a mixture of oxygen and hydrogen in the proportion 
 requisite to form water. Now if radium is disappearing, 
 it must be continually in process of formation, else there 
 would be none on the surface of the earth ; it would all 
 have disappeared and have been changed into other 
 bodies during the lapse of time since the minerals con- 
 taining it were formed. As radium is always associated 
 with uranium, it appears not unreasonable to suppose that 
 uranium, too, which is a radio-active element, is slowly 
 changing into radium ; and there appears to be definite 
 ground for the surmise that polonium, the first of the 
 radio-active elements, also discovered by Madame Curie, 
 which has a half-life period of about one year, is a product 
 of the decomposition of radium, with which it is always 
 associated. It may be mentioned, too, that all minerals 
 containing uranium contain more or less helium. 
 
 It will be noticed, on referring to the periodic table, 
 that all the radio-active elements, that is, all those which 
 are undergoing change of the nature described, have very 
 high atomic weights. That of uranium is 240; that of 
 thorium, 232 ; and that of radium, 226. Now it is a com- 
 monplace of the organic chemist that it is not possible to 
 build up compounds of carbon and hydrogen of unlimited 
 complexity; indeed, it is doubtful if any compound has 
 been prepared containing more than 100 atoms of carbon. 
 Attempts to prepare them lead to failure, owing to their 
 decomposing at the ordinary temperature into compounds 
 containing a smaller number of atoms. And it is pro- 
 bable that more complex hydrocarbons, as such com- 
 
PERIODIC ARRANGEMENT OF ELEMENTS 175 
 
 pounds are termed, would, if they could exist, decompose 
 with evolution of heat. Such a decomposition appears to 
 present analogy with the change which an element like 
 radium is undergoing. It is in process of change into 
 other elements of lower atomic weight ; and in changing, 
 it evolves heat, in amount enormously greater than that 
 produced by any change of a compound into a mixture of 
 simpler compounds. But the matter is complicated by 
 another phenomenon that of discharging with almost 
 inconceivable velocity particles which appear, according 
 to J. J. Thomson, to be identical with negative electricity. 
 These ' corpuscles/ as they have been termed, embed them- 
 selves in the vessel in which the radio-active body is 
 confined ; and, owing to their extreme minuteness, they 
 may even pass through the walls of the containing vessel. 
 Indeed the opposition of their passage has been shown to 
 depend merely on the density of the matter of which the 
 confining walls are composed ; gold, which is denser than 
 lead, stops their passage better than lead; for a similar 
 reason lead is better than iron, iron better than glass, and 
 so on. Thomson has calculated that the mass of one such 
 particle is approximately one-thousandth of that of an 
 atom of hydrogen. 
 
 This new chemistry is just at its commencement. It 
 dates from 1896, when Becquerel showed that compounds 
 of uranium evolved some sort of radiation which would 
 impress a photographic plate. It is still too early to 
 formulate any definite statement relating to its connection 
 with the irregularity in the numerical sequence of the 
 atomic weights ; yet it may be permissible to speculate, 
 aided by the recent discoveries. When two elements 
 combine, heat is generally evolved ; now heat is only one 
 form of energy, and the combination of elements may be 
 so carried out as to be accompanied by other kinds of 
 energy for instance, by the production of an electric. 
 
176 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 current. Conversely, when a compound is resolved into 
 its elements, it is generally necessary to impart energy to 
 it ; and the element may, therefore, be said to ' contain ' 
 more energy than its compounds. Now, as Ostwald has 
 pointed out in his 'Faraday' lecture, the progress of 
 discovery has kept pace with the amount of energy with 
 which it was possible at the time to load a compound; 
 and he cited the discovery of the metals of the alkalies, 
 sodium and potassium, by Davy. It was because Davy 
 had at his disposal the powerful battery of the Royal 
 Institution, that he was able to convey enough energy 
 into caustic potash to isolate from it potassium, hydrogen, 
 and oxygen. If we assume that radium, as may be 
 possible, is produced by a spontaneous change in uranium ; 
 and if we also assume that radium contains more energy 
 than uranium ; then as such a spontaneous change must 
 be accompanied, on the whole, by a loss of energy, there 
 must be formed other bodies from the uranium which 
 contain less energy than it does. Such a substance may 
 be iron, which is generally found in company with uranium. 
 If we could concentrate energy into iron, it might be 
 possible to convert it into uranium. 
 
 But there is another side to this question. The nature 
 of the energy required appears to be electric in character. 
 Now it is almost certain that negative electricity is a 
 particular form of matter; and positive electricity is 
 matter deprived of negative electricity that is, minus this 
 electric matter. The addition of matter in any form would, 
 according to all experience, increase mass ; it would also in- 
 crease weight. It is, therefore, conceivable that an element 
 may consist of a compound of two or more elements of 
 lower atomic weight, plus a certain quantity of negative 
 electricity. This might account for the approximate 
 numerical relations which subsist between the atomic 
 weights of the nearly related elements ; and also for the fact 
 
PERIODIC ARRANGEMENT OF ELEMENTS 177 
 
 that the relation is not an exact one, but only approximate ; 
 for the difference between the actual atomic weight, and 
 that which would follow if one element were a compound 
 of other elements of lower atomic weights, would be caused 
 by the addition of a certain number of electric atoms to 
 the molecule. 
 
 It must be confessed, however, that the basis for specu- 
 lations like these is a slender one ; the sole ground is the 
 undoubted fact that radium produces an emanation 
 which spontaneously changes into helium ; and also that, 
 in doing so, the emanation parts with a large number 
 of corpuscles carrying negative charges. Nevertheless, 
 enough is known to prove that there is a wide field for 
 experiment, and that the harvest will be a rich one; 
 further, the reapers' task will be one of extraordinary 
 interest. 
 
RADIUM AND ITS PRODUCTS 
 
 CHEMISTRY and physics are experimental sciences; and 
 those who are engaged in attempting to enlarge the 
 boundaries of science by experiment are generally un- 
 willing to publish speculations ; for they have learned, by 
 long experience, that it is unsafe to anticipate events. It 
 is true they must make certain theories and hypotheses. 
 They must form some kind of mental picture of the 
 relations between the phenomena which they are trying 
 to investigate, else their experiments would be made at 
 random and without connection. Progress is made by 
 trial and failure; the failures are generally a hundred 
 times more numerous than the successes; yet they 
 are usually left unchronicled. The reason is that the 
 investigator feels that even though he has failed in 
 achieving an expected result, some other more fortunate 
 experimenter may succeed, and it would be unwise to 
 discourage his attempts. 
 
 In framing his suppositions, the investigator has a 
 choice of five kinds; they have been classified by Dr. 
 Johnstone Stoney. ' A theory is a supposition which we 
 hope to be true, a hypothesis is a supposition which we 
 expect to be useful ; fictions belong to the realm of art ; if 
 made to intrude elsewhere, they become either make- 
 believes or mistakes/ Now the ' man in the street/ when 
 he thinks of science at all, hopes for a theory ; whereas 
 the investigator is generally contented with a hypothesis, 
 and it is only after forming and rejecting numerous hypo- 
 
 179 
 
180 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 theses that he ventures to construct a theory. He has a 
 rooted horror of fiction in the wrong place, and he dreads 
 lest his hypothesis should turn out to be misplaced 
 fiction. 
 
 I have thought it better to begin by these somewhat 
 abtruse remarks, in order to place what I propose to 
 discuss on a true basis. It is to be understood that any 
 suppositions which I shall make use of are of the nature 
 of hypotheses, devised solely because they may prove 
 useful. Events are not yet ripe for a theory. 
 
 It will be remembered that Professor Rutherford and 
 Mr. Soddy announced a ' view ' that certain elements 
 which possess the power of discharging an electroscope, 
 and which are therefore called ' radioactive/ are suffering 
 disintegration that is, they are splitting up into other 
 elements, only one of which has as yet been identified. 
 Three of these elements, namely, radium, thorium, and 
 actinium, early in the process of disintegration give off an 
 ' emanation,' or supposed gas ; the proof of the gaseous nature 
 of these emanations is that they can be confined by glass 
 or metal, like gases, and that they can be liquefied or 
 solidified when cooled to a sufficiently low temperature. 
 It is necessary to pay attention to this peculiarity; for 
 these radioactive elements, and two others, uranium and 
 polonium, also give off' so-called /3-rays, which penetrate 
 glass and metal, and which are believed from the dis- 
 coveries of Professor J. J. Thomson and others to be 
 identical with negative electricity. 
 
 Now Rutherford and Soddy, reasoning on the premises 
 that radium was always found associated with uranium 
 and thorium, and also that the ores of these metals, 
 pitchblende and thorite, had been found to contain the 
 gas helium, made the bold suggestion, ' The speculation 
 naturally arises whether the presence of helium in minerals 
 and its invariable association with thorium and uranium 
 
RADIUM AND ITS PRODUCTS 181 
 
 may not be connected with their radioactivity.' Besides 
 the premises already mentioned, they had evidence of 
 the probable mass of the ' a-particles,' which appeared to 
 be about twice that of an atom of hydrogen. Now 
 helium is the lightest gas next to hydrogen; and its 
 atoms are four times as heavy as atoms of hydrogen. It 
 was, therefore, a striking confirmation of the accuracy of 
 this view when Ramsay and Soddy discovered that helium 
 can actually be obtained from radium. 
 
 Before giving an account of that discovery, a short 
 description of the nature and properties of helium may 
 not be out of place. When light passes through a prism, 
 it is refracted or bent ; and Newton discovered that white 
 light, such as is emitted from the sun or the stars, after 
 passing through a prism, gives a spectrum consisting of 
 coloured images of the hole in the window-shutter through 
 which the sunlight fell on his prism. Fraunhofer, a 
 Berlin optician, conceived the idea of causing the light to 
 pass through a narrow slit, instead of a round hole ; and 
 the spectrum then consisted of a number of images of the 
 narrow slit, instead of the round hole. He was struck by 
 one peculiarity shown by sunlight when thus examined, 
 namely, that the coloured band, rainbowlike, and exhibit- 
 ing a regular gradation of colour from red at the one end, 
 through orange, yellow, green, and blue, to violet at the 
 other end, was interspersed by very numerous thin black 
 lines. The nature of these lines was discovered by 
 Kirchoff. The light emitted by a white-hot body shows 
 a continuous spectrum ; but if such white light be passed 
 through the vapours of a metal, such as sodium, a portion 
 is absorbed. For example, glowing sodium gas shows two 
 yellow lines, very close together ; but if this light is passed 
 through the vapour of sodium, these lines are extinguished 
 if the correct amount of vapour be interposed. Now it 
 was found that the position of the two dark lines in the 
 
182 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 sun's spectrum, discovered by Fraunhofer, is identical 
 with that of the two yellow lines visible in the spectrum 
 of glowing sodium vapour ; and Kirchoff concluded that 
 this coincidence furnished a proof of the presence of 
 sodium in the sun. Fraunhofer had named these lines 
 D : and D 2 . Similar conclusions were drawn from obser- 
 vations of the coincidence of other black solar lines with 
 those of elements found on the earth ; and the presence 
 of iron, lead, copper, and a host of elements in the sun 
 was proved. 
 
 In 1868 a total eclipse of the sun took place; an 
 expedition was sent to India, from which a good view was 
 to be obtained. Monsieur Janssen, the distinguished 
 French astronomer, observed a yellow line, not a dark, but 
 a bright one, in the light which reached the earth from 
 the edge or ' limb ' of the sun, and which proceeded from 
 its coloured atmosphere or chromosphere. It was for 
 some time suspected that this line, which was almost 
 identical in position with the yellow lines of sodium, D l 
 and D 2 , and which Janssen named D 3 , was due to 
 hydrogen. But ordinary hydrogen had never been found 
 to show such a line ; and after Sir Edward Frankland and 
 Sir Norman Lockyer had convinced themselves by 
 numerous experiments that D 3 had nothing to do with 
 hydrogen, they ascribed it to a new element, the exist- 
 ence of which on the sun they regarded as probable ; 
 and for convenience, they named this undiscovered 
 element 'helium/ from the Greek word for the sun, 
 
 It was not until the year 1895 that helium was found 
 on the earth. After the discovery of argon in 1894, 
 Ramsay repeated some experiments which had previously 
 been made by Dr. Hillebrand, of the United States Geo- 
 logical Survey. Hillebrand had found that certain 
 minerals, especially those containing the somewhat rare 
 
RADIUM AND ITS PRODUCTS 183 
 
 elements uranium and thorium, when heated, or when 
 treated with acids, gave off a gas which he took for 
 nitrogen. But the discovery of argon had taught Ramsay 
 how to deal with such a gas. He examined it in the hope 
 that it might lead to the discovery of a compound of 
 argon ; but its spectrum turned out to be identical with 
 that of solar helium, and terrestrial helium was discovered. 
 It proved to be a very light gas, only twice as heavy as 
 hydrogen, the lightest substance known ; its spectrum con- 
 sists chiefly of nine very brilliant lines, of which D 3 is the 
 most brilliant ; it has never been condensed to the liquid 
 state, and is the only gas of which that can now be said 
 (for hydrogen has been liquefied within the last few years 1 ), 
 and, like argon, it has not been induced to form any 
 chemical compound. That it is an element is shown by 
 the relation of its atomic weight, 4, to that of other 
 elements, as well as by certain of its properties, the most 
 important of which is the ratio between its specific heat 
 at constant volume and constant pressure ; but to explain 
 the bearing of this property on the reasoning which proves 
 it to be an element would be foreign to the subject of this 
 article. 
 
 This then was the elementary substance that Ruther- 
 ford and Soddy suspected to be one of the decomposition 
 products of radium. The word ' decomposition,' however, 
 implies the disruption of a compound, and the change 
 which takes place when radium produces helium is of 
 such a striking nature that it is perhaps preferable to use 
 the term c disintegration.' 
 
 Having procured fifty milligrammes (about three- 
 quarters of a grain) of radium bromide, Ramsay and 
 Soddy placed the greyish-brown crystalline powder in a 
 small glass bulb about an inch in diameter. This bulb 
 was connected by means of a capillary tube with another 
 
 1 It has since been liquefied by Kammerlingh Onnes of Leiden. 
 
184 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 bulb of about the same size ; on each side of the second 
 bulb there was a stop-cock, as shown in the sketch. To 
 begin with, the bulb A was pumped empty of air; it 
 contained the dry bromide of radium. The 
 stop-cock B was then shut. Next, some 
 water was placed in bulb (7, and it too was 
 pumped free from air, and the stop -cock D 
 was closed. B was then opened, so that 
 the water in C flowed into A , and dissolved 
 up the bromide of radium. As it was 
 dissolving, gas bubbles were evolved with 
 effervescence, and that gas collected in the 
 two bulbs, A and B. The sketch shows the 
 state of matters after the water had been 
 added and the gas evolved. The apparatus 
 was then permanently sealed on to a tube 
 connected with a mercury-pump, so con- 
 trived that gas could be collected. The stop- 
 cocks having been opened, the gas passed 
 into the pump, and was received in a small 
 test-tube. From the test-tube it was passed into a reservoir, 
 where it was mixed with pure oxygen, and electric sparks 
 were then passed through it for some hours, a little caustic 
 soda being present. This process has the result of causing 
 all gases except those like argon to combine, and they are 
 therefore removed. It was easy to withdraw oxygen by 
 heating a little phosphorus in the gas ; and it was then 
 passed into a small narrow glass tube, which had a platinum 
 wire sealed in at each end a so-called Plticker's vacuum- 
 tube. On passing an electric discharge from a Ruhmkorff 
 induction-coil through the gas in the tube, the well-known 
 spectrum of helium was seen. 
 
 Thus helium was proved to be contained in radium 
 bromide which had stood for some time. The specimen 
 used was said to be about three months old, and the 
 
 EXTRACTION OP 
 
 GASES FROM 
 RADIUM BROMIDE 
 
RADIUM AND ITS PRODUCTS 185 
 
 helium had accumulated. But whence came the helium ? 
 That was the next question to be settled. 
 
 A solution of radium bromide gives off gas continuously. 
 That gas, on investigation, is found to be a mixture of 
 oxygen and hydrogen, the constituents of the water in 
 which the bromide is dissolved. It contains, however, a 
 small excess of hydrogen, which implies that some oxygen 
 has been absorbed, probably by the radium bromide, 
 although what becomes of that excess has not yet been 
 determined. 
 
 When an electric spark is passed through a mixture of 
 oxygen and hydrogen, an explosion takes place; the 
 gases combine, and water is formed. Any excess of 
 hydrogen is, however, unaffected. Now the gases evolved 
 from a solution of radium bromide make glass luminous in 
 the dark, and possess the power of discharging an electro- 
 scope, like radium bromide itself. Rutherford and Soddy 
 discovered that when this mixture of gases is led through 
 a tube shaped like a U, cooled to - 185 C. by dipping in 
 liquid air, the luminous gas condenses, and the gases 
 which pass on have nearly ceased to be luminous in 
 the dark, and no longer discharge an electroscope. To 
 such condensable gases Rutherford applied the term 
 ' emanation ' ; this one is known as the ' radium emana- 
 tion.' 
 
 The next question to be answered was : Is the helium 
 evolved from the radium bromide directly, or is it a pro- 
 duct of the emanation ? It was necessary, therefore, to 
 collect the emanation and to examine its spectrum. This 
 was managed, after many unsuccessful trials, by exploding 
 the mixture of oxygen and hydrogen containing the 
 emanation, allowing the remaining hydrogen to pass into 
 a tube containing a thin spiral of slightly oxidised copper 
 wire kept at a red heat by an electric current: the 
 hydrogen combined with the oxygen of the oxide of 
 
186 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 copper, and formed water. The apparatus was so arranged 
 that mercury could be allowed to enter the tube from 
 below, so as to sweep before it any remaining gas ; and 
 the water was removed from the gas by making it pass 
 through a tube filled with a suitable absorbing agent, 
 followed up by mercury. The gas finally entered a very 
 small spectrum-tube, entirely made of capillary tubing, 
 like the stem of a thermometer. On passing a discharge 
 from a coil through the spectrum- tube after the emanation 
 had been thus introduced, a spectrum was seen, consisting 
 of some bright green lines ; but it was extremely difficult 
 to prevent the presence of traces of carbon compounds, 
 and at this stage their spectrum was always seen. But 
 the D 3 line of helium was absent. After a couple of days, 
 however, a faint yellow hue began to appear, identical in 
 position with D 3 ; and as time went on, that line became 
 more distinct, and was followed by the other lines charac- 
 teristic of helium, until, after a week, the whole helium 
 spectrum was visible. It was thus proved that the radium 
 emanation spontaneously changes into helium. Of course 
 other substances might have been, and undoubtedly were, 
 formed ; but these it was not possible to detect. 
 
 The next problem was to measure the amount of 
 emanation, resulting from a given weight of radium, in a 
 given time. The method of procedure was similar to that 
 already described, except in one respect: the spiral of 
 oxidised copper wire was omitted, and the excess of 
 hydrogen, mixed with the emanation, was cooled in a small 
 bulb by help of liquid air. This condensed the emanation; 
 and the hydrogen, which of course is not liquefied at the 
 temperature of liquid air, was pumped away. On removal 
 of the liquid air, the emanation became gaseous, and it 
 was forced by means of mercury into a minute measuring 
 tube, like the very narrow stem of a thermometer. It 
 was thus possible to measure its volume. It is a well- 
 
RADIUM AND ITS PRODUCTS 187 
 
 known law that gases decrease in volume proportionally 
 to increase of pressure ; if the pressure is doubled, the 
 volume of the gas is halved, and so on. Now this was found 
 to be the case with the emanation ; hence the conclusion 
 that it is a gas, in the ordinary meaning of the word. 
 But it is a very unusual gas ; for not only is it luminous 
 in the dark, but it slowly contracts, day by day, until it 
 practically all disappears. It does not lose its luminosity, 
 however; what remains, day by day, is as luminous as 
 ever ; but its volume decreased, until after about twenty- 
 five days the gas had contracted to a mere luminous 
 point. What had become of the helium ? That was dis- 
 covered on heating the tube. It is well known that glass, 
 exposed to the radium emanation, turns purple, if it is 
 soda glass; brown, if it is potash glass. This is due to 
 the penetration of the glass by the electrons, which are 
 exceedingly minute particles, moving with enormous 
 velocity. When the emanation changes into helium, 
 the molecules of that gas are also shot off with enormous 
 velocity, although they move much more slowly than the 
 electrons. It is sufficient, however, to cause them to 
 penetrate the glass ; but on heating they are evolved, and 
 collect in the tube, and the volume of the helium can be 
 measured. It turned out to be three and a half times 
 that of the emanation. But as the emanation is probably 
 fifty times as heavy as hydrogen, all the emanation is 
 not accounted for by the volume of helium found; it is 
 almost certain that solid products are formed, which are 
 deposited on the glass, and which are radioactive. Up to 
 the present these products have not been investigated 
 chemically. 
 
 It was possible, knowing the volume of the emanation, 
 and knowing also the volume which the radium would 
 have occupied had it, too, been gaseous (for a simple rule 
 enables chemists to know the volume which a given 
 
188 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 weight of any element would occupy in the state of gas), 
 to calculate how long it would take for the radium to be 
 converted into emanation, supposing that to be its only 
 product. This gives for half of the radium to be decom- 
 posed about 1150 years. But there is a good deal of 
 conjecture about the calculation; for many unproved 
 assumptions have to be made. 
 
 A further experiment, conducted in a somewhat similar 
 manner, but with the utmost precaution to exclude every 
 trace of foreign gas, made it possible to measure the 
 position of the lines of the spectrum of the emanation. 
 In general it may be said that the spectrum has a similar 
 character to those of argon and helium ; it consists of a 
 number of bright lines, chiefly green, appearing distinctly 
 on a black background. It confirms the supposition, 
 made after examination of the chemical properties of the 
 emanation, that it is a gas belonging to the argon group, 
 with a very heavy atomic weight. Some of the lines of 
 the spectrum appear to be identical with lines observed in 
 the spectra of the stars ; and it may perhaps be inferred 
 that such heavenly bodies are rich in radium. 
 
 In the diagram on page 184, the bulb containing radium 
 bromide there shown was surrounded by a small glass 
 beaker, as a precautionary measure. As a matter of 
 fact, there were three such bulbs and three such beakers, 
 on the principle of not putting all one's eggs in 
 one basket. These beakers had never been in contact 
 with the radium bromide, nor with the emanation ; but 
 they had been bombarded for months by /3-rays, or 
 electrons, which are so minute, and move so rapidly, that 
 they penetrate thin glass with ease. It was found that 
 these beakers were radioactive ; and it is very remarkable 
 that after washing with water, the beakers lost their radio- 
 activity, which was transferred to the water. Evidently, 
 then, some radioactive matter had been produced by the 
 
RADIUM AND ITS PRODUCTS 189 
 
 influence of the /3-rays. On investigation, it was proved 
 that more than one substance had been produced. For 
 on bubbling air through the water, a radioactive gas 
 passed away along with the air ; it had the power of dis- 
 charging an electroscope, but its life lasted only a few 
 seconds. It was only while the current of air was passing 
 through the electroscope that the gold-leaves fell together; 
 on ceasing the current, the leaves remained practically 
 stationary. Now had radium emanation been introduced 
 into the electroscope, its effect would have lasted twenty- 
 eight days ; had the emanation from thorium been intro- 
 duced, it would have taken about a minute before it ceased 
 to cause the gold-leaves to fall in. There is an emanation, 
 however, that from actinium, which is very short-lived, 
 and it looks probable that one of the substances produced 
 from the /3-rays is actinium. But it is not the only one. 
 For the water with which the glass was washed gives a 
 radioactive residue after evaporation to dryness; and it 
 contains a substance which forms an insoluble chloride, 
 sulphide, and sulphate, though the hydroxide is soluble in 
 ammonia. Either, then, the /S-rays have so altered the 
 constituents of the glass that new radioactive elements are 
 formed ; or perhaps it is the air which surrounds the glass 
 which has yielded these new elements; or it may be, 
 though this appears less probable, that the /3-rays them- 
 selves, which are identical with electrons, or ' atoms ' of 
 negative electricity, have condensed to form matter. 
 
 Such are some of the results which have been obtained 
 in a chemical examination of the products of change of 
 radium. The work is merely begun, but it leads to a 
 hypothesis as regards the constitution of radium and 
 similar elements, which was first put forward by Ruther- 
 ford and Soddy. It is that atoms of elements of high 
 atomic weight, such as radium, uranium, thorium, and the 
 suspected elements polonium and actinium, are unstable ; 
 
190 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 that they undergo spontaneous change into other forms of 
 matter, themselves radioactive, and themselves unstable ; 
 and that finally elements are produced which, on account 
 of their non-radioactivity, are, as a rule, impossible to 
 recognise, for their minute amount precludes the applica- 
 tion of any ordinary test with success. The recognition of 
 helium, however, which is comparatively easy of detection, 
 lends great support to this hypothesis. 
 
 The natural question which suggests itself is : Are other 
 elements undergoing similar change? Can it be that 
 their rate of change is so slow that it cannot be detected ? 
 Professor J. J. Thomson has attempted to answer this 
 question, and he has found that many ordinary elements 
 are faintly radioactive ; but the answer is still incomplete, 
 for, first, radium is so enormously radioactive that the 
 merest trace of one of its salts in the salt of another 
 element would produce such radioactivity ; and, second, it 
 is not proved that radioactivity is an invariable accompani- 
 ment of such change ; or, again, it may be evolved so 
 slowly as to escape detection. A lump of coal, for 
 example, is slowly being oxidised by the oxygen of the 
 air; oxidation is attended by a rise of temperature, but 
 the most delicate thermometer would detect no difference 
 between the temperature of a lump of coal and that 
 of the surrounding air, for the rate of oxidation is so 
 slow. 
 
 Another question which arises is : Seeing that an element 
 like radium is changing into other substances, and that its 
 life is a comparatively short one, it must be in course of 
 formation, else its amount would be exhausted in several 
 thousand years. An attempt has been made by Soddy to 
 see if uranium salts, carefully purified from radium, have 
 reproduced radium after an interval of a year; but his 
 result was a negative one. Possibly some other form of 
 matter besides uranium contributes to the synthesis of 
 
RADIUM AND ITS PRODUCTS 191 
 
 radium, and further experiments in this direction will be 
 eagerly welcomed. 1 
 
 Lastly, the experiments of Ramsay and Cook, of 
 which an account has been given, on the action of the 
 /3-rays appear to foreshadow results of importance. 
 For while radium, during its spontaneous change, parts 
 with a relatively enormous amount of energy, largely 
 in the form of heat, it is a legitimate inference that 
 if the atoms of ordinary elements could be made to 
 absorb energy, they would undergo change of a con- 
 structive and not of a disruptive, nature. If, as looks 
 probable, the action of /3-rays, themselves the con- 
 veyers of enormous energy, on such matter as glass, 
 is to build up atoms which are radioactive, and con- 
 sequently of high atomic weight ; and if it be found that 
 the particular matter produced depends on the element 
 on which the /3-rays fall, and to which they impart their 
 energy : if these hypotheses are just, then the transmuta- 
 tion of elements no longer appears an idle dream. The 
 philosopher's stone will have been discovered, and it is 
 not beyond the bounds of possibility that it may lead to 
 that other goal of the philosophers of the dark ages the 
 elixir vitce. For the action of living cells is also dependent 
 on the nature and direction of the energy which they 
 contain; and who can say that it will be impossible to 
 control their action, when the means of imparting and 
 controlling energy shall have been investigated ? 
 
 1 There appears to be an intermediate product to which the name 
 ' ionium ' has been given by Boltwood, its discoverer. 
 
WHAT IS ELECTRICITY ? 
 
 AN old friend of mine, by profession a banker, who 
 spent a large portion of his life of eighty-nine years in 
 studying geology and astronomy, once put to me the 
 question : ' Whence comes the motive power of electricity ? 
 I can understand the motive power of steam, but not of 
 electricity. 5 
 
 This led me to think on the subject ; and although there 
 is not much new in my reply, it contains, nevertheless, one 
 novel point, which contributes, I think, to clearness of 
 thought. 
 
 The answer refers only to electricity generated by a 
 battery; not to a current made by means of a dynamo 
 machine. The answer to the question, What generates a 
 current in a dynamo ? must be left till a later oppor- 
 tunity. 
 
 The simplest form of a battery consists of a vessel 
 containing dilute hydrochloric acid, into which dip a 
 copper and zinc plate, connected by a wire. A current 
 flows through the wire ; its presence can be demonstrated 
 by a galvanometer, or by dipping the wire from the copper 
 plate and the wire from the zinc plate into a solution of 
 iodide of potassium; a brown stain begins to appear at 
 the end of the wire connected with the zinc plate ; it is 
 caused by the iodine being set free, which dissolves in the 
 liquid with a brown colour. 
 
 If it is desired to make the test more striking a little 
 starch may be added to the solution of iodide of potassium. 
 
194 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 The colour will then be blue, for iodine and starch give a 
 blue colour. Now why does the current pass ? 
 
 To explain this, let us consider what happens to a 
 lump of sugar lying at the bottom of a cup of water. 
 After a few minutes the sugar will melt, or, more cor- 
 rectly, dissolve in the water. But the water at the top 
 will not be sweet for a long time ; the sugar takes a good 
 many minutes before it spreads up into the water. Why ? 
 It is believed that sugar consists of minute invisible 
 particles called molecules ; and they are in motion. 
 
 Although we cannot see molecules move, we may 
 nevertheless make an experiment which will prove to us 
 that particles of matter, easily visible under a fairly 
 powerful microscope, are always in rapid motion. 
 
 An ordinary water-colour paint, rubbed with water, 
 gives particles of a convenient size ; gamboge is perhaps 
 the best colour to take. These particles are always 
 ' jigging' to and fro; their motion is not regular, but 
 spasmodic; and they spread, in virtue of that motion; 
 so that they move from one part of the water to 
 another. 
 
 So it is with the sugar molecules ; that they do spread 
 is proved by the water becoming sweet, even at the 
 surface. In fact the sugar particles try to move from 
 where they are to where they are not. If one felt inclined 
 to moralise on the subject, one might ask, Is not that 
 what we all try to do ? Is not an attempt at motion what 
 makes for progress of all kinds in the world ? 
 
 If such motion could be hindered, say by a screen which 
 would block the passage of the sugar molecules, while 
 allowing the water molecules to pass, the sugar molecules 
 would bombard the screen, giving it innumerable blows, 
 and these blows would make themselves evident as a kind 
 of pressure on the screen. 
 
 This pressure has been measured ; a partition has been 
 
WHAT IS ELECTRICITY? 195 
 
 found which allows the water to pass, while blocking the 
 way for sugar. It is as if gravel of two sizes were being 
 shaken on a sieve; the stones which pass through the 
 meshes do not press on the sieve, while those which are 
 stopped by the sieve may be recognised by their 
 pressure. 
 
 Substances other than sugar, too, can be stopped by the 
 same screen ; for example, tartaric acid can. And it has 
 been found that the pressure produced by equal numbers 
 of molecules or particles of sugar and of tartaric acid, 
 contained in equal volumes of water, is equal. 
 
 Common salt is a compound of a metal named sodium 
 and a yellow-green gas called chlorine. Each molecule or 
 particle of salt must therefore contain these two elements ; 
 that is, each particle must be made up of at least two 
 smaller particles, and these smaller particles are called 
 ' atoms/ If a spoonful of salt be placed at the bottom of 
 a glass of water, like the sugar, its particles will wander 
 through the water, so that, after some time, the water will 
 become salt all through. 
 
 Just as with sugar, it is possible to find a membrane 
 which will allow water to pass through it, while it stops 
 the passage of salt; and it is possible to measure the 
 pressure of molecules of salt on the membrane. 
 
 Now here a very curious thing has been found ; mole- 
 cules of salt give twice as great a pressure as an equal 
 number of particles of sugar, spread through the same 
 volume of water ; it looks as if there were twice as many 
 particles of salt present. And it is supposed that there 
 really are twice as many. To account for this, it is 
 believed that each molecule of salt splits up into two 
 atoms, one of sodium and one of chlorine, and that each 
 atom plays the part of a molecule, in so far as it is able to 
 raise pressure. Owing to the habit which such minute 
 particles as the atoms of sodium and chlorine have of 
 
196 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 moving about in a watery solution, they are named ' ions,' 
 a Greek word, which means ' wanderers.' 
 
 But an ion is not merely a wandering particle; the 
 moving particles of sugar are not called ions. The ions 
 contained in a solution of salt have another peculiarity ; 
 one has gained, and the other has lost, what we may term 
 an atom of electricity. Now what is electricity ? 
 
 It used to be believed, formerly, that there were two 
 kinds of electricity, one called positive and the other 
 negative. At that time it would not have been possible 
 to answer the question. But recent researches make it 
 probable that what used to be called negative electricity 
 is really a substance. Indeed the relative weight of its 
 particles has been measured; each is about one seven- 
 hundredth of the mass of an atom of hydrogen : and the 
 mass of an atom of hydrogen is the smallest of all 
 masses of what we have been used to call matter. 
 
 Atoms of electricity are named ' electrons ' ; they appear 
 to be all of one kind. The metal sodium, and indeed all 
 other metals, may be regarded as compound of electrons 
 with a stuff which may be named ' sodion ' for sodium, 
 ' cuprion ' for copper, ' ferrion ' for iron, and so on. When 
 sodium loses an electron it becomes ' sodion ' ; when iron 
 loses three electrons it becomes ' ferrion,' and similarly 
 with the rest. 
 
 How can sodium be made to lose its electron ? This 
 happens when it enters into combination. When sodium 
 is heated in air, which contains oxygen gas, it burns, and 
 is said to unite or combine with oxygen ; burning appears 
 to be accompanied by a transference of an electron from 
 the sodium to the oxygen. Common salt may be made 
 by heating sodium in chlorine gas ; it takes fire, burns 
 and is changed into white ordinary salt. It has lost an 
 electron ; chlorine has gained one. 
 
 When dissolved in water, the sodium exists in the water 
 
WHAT IS ELECTRICITY ? 197 
 
 as sodion ; that is, sodium less an electron. The chlorine 
 is in the water, not as chlorine ; by gaining an electron, it 
 has been converted into chlorion. We see, therefore, that 
 those elements which we call metals become ions by 
 losing electrons; while those which we call non-metals 
 become ions by gaining electrons. 
 
 Let us now consider the simple battery or cell, consist- 
 ing of a plate of copper and a plate of zinc, dipping in a 
 jar half full of dilute hydrochloric acid. This hydro- 
 chloric acid consists of a number of ions of hydrogen; 
 and ions of hydrogen differ from ordinary hydrogen gas 
 in the same way as ions of sodium differ from metallic 
 sodium, namely, by each atom having parted with an 
 electron. The electron which each atom has lost has 
 attached itself to an atom of chlorine, and the chlorine 
 atom is thereby converted into an ion. 
 
 The plate of zinc cannot dissolve in the water, until its 
 atoms have been converted into ions. They would then 
 each have to part with two electrons. But the attraction 
 of an atom of zinc for these two electrons is so great that 
 the zinc does not dissolve, unless, indeed, the electrons 
 can be conveyed elsewhere. 
 
 Now electrons have the power of travelling through 
 metal; this point will be considered later; it must be 
 accepted for the present. When an atom of zinc gives up 
 its two electrons to the zinc plate, the atom of zinc which 
 lies nearest to that which has parted with these two elec- 
 trons will be overloaded ; it already is in combination with 
 its own two, and cannot unite with two additional ones ; 
 or, if it does, it must pass on its own electrons to the 
 neighbouring atom. 
 
 These two electrons, therefore, displace others, or, it may 
 be, are themselves transmitted through the zinc, until 
 they reach the copper wire. Copper, in the metallic 
 state, is also a compound of copper ions with two elec- 
 
198 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 trons ; and the copper, like the zinc, is overloaded by the 
 electrons from the zinc. Hence it transmits them to the 
 copper plate, and they find their way to the surface of the 
 plate. 
 
 There they find hydrogen ions, which are ready to com- 
 bine each with one electron in order to form hydrogen 
 atoms ; and having combined, the atoms of hydrogen 
 unite in couples, bubbles of hydrogen are formed, and 
 float up to the surface and burst. In short, the zinc 
 passes on its electrons through the copper wire to the 
 copper plate, when they are transmitted to the ions of 
 hydrogen in solution, and these first become atoms and 
 then molecules. 
 
 These conceptions, which are rather intricate, may be 
 rendered clearer by means of a diagram, a is the solu- 
 tion of hydrochloric acid in water ; b is the zinc plate ; 
 c is the copper plate, and d the connecting wire. H H, on 
 the left of the diagram, are two atoms of hydrogen, each 
 
 c b 
 
 EXPLANATION OF A GALVANIC CELL 
 
 of which has gained an electron ; they will unite together 
 to a molecule, and escape in a bubble up through the 
 
WHAT IS ELECTRICITY? 199 
 
 liquid. The electrons which they have gained have 
 followed the arrows from the zinc plate, along the copper 
 wire and down the copper plate. 
 
 A zinc atom minus its two electrons has left the zinc 
 plate ; it is now a zinc ion. These two electrons have dis- 
 placed other electrons from their combination with zinc 
 and copper ; and it is these electrons, or their substitutes, 
 which have attached themselves to the hydrogen ions. 
 There are hydrogen and chlorine ions in the liquid. The 
 hydrogen ions move toward the copper plate, and the 
 chlorine ions toward the zinc plate, but less rapidly. 
 
 Some of these will touch the zinc plate ; and if they 
 could pass round the circuit, through the wire, there 
 would be no electric pressure ; but it is because the plates 
 and the connecting wire are impervious to matter, while 
 they are pervious to electrons, that electric pressure or 
 to give it the usual name, electromotive force or potential 
 is developed. In fact, the metals and the wire are semi- 
 permeable membranes ; they allow electrons to pass, while 
 they block the passage of matter. 
 
 Perhaps the idea may be somewhat more easily grasped 
 if it is put in another form. Electrons do not pass 
 through water ; probably because the treble combination 
 of electrons, hydrogen, and oxygen is too firm to allow 
 of the transference of electrons from one molecule to 
 another. But when a salt is dissolved in the water elec- 
 trons can pass, for they easily transfer themselves from one 
 place to another, carrying along with them atoms such as 
 chlorine. Their progress is much impeded thereby ; but, 
 as explained before, they are easily transmitted through 
 metals, and thus, again, electric pressure is developed. 
 
 The analogy with ' osmotic pressure,' as the pressure of 
 the sugar molecules dissolved in water against a semi- 
 permeable membrane is called, is obvious; just as the 
 water in which the sugar is dissolved can pass in and out 
 
200 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 through the semi-permeable screen or partition, so the 
 electrons can pass backwards and forwards through the 
 metallic plates and wire; and just as the sugar molecules 
 are unable to traverse the membrane, so the matter with 
 which the electrons are in combination is unable to pass 
 through the metal. The metal is thus a semi-permeable 
 membrane, and electric pressure is developed in con- 
 sequence, in the same way as osmotic pressure is developed 
 by the sugar in solution. 
 
 If a 'weak solution of common salt be boiled down, after 
 sufficient water has been evaporated away, crystals of salt 
 separate out and deposit. Now the weak solution con- 
 tains the constituents of the salt almost entirely in the 
 state of ions ; that is, the sodion is without an electron, 
 which, if added, would convert it into the metal sodium ; 
 and the chlorion would be the element chlorine, if it 
 could part with its electron. 
 
 During concentration, as the water evaporates, the ions 
 of sodium and chlorine are brought nearer each other, 
 and they combine to form solid salt when enough water 
 has been removed. But even when combined to form 
 salt in the solid state, the electron does not leave the 
 chlorion and attach itself to the sodion ; if that happened 
 the result would be metallic sodium and chlorine gas; 
 and they are certainly not formed. A crystal of salt 
 differs from a solution of salt in much the same respects 
 as a piece of ice differs from water ; the one is solid and 
 the other is liquid ; but evidently the same stuff is there ; 
 the only difference is in the solidification. 
 
 It must therefore be supposed as a legitimate inference 
 that when a lump of sodium unites with chlorine and 
 burns in it as a lump of coal burns in air, the act of 
 combination consists of the transference of an electron 
 from the sodium metal to the chlorine ; the result of this 
 transference is to convert the sodium metal into sodions 
 
WHAT IS ELECTRICITY? 201 
 
 and the chlorine gas into chlorions. These are substances 
 with quite different physical and chemical properties from 
 the metal sodium and the gas chlorine. 
 
 On dissolving in a little water, some of the chlorions 
 and sodions, but only a few, become separated ; however, 
 if water be added so as to dilute the solution, a larger and 
 larger number separate, until at a sufficient dilution all 
 are separated. In fact, if this conception be extended, 
 all chemical combinations should be regarded as the 
 transference of electrons from one set of elements to 
 another. 
 
 But not all compounds are split into ions when they 
 are dissolved; it may be conjectured that in the case for 
 instance of such a compound as sugar, which dissolves in 
 water as such, the atoms of carbon, hydrogen, and oxygen, 
 of which it consists, have interchanged electrons, otherwise 
 chemical combination would not exist ; but that the ions 
 do not part from each other, even when opportunity is 
 given by dissolving the sugar in water. 
 
 Although facilities for motion in many cases lead to 
 separation of ions, it does not follow that when facilities 
 are present separation will always take place. 
 
 When common salt is melted, which takes place if it be 
 heated to redness, the ions separate ; that this is the case 
 is proved by its being then able to conduct electricity. 
 Melted glass is also a conductor, although solid glass is 
 not ; and the reason again is probably in the fact that the 
 ions have no freedom of motion in the solid. 
 
 These considerations, however, though closely connected 
 with the nature of ions, are not in such close touch with 
 the subject of this essay, the motive power of electricity. 
 Perhaps a last analogy may make the explanation which 
 I have tried to give somewhat clearer ; it is this : 
 
 Place a dilute solution of salt in one vessel and a 
 concentrated solution in another ; cover both vessels with 
 
202 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 a bell jar; pump out all air, so that the bell jar is filled 
 only with vapour of water, and leave the whole standing 
 for a long time. The weak solution will grow stronger, 
 for it will evaporate; and the strong solution will grow 
 weaker, for the vapour of water will condense in it. Now 
 imagine that the two salt solutions are placed, not under 
 the same bell jar, but under two separate bell jars, and 
 that these bell jars are connected by a pipe. In the 
 middle of this pipe is a little engine ; the pipe from the 
 weak solution enters the steam pipe of the cylinder, and 
 the pipe leading from the cylinder, which would in an 
 ordinary engine lead to the exhaust, is connected with the 
 bell jar containing the stronger salt solution; then, if the 
 engine is delicate enough, it will be driven by the current 
 of vapour passing from the weak salt solution to the strong 
 one. 
 
 Why? Because although steam can pass away from 
 the surface of the water, salt cannot ; the surface of the 
 water is a diaphragm which will allow steam to pass, but 
 which is impenetrable for salt. 
 
 The analogy with a battery is this: The zinc plate is 
 like the weak solution of salt ; when it dissolves, it gives 
 up electrons at its surface ; these electrons can pass along 
 the wire, which is the analogue of the steam-pipe; if 
 required, a small magneto-electric engine could be inter- 
 posed so that it would be driven by the current passing 
 through the wire, that is, by the stream of electrons, 
 just as the steam-engine is driven by the current of 
 steam. 
 
 On arriving at the copper plate the electrons combine 
 with hydrogen ions and escape ; and in this respect the 
 battery described resembles rather a high pressure engine. 
 But if desired the electrons may be kept in the system ; it 
 is only necessary to surround the copper plate with some 
 substance such as sulphate of copper, and the electrons 
 
WHAT IS ELECTRICITY ? 203 
 
 are retained by uniting with the copper ions, when copper 
 atoms will be deposited on the copper plate. 
 
 Just as the surface of the water forms a diaphragm 
 through which salt cannot pass, while steam can, so the 
 surface of the zinc plate forms a diaphragm through 
 which matter such as zinc, hydrogen, or chlorine ions 
 cannot pass, while electrons can, and they are also able to 
 be conveyed by the wire, as steam is conveyed through 
 the pipe. The motive power both of steam and electricity, 
 in a word, is due to their passing from a region where 
 their pressure is high to where it is low. 
 
THE AURORA BOREALIS 
 
 THE Northern Lights, or the Merry Dancers, as they are 
 often called, must have attracted attention in our country 
 ever since it was inhabited. But whether owing to their 
 frequent appearance they escaped chronicling, or whether 
 records of natural phenomena were regarded as unim- 
 portant, I can find no mention of them in Scottish records. 
 South of the border and across the English Channel 
 mention is occasionally made of them ; for in these more 
 southern regions their occurrence was sufficiently un- 
 common for the display to attract attention. They were 
 often supposed to portend disaster. An account of an aurora 
 seen in London in 1560 likens it to ' burning spears ' : 
 
 1 Fierce fiery warriors fight upon the clouds, 
 In ranks and squadrons and right form of war.' 
 
 An aurora was described by Cornelius Genune, Professor 
 at Lou vain, in 1575 ; several were seen by Michael Mestlin, 
 tutor to the famous Kepler, in 1580; and in April and 
 September 1581, and in September 1621, brilliant auroras 
 were chronicled. From that date until 1707 there is no 
 mention of an aurora having been seen. 
 
 It has long been known that the compass-needle, which 
 usually points northward, and is inclined at an angle to 
 the horizon (or is said to ' dip '), becomes disturbed and 
 oscillates when an aurora is seen in the sky. It was the 
 celebrated Halley 1 who, in 1714, hazarded the bold con- 
 jecture that the aurora was therefore a magnetic pheno- 
 
 1 Philosophical Transactions, xxix. No. 341. 
 
 205 
 
206 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 menon ; the oscillations of the compass may even exceed 
 ten minutes of arc, as observed by Mr. James Glaisher l in 
 1847. And many hypotheses have been brought forward 
 to account for the connection between the two simul- 
 taneous phenomena. The last few years have seen the 
 equipment of expeditions to Iceland, Finland, and Northern 
 America, which have had for their principal object the 
 observation of the earth's magnetic disturbances and the 
 corresponding auroral displays. Many theories have been 
 advanced, and it will be my task to try to bring them 
 before you, and to supplement them where they appear to 
 be wanting. 
 
 Let us first, however, listen to an eloquent description 
 of the Northern Lights from the pen of the celebrated 
 Alexander von Humboldt : 2 
 
 ' Low down in the distant horizon, about the part of the 
 heavens which is intersected by the magnetic meridian 
 (i.e. the point to which the compass-needle is directed), 
 the sky, which was previously clear, is at once overcast. 
 A dense wall or bank of cloud seems to rise higher and 
 higher, until it attains an elevation of 8 or 10 degrees. 
 The colour of the dark segment passes into brown or 
 violet, and stars are visible through the smoky stratum, 
 as when a dense smoke darkens the sky. A broad, 
 brightly luminous arch, first white, then yellow, encircles 
 the dark segment. . . . The luminous arch remains some- 
 times for hours together, flashing and kindling in ever- 
 varying undulations before rays and streamers emanate 
 from it and shoot up to the zenith. The more intense 
 the discharge of the northern light, the more bright is the 
 play of colours, through all the varying gradations from 
 violet and bluish-white to green and crimson. The mag- 
 netic columns of flame rise either singly from the luminous 
 
 1 Philosophical Transactions, Iviii. 
 
 2 Cosmos (Bohn's edit.), vol. i. p. 189. 
 
THE AURORA BOREALIS 207 
 
 arch, blended with black rays similar to thick smoke, or 
 simultaneously in many opposite points of the horizon, 
 uniting together to form a flickering sea of flame, whose 
 brilliant beauty admits of no adequate description, as the 
 luminous waves are every moment assuming new and 
 varying forms. Round the point in the vault of heaven 
 which corresponds to the direction of the inclination of 
 the needle, the beams unite together to form the corona 
 the crown of the northern light which encircles the 
 summit of the heavenly canopy with a milder radiance 
 and unflickering emanations of light. It is only in rare 
 instances that a perfect crown or circle is formed; but, 
 on its completion, the phenomenon has invariably reached 
 its maximum, and the radiations become less frequent, 
 shorter, and more colourless. The crown and the luminous 
 arches break up, and the whole vault of heaven becomes 
 covered with irregularly scattered broad, faint, almost 
 ashy grey, luminous, immovable patches, which in their 
 turn disappear, leaving nothing but a trace of the dark 
 smoke-like segment on the horizon. There often remains 
 nothing of the whole spectacle but a white, delicate cloud, 
 with feathery edges, or divided at equal distances into 
 small roundish groups, like cirro-cumuli/ 
 
 These phenomena are also visible in the Southern 
 hemisphere, and are produced by the Aurora Australis. 
 
 The luminous arches were also well described by Mr. 
 William Key in a letter to Dr. Priestley, published in the 
 Philosophical Transactions for 1783. He noticed that 
 the summit of the arch passed near or through the pole- 
 star; the arches were not always accompanied by the 
 ' dancers.' Key, following Canton unwittingly, connected 
 the aurora with discharges of electricity through rarefied 
 gases. His words are: 'Let me hazard a conjecture 
 respecting the white colour and stationary appearance of 
 some of these arches. Experiments in electricity, made 
 
208 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 with what is called an ' exhausted ' receiver, show that the 
 colour and motion of the electric spark vary in proportion 
 to the rarity of the air in the receiver. The more the air 
 is rarefied, the more movable and coloured is the electric 
 aura passing through it. On the contrary, the colour of 
 the spark approaches to whiteness, and moves with greater 
 difficulty, as the air is admitted. Will this observation 
 serve in any measure to account for the difference in 
 colour and motion of these electrical arches, for such I 
 presume to call them ? May we not suppose the more 
 coloured and brilliant portions of the aurora borealis to be 
 made in the rarer parts of the atmosphere, while the more 
 white and stationary ones possess the denser parts ? The 
 whitest arches which I saw were the most fixed/ 
 
 Repeated attempts have been made to ascertain the 
 height of an aurora. Henry Cavendish, the celebrated 
 chemist, calculated the height from the data furnished by 
 three observers of an aurora which was seen in 1784 one 
 of whom was stationed at Cambridge, one at Kimbolton 
 in Huntingdonshire, and one at Blockley in Gloucester- 
 shire by simple trigonometry, knowing the angle which 
 the summit of the arch appeared to subtend with the 
 horizon in each case ; the results are very reasonably con- 
 cordant, and give an altitude of 52 to 71 miles. Many 
 subsequent attempts have been made, and with similar 
 results. One of the latest writers, Professor Birkeland, 
 of Christiania, gives as limits 62 to 124 miles (100-200 
 kilometres). The difficulty in such observations is to 
 make sure that the observers in different places have 
 been measuring the same arch at the same moment. I 
 shall have occasion later to bring evidence of a totally 
 different character to confirm the general accuracy of such 
 measurements. 
 
 Between the years 1786 and 1793 John Dalton, who 
 was as indefatigable a meteorologist as he was a distin- 
 
THE AURORA BOREALIS 209 
 
 guished chemist, observed, from Kendal and Keswick, in 
 Cumberland, no fewer than 250 displays of northern 
 lights ; he established the fact that the highest part of the 
 luminous arc lies exactly above the magnetic pole, and 
 that the streamers are parallel, at least ' over a moderate 
 extent of country,' with the compass-needle as it dips 
 towards the magnetic pole, which is believed to exist in 
 the north of Canada, within the Arctic circle. 
 
 The celebrated De la Rive, of Geneva, made an attempt 
 to reproduce the aurora in the interior of a glass vessel. 1 
 He started from the fact that the atmosphere is always 
 charged with positive electricity, and that the earth is 
 negatively electrified ; he presumed, accordingly, that the 
 two kinds of electricity would neutralise one another, and 
 that currents would, as a rule, rise vertically to the earth's 
 surface. Neutralisation occurs slowly when rain or snow 
 falls, and suddenly when lightning flashes. De la Rive's 
 theory is that in the upper regions of the atmosphere 
 electric currents circulate from the equator to the two 
 poles ; and terrestrial currents, in the interior of the earth, 
 are continually flowing from the poles towards the 
 equator. Conduction, he thought, would be easier in the 
 higher than in the lower regions of the atmosphere, and 
 also better at the poles than near the equator, because of 
 the moisture and frequent mists in the polar atmosphere. 
 The discharge through the polar air would, he believed, 
 render the mist luminous, and thus produce the pheno- 
 mena already described. 
 
 His apparatus, which I had the good fortune to see in 
 September 1902 at Geneva, consisted of a globe with a 
 neck at each ' pole.' Through one of these necks passed 
 a copper rod A, one end of which was connected with the 
 positive discharge of an electrical machine ; at the other 
 end a ring of copper B was attached. G is an insulated 
 
 1 Memoires de la Soc. de Phys. et d 'His. Nat. de Geneve, vol. xiii. 
 
 O 
 
210 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 soft-iron bar covered with an insulating composition, and 
 projecting through the opposite neck of the flask. By 
 touching the exposed end of this rod with an electro- 
 
 DE LA RIVE'S APPARATUS FOR REPRODUCING THE AURORA 
 
 magnet D, it also became a magnet. The air in the globe 
 having been rarefied, a brush discharge took place between 
 the ring B and the end of the rod (7; on making C a 
 magnet, the discharge became more luminous and regular, 
 and revolved round the magnet, sending streamers towards 
 the' end of the rod. In De la Rive's model the copper 
 ring represents the atmosphere, from which electricity 
 discharges to the rod C, representing the earth. He con- 
 cluded that the aurora forms a luminous ring round the 
 magnetic poles as centres, with a greater or less diameter, 
 the ring rotating on account of the earth's magnetism; 
 that it is due to a discharge from the positively electrified 
 atmosphere to the negatively electrified earth, the separa- 
 tion of the two kinds of electricity being caused by the 
 action of the sun, chiefly in equatorial regions; that 
 discharges are of constant occurrence, though with very 
 varying intensities, and that the cirro-cumulus clouds are 
 also illuminated by such discharges. 
 
 When the spectroscope was turned on the aurora the 
 presence of a green line of wave-length about 5570 units 
 
THE AURORA BOREALIS 211 
 
 was noticed. Different observers gave : Angstrom, 5568 ; 
 Vogel, 5572; Vijkander, 5573; Lemstrom, 5570; Huggins, 
 5570-4; Copeland, 5573; Gyllenskjold, 5569; Campbell, 
 5571-6; Sykera, 5570; the Danish Mission to Iceland in 
 1899-1900, 5570. Many other lines have been photo- 
 graphed, of which more hereafter ; but this line is extra- 
 ordinarily intense, and, indeed, can often be seen when 
 there is no visible aurora by simply directing a pocket 
 spectroscope towards the north. The line when first 
 observed was not known to be characteristic of the 
 spectrum of any element. 
 
 In 1898 I had the honour to announce to the Royal 
 Society the discovery, in conjunction with my assistant, 
 Dr. M. W. Travers, of the existence of three new elemen- 
 tary substances in the atmosphere, to which we gave the 
 names neon, or ' the new one ' ; krypton, or ' the hidden 
 one ' ; and xenon, or ' the stranger.' 
 
 The spectrum of neon is characterised by many lines 
 in the red, orange, and yellow ; while that of xenon 
 shows many green and blue lines. The light evolved 
 from tubes containing these gases under low pressure 
 when an electric 'current of high tension is passed through 
 them, is of a corresponding hue ; thus neon sends out a 
 splendid rose or flame-coloured light ; and xenon, a sky- 
 blue ; while the light of krypton is nearly white, although 
 seen by some of a pale lilac, and by others of a pale-green 
 colour. 
 
 The densities of the elements proved to be as had been 
 expected : that of neon, compared with hydrogen taken as 
 2, is 20 ; of krypton, 82 ; and of xenon, 128. 
 
 Shortly after the discovery of krypton, my assistant, 
 Mr. Baly, measured carefully the wave-lengths of its more 
 important lines ; and one of these, a very brilliant green 
 line, had the wave-length 5570*5. The day after this 
 was published, Sir William Huggins wrote me privately 
 
212 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 pointing out the identity of this wave-length with the 
 principal auroral line ; and a week later, Professor Arthur 
 Schuster, in a letter to Nature, called attention to the 
 same coincidence. 
 
 It therefore appeared probable that the aurora might 
 be produced by electric discharges in the upper atmo- 
 sphere, through a gas in which krypton was present in 
 considerable amount. 
 
 In the meantime Professor Paulsen, of Copenhagen, 
 has been examining the photographed spectra of the 
 aurora collected by the Icelandic and Finland expeditions; 
 and it appears probable that many of the lines seen in the 
 auroral spectrum are identical with those of the common 
 gas nitrogen, seen at the cathode terminal of a vacuum- 
 tube. Professor Paulsen has had the great kindness to 
 send me prints of two photographs, the lines of which are 
 numbered I. and II. in the following table. I have added 
 in a parallel column the corresponding wave-lengths of 
 krypton lines. 
 
 Lines of auroral and of cathode Lines of 
 
 nitrogen spectrum. krypton. Intensity. 
 
 I. II. 
 
 1 Absent. 3140 
 
 2 3160 
 
 3 3370 
 
 4 Absent. 3540 
 
 5 3580 3580 3590 7 
 
 c 3718 10 
 
 6 3710 Absent. < 3719 8 
 
 I 3721 7 
 
 7 3760 3760 3754 5 
 
 8 3800 3800 3805 4 
 
 9 3920 3920 3920 8 
 
 f 3995 6 
 
 10 400 * 00 I 3998 5 
 
 
THE AURORA BOREALIS 213 
 
 Lines of auroral and cathode Lines of 
 
 nitrogen spectrum. krypton. Intensity. 
 
 I. II. 
 
 11 4060 4060 4057 8 
 
 12 4260 4260 4274 8 
 
 13 5570 Absent. 5570 10 
 
 The last is the characteristic line of the aurora, and is one 
 of the two brilliant lines of the krypton spectrum; the 
 other brilliant krypton line is in the yellow, and cannot 
 be easily photographed when the light is not bright but 
 flickering, as the auroral light is. 
 
 I ain not able to decide yet whether the lines are all 
 due to krypton or to the cathode spectrum of nitrogen. 
 Certainly there is a striking similarity between the 
 nitrogen spectrum and that of the aurora ; and, on the 
 other hand, the lines of krypton, though sufficiently 
 coincident with those of the aurora to satisfy criticism, 
 leave other bright lines of the krypton spectrum un- 
 accounted for. Yet the cathode spectrum of nitrogen 
 does not contain the line 5570, the most brilliant of the 
 auroral spectrum, and the one most easily discovered by 
 aid of a pocket spectroscope. Experiments on this matter 
 are not yet decisive. 
 
 Moreover, it appears improbable that the aurora should 
 always exhibit only one spectrum. The discharge of 
 electricity through a mixture of gases reveals more or less 
 completely the spectrum of each. Those gases which are 
 present in smallest amount have, as a rule, their spectra 
 proportionately enfeebled. But it does not always happen 
 that all the lines of the spectrum of any one gas are 
 proportionately enfeebled ; sometimes the character of the 
 spectrum itself is altered. The interposition of a Leiden 
 jar and a spark-gap often causes a radical alteration in 
 the spectrum of a gas. This can be well seen with argon ; 
 when the discharge is altered, many of the red lines of the 
 
214 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 spectrum disappear and blue lines become visible ; hence 
 the colour of the discharge changes from red to blue. 
 And other gases exhibit the same kind of change, though 
 not generally in so striking a manner. Further, it has 
 been shown by my colleague, Dr. Collie, that an element 
 may develop a new and strong line in its spectrum 
 on being mixed with a certain gas, which it does not 
 exhibit if another gas be substituted. All these questions 
 are very obscure, and have not as yet been investigated ; 
 only the fringe of the subject has been touched. As the 
 aurora, without doubt, is visible on different occasions at 
 very different altitudes, it is more than possible that the 
 spectra will differ. The appearance of red auroras would 
 imply a spectrum in which red lines predominate ; but I 
 am not aware of any observation having been made of the 
 spectrum of a red aurora. From the similarity of colour 
 it might well be conjectured that the red tint is due to 
 the discharge occurring through an atmosphere compara- 
 tively rich in neon. 
 
 Assuming for the moment the identity of the line of 
 wave-length 5570 with that of krypton, two questions at 
 once suggest themselves. First, why should this line be 
 so remarkably brilliant when krypton is present in the 
 atmosphere in comparatively very minute amount ? 
 What are the relative intensities of the spectra of krypton 
 and of other gases under similar circumstances ? And 
 second, is there any process which will tend to increase 
 the relative amount of krypton in the upper regions of 
 the atmosphere ? I have attempted to answer both these 
 questions. 
 
 Some years ago, in conjunction with Professor Collie, 
 
 experiments were made on the visibility of the spectrum 
 
 of one gas in presence of another with which it was 
 
 diluted. 1 The results are given in the following table: 
 
 1 Proc. Roy. Soc., lix. 257. 
 
THE AURORA BOREALIS 215 
 
 AMOUNT OF GAS DETECTABLE IN A MIXTURE 
 
 1. Helium in hydrogen, 10 per cent, of helium barely visible. 
 
 2. Hydrogen in helium, O'OOl ,, of hydrogen visible. 
 
 3. Nitrogen in helium, O'Ol of nitrogen almost invisible. 
 
 4. Helium in nitrogen, 10 of helium difficult to detect. 
 
 5. Argon in helium, 0'06 still visible. 
 
 6. Helium in argon, 25 invisible. 
 
 7. Nitrogen in argon, 0'08 just visible. 
 
 8. Argon m nitrogen, 37 barely visible. 
 
 9. Argon in oxygen, 2 '3 ,, difficult to distinguish. 
 
 This table shows the enormous differences which exist 
 between the behaviour of different gases. To take the 
 extreme cases while it is possible to detect 1 part of 
 hydrogen in 100,000 of helium, it is barely possible to 
 recognise 1 part of argon in 2 of nitrogen. 
 
 Similar experiments with krypton showed that 
 In air, 1 part of krypton is visible in 7,100 parts. 
 
 In oxygen, 1 1,250,000 
 
 In hydrogen,! 67 
 
 In argon, 1 7,150 
 
 In helium, 1 ' 2,860,000 
 
 The pressure of krypton, too, in the case of air is almost 
 inconceivably low ; it amounts to only one thirty-millionth 
 of the usual atmospheric pressure. This shows the enor- 
 mous persistency of the krypton spectrum that is, of the 
 most conspicuous line, the auroral green, for that was the 
 one observed in all instances. If, then, an electric dis- 
 charge passes through the upper and rarefied strata of the 
 atmosphere, the probability of detecting the green line of 
 krypton will be much greater than that of detecting the 
 spectrum of any other element, even though the latter 
 be present in enormously greater proportion. Hydrogen 
 alone has any marked power of extinguishing the spectrum 
 of krypton. 
 
 It is possible to calculate the maximum height of the 
 aurora, on the supposition that the krypton line is no 
 
216 ESSAYS BIOGEAPHICAL AND CHEMICAL 
 
 longer visible when the pressure falls below 0*000035 
 millimetre the pressure observed when, in a mixture of 
 krypton and helium, the green line of krypton became 
 very faint and almost invisible. Neglecting the influence 
 of temperature, the pressure of the atmosphere can be 
 made to give its height by the formula 
 
 H = 18-382 (log. B-log. b) kilometres. 
 Substituting for B (barometer) its normal height, 760 
 millimetres, and for b the pressure of the krypton, 0-000035 
 millimetre, we have height = 135 kilometres, or about 84 
 miles. This number is reasonably near the figures given 
 by Cavendish and others. Professor Birkeland, the latest 
 authority, it will be remembered, thinks the altitude is 
 from 100 to 200 kilometres, 1 or from 62*5 to 125 miles. 
 
 We may next ask Since the spectrum of krypton is 
 so persistent, why is it not visible in air ? The answer is 
 Because the presence of nitrogen renders it invisible, 
 for it is not possible to distinguish less than one part of 
 krypton by volume in 7100 parts of air. But krypton 
 does not show its spectrum in argon, which may be said 
 to constitute about 1 per cent, of the volume of air. Now 
 7100 parts of air will yield about 70 parts of argon, and it 
 should be possible to distinguish the krypton line if the 
 amount of krypton present wee O'Ol part, or 1 part in 
 7000. This would give, for the proportion of krypton 
 in air, 1 part in 700,000. Recent experiments, have 
 shown that it is possible to extract 1 part of krypton 
 from about 7,000,000 of air ; and of xenon, which, owing 
 to its lower vapour pressure, can be extracted from air 
 with more ease than krypton, there is only about 1 part 
 in 40,000,000 of air. It is therefore clear why the spec- 
 trum of krypton is not visible in that of crude argon. 
 
 We come next to the question Is there any reason 
 to believe that krypton may concentrate in the higher 
 
 1 Expedition Norv&gienne, Christiania, 1901, p. 28. 
 
THE AURORA BOREALIS 217 
 
 regions of the atmosphere, that is, that its proportion, 
 relatively to that of the more abundant gases oxygen and 
 nitrogen, may increase as the altitude grows greater ? To 
 this, I think, an affirmative answer may be given. Let us 
 consider the grounds for the supposition. 
 
 When a gas is compressed it turns warm, as every one 
 knows who has used a bicycle-pump. Conversely, when 
 it escapes from compression it cools itself. But all gases 
 do not heat or cool equally for equal amounts of compres- 
 sion or expansion ; for some gases are raised to a higher 
 temperature than others by absorbing the same quantity 
 of heat; and the same quantity of heat is, practically, 
 generated by the same degree of compression, or absorbed 
 by the same degree of expansion; for work is quanti- 
 tatively equivalent to heat, as was shown by Joule half a 
 century ago. Now 40 grams of argon should, if the 
 specific heat of that gas were the same as that of oxygen, 
 require the same amount of heat to raise its temperature 
 through 1 degree ; or put in another way, if each of these 
 gases were expanded to the same amount, they would be 
 equally cooled, if equal amounts of heat were requisite to 
 raise their temperatures through an equal number of 
 degrees. But this is not the case. Argon requires less 
 heat to raise its temperature than oxygen, in the ratio of 
 3 to 5 if it is not allowed to expand, or in the ratio 
 of 5 to 7 if expansion is possible under constant pressure. 
 If allowed to expand under circumstances in which volume 
 increases while pressure falls, some ratio intermediate 
 between these would show the difference in cooling ; the 
 exact amount depending on the degree of expansion in 
 question. Broadly stated, argon, in expanding will cool 
 itself considerably more than oxygen or nitrogen ; while its 
 congeners, helium, neon, krypton, and xenon, will exhibit 
 a degree of cooling practically identical with that of argon. 
 
 The next point to be considered is that gases diffuse 
 
 
218 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 freely into one another when left in contact; so that a 
 heavy gas will mix readily with a much lighter one, even 
 though the heavy one may be below and the lighter one 
 above. This diffusion results from the motion of the 
 molecules of gases ; and as the rate of motion depends on 
 the temperature of the gas, those molecules which happen 
 to have a high temperature move much more rapidly than 
 those with a lower. When two gases mix, however, or 
 when a hot gas mixes with a cold one, the more rapidly 
 moving, and therefore hot, molecules very rapidly com- 
 municate their motion to the colder gas, raising its 
 temperature until the temperatures of both sets of mole- 
 cules are equalised. This is due to the enormous number 
 of encounters which take place between the molecules, 
 partly on account of the minute size of each molecule, 
 and the consequent number in even a very small volume ; 
 and partly to the great rate at which they are moving. 
 For example, it can be calculated that in all probability 
 there are 50,000,000,000,000,000 or 50 quadrillion mole- 
 cules of hydrogen in a cubic millimetre of that gas (about 
 the volume of the head of a large pin) and that the 
 average velocity of each molecule is at the rate of 4J miles 
 per second. No wonder, therefore, that the exchange 
 between molecules of different temperature is almost 
 instantaneous. It must nevertheless be borne in mind 
 that hot gases diffuse much more rapidly than cold ones. 
 The densities of the gases constituting the atmosphere 
 are as follows, the standard being that of oxygen taken as 
 16:- 
 
 Water Vapour, 9 0-333 Neon, 10 0-316 
 
 Nitrogen, 14 0'287 Argon, 20 0'224 
 
 Oxygen, 16 0'250 Krypton, 41 0156 
 
 Carbon Dioxide, 22 0*213 Xenon, 64 0125 
 
 Helium, 2 0'707 - 
 
THE AURORA BOREALIS 219 
 
 The relative rates of diffusion are inversely as the 
 square roots of the densities, and are given in the second 
 column. For example, oxygen escapes into a neighbour- 
 ing layer twice as quickly as xenon ; and helium nearly 
 three times as fast as oxygen. Now it is evident that the 
 gases which will escape most slowly are krypton and 
 xenon; carbon dioxide and argon come next in order; 
 while nitrogen, neon, water vapour, and helium escape 
 more rapidly in the order given. If then a jar with 
 porous walls were full of air, and were exposed to some 
 indifferent atmosphere, the gas remaining in the jar after 
 some time would contain more of the heavier and less of 
 thelighter gases proportionally to the original amounts 
 present. 
 
 The third premiss in the argument is that in equatorial 
 regions there is an upward current of air, due to the 
 warming of the earth by the nearly vertical rays of the 
 sun and the consequent expansion of the air in contact 
 with the soil or the sea ; while in the polar regions there 
 is a continual downward current, produced by the cooling 
 of the air in contact with the ice of the polar caps. This 
 circulation of the atmosphere was investigated by Professor 
 James Thomson in 1857, and his Bakerian lecture on the 
 subject appeared in the Philosophical Transactions for 
 1892, p. 653. The conclusion to which he came is that 
 the upward atmospheric current at the equator on reaching 
 the higher regions of the atmosphere, divides into two, 
 and while one part of the air travels in a north-easterly 
 direction, the other half travels in a south-easterly direction 
 towards the north and south poles respectively. Arrived 
 at the neighbourhood of the polar caps, the air descends 
 and, broadly stated, travels back near the surface of the 
 earth again towards the equator. We need not here regard 
 eddies which occur near the tropics of Cancer and Capri- 
 corn ; the main features are sufficient for our purpose. 
 
220 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 The air, then, as it ascends from equatorial latitudes 
 cools itself in the process ; and from what has been said, 
 it would seem that gases of the argon group would cool 
 more rapidly than the other atmospheric gases, oxygen 
 and nitrogen. Pour prdciser les idtes, as the French say, 
 let us confine our attention to the northern hemisphere, 
 and let us suppose that a vertical partition has been set 
 up in the neighbourhood of the equator, quite permeable 
 to gases, and surrounding the earth much as the wooden 
 frame of a terrestrial globe surrounds the globe. Indeed, 
 if we conceive of that frame as a double one, and the 
 ascending current rising between the walls, we shall 
 realise what is intended. As the upward current gains in 
 height, it falls in temperature ; and during the whole of 
 the ascent the nitrogen and oxygen are passing through 
 the porous diaphragm at a rate greater than that of the 
 argon gases. With increasing height the density of all 
 gases decreases ; their molecules are more widely separated 
 from each other, and interchange of velocity or, what is 
 equivalent, interchange of temperature becomes less rapid ; 
 hence the separation should be a more perfect one the 
 greater the altitude. But, at the same time, the argon 
 gases are not wholly left in the upward current; many 
 molecules will pass the barrier; why should they not 
 return in as great number as they pass ? Because after 
 passing the partition they no longer move upwards with 
 the same velocity as before; the farther they progress 
 towards the north the less inducement to rise, for the 
 temperature of the earth is lower. 
 
 This reasoning is equally applicable if we regard the 
 barrier as removed ; we may mentally surround the earth 
 with an infinity of such barrier rings, parallel to the plane 
 of the equator ; and it will still remain true that the 
 warmer gases will tend to escape in the lower regions 
 of the atmosphere, leaving the cooler gases to ascend. 
 
THE AURORA BOREALIS 221 
 
 At the poles the process is reversed. The argon gases 
 are more heated during their descent than the oxygen and 
 nitrogen, and will escape into neighbouring layers of 
 atmosphere at a greater altitude, on the average, than the 
 latter. The relative rates of diffusion of these gases, too, 
 may play an even more important part in effecting the 
 separation ; the heaviest argon, carbon dioxide, krypton, 
 and xenon will remain in the ascending layer in larger 
 relative proportion than the oxygen, nitrogen, and other 
 lighter gases, and will, therefore, be carried to the upper 
 regions of the atmosphere by the ascending equatorial 
 current ; but in the descending polar current the process 
 would be reversed, for the heavier gases would be carried 
 down in the current with less escape than the lighter 
 ones. The effect of diffusion alone, neglecting the heating 
 or cooling of the gases, would, therefore, be neutralised 
 during each complete circulation. 
 
 But the process of separation which depends on the 
 difference of temperature of the gases, were there only one 
 circulation, would in all probability be productive of very 
 small result; it is to be observed, however, that the effect 
 is cumulative, that the process of concentration of the 
 argon gases in the higher regions of the atmosphere goes 
 on from age to age, and that there may now be an 
 apparently stationary state, when separation of argon 
 gases from oxygen and nitrogen balances mixture by 
 diffusion and the mixing which inevitably accompanies 
 winds. It may be suggested that the greater frequency 
 of auroras during years when the sunspots are large and 
 easily visible may be connected with the higher tempera- 
 ture of such years, as well as with the magnetic disturb- 
 ances which invariably accompany sunspots. 
 
 To sum up : 1. The gases of the argon group are more 
 easily heated and cooled than are oxygen and nitrogen, 
 2. They are cooled more than the latter during their 
 
 
222 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 upward ascent at the equator, and therefore tend to con- 
 centrate in the ascending current as it reaches the con- 
 fines of the atmosphere, owing to the more rapid escape 
 of oxygen and nitrogen by diffusion. 3. The phenomena 
 are reversed in the descending currents at the poles, and 
 the argon gases tend to mix with neighbouring layers of 
 gas at high altitudes. 4. The higher strata of the atmo- 
 sphere are probably richer in the inactive gases than the 
 lower strata. 
 
 As electric discharges producing the aurora certainly 
 occur at great altitudes, the spectra seen are those of the 
 inactive gases; and owing to the fact that the krypton 
 green line, of wave-length 5570 units,, is remarkably easily 
 visible, even in an admixture of other gases, it happens to 
 be the most conspicuous line in the auroral spectrum. 
 
 This leads us to consider, in the last place, the cause of 
 the electric current. And here we enter on a different 
 region of thought. 
 
 There are two theories on the subject, one due to Pro- 
 fessor Birkeland, 1 of Christiania, the other to Professor 
 Arrhenius, 2 of Stockholm. It has long been known that 
 violet light rays and the invisible rays of the spectrum 
 beyond the violet, which can be detected by photography, 
 have the property of discharging a negatively electrified 
 body. It is suggested by Professor Birkeland that the 
 spots on the sun are caused by solar eruptions, or, to use a 
 familiar word, volcanoes ; and that the sun then emits 
 negatively charged corpuscles, similar to those which are 
 believed to constitute, partly at least, the cathode rays 
 rays producing those utilised for surgical practice in taking 
 photographs of bones. Birkeland supposes that such 
 corpuscles are ' sucked in ' to the earth's magnetic poles, 
 giving rise to vortices of electric currents in the upper 
 
 1 Archives des Sciences Phys. et Nat. tie Geneve, June 1896. 
 
 2 Physikalische Zeitschrift, ii. Nos. 6 and 7. 
 
THE AURORA BOREALIS 223 
 
 regions of the atmosphere. It is indeed known that such 
 rays are deviated by the neighbourhood of a magnet ; and 
 also that the presence of large solar spots is always 
 accompanied by magnetic ' storms ' on the earth and the 
 appearance of frequent and brilliant auroras. 
 
 The theory of Arrhenius is that the corpuscles emitted 
 by the sun are not inconceivably minute bodies, but have 
 an appreciable size ; that they are, say, the thousandth of 
 a millimetre, or the 25,000th of an inch in diameter, and 
 that they are expelled from the sun by the repulsive 
 action of light. 
 
 Whichever theory be correct, it is probable that nega- 
 tively electrified gaseous molecules are present in the 
 upper regions of the atmosphere, and it is also probable 
 that these molecules receive their charge most readily 
 where they are most exposed to a vertical sun, that is, at 
 and near the equator. We have seen that Professor James 
 Thomson's upper aerial currents would carry these and 
 other molecules towards the poles; they would move 
 spirally northwards and southwards with an easterly 
 trend. As they approach the poles their number per unit 
 area will obviously increase ; for the terrestrial parallels of 
 latitude decrease in circumference the nearer they are to 
 the poles. It is to be expected that before the actual poles 
 are reached, the potential of the upper air should increase 
 to such an extent as to produce a luminous discharge, in 
 the form of a ring or halo, with the magnetic poles as 
 their centres. It is conceivably this ring which we see as 
 an arch in the sky; it may not be so high-as the coloured 
 streamers, and may well give the nitrogen spectrum. It 
 must be remembered, however, that the earth is a huge 
 magnet; and that lines of force connect the poles in a 
 fashion shown in the figure. The halo, exposed to these 
 magnetic forces, will send out streamers towards the poles 
 as well as towards the zenith; as they approach the 
 
224 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 equator, however, the light will fade, owing to the spread- 
 ing and weakening of these lines. 
 
 An imperfect attempt has been made to imitate the 
 auroral phenomena, but it nevertheless shows in some 
 degree the appearance of the northern lights. A globe, 
 containing krypton at very low pressure, is suspended 
 between the poles of a powerful electro- magnet ; 1 a ring, 
 consisting of five or six coils of covered wire, is laid on 
 the top of the globe, and by help of an induction-coil and 
 a Leiden jar, strong induction discharges are made to 
 pass through the coil. Each discharge is accompanied by 
 a circular discharge in the interior of the globe. The 
 effect is that of a ring or halo near the upper side of the 
 jar. On 'making' the electro-magnet, the ring sends 
 out streamers, exactly similar in appearance to auroral 
 streamers, and like them they have a rotary motion and 
 flicker, shortening and lengthening, just as natural 
 streamers do. If it were possible to place a magnetic 
 model of the earth inside such a globe, I doubt not that 
 the streamers would follow directions similar to those in 
 the figure, and that the imitation would still more closely 
 resemble the reality. The light evolved from pure 
 krypton, under the influence of such discharges, is of a 
 whitish steel-blue colour with occasional green and lilac 
 flickers, and it also recalls the appearance of the natural 
 aurora. But, as already remarked, it is more than 
 probable that the spectrum of the aurora, seen at different 
 times and in different altitudes, may show not only the 
 spectrum of krypton, but also those of the other atmo- 
 spheric gases. 
 
 One more remark before concluding. The temperature 
 of the upper atmosphere is undoubtedly very low ; but at 
 such altitudes even xenon, the least volatile of the atmo- 
 spheric gases, possesses so high a vapour pressure that it 
 
 1 The electro'inagnet belonging to a small 1 h.p. dynamo was used. 
 
DIAGKAM OF THE EARTH AND THE POLAR AURORAS 
 
 Facing page 224 
 
THE AURORA BOREALIS 225 
 
 would certainly remain gaseous ; for in order to liquefy or 
 solidify a gas, not merely reduction of temperature, but 
 also considerable pressure, is required. It is, however, 
 quite possible that water-vapour, in the lower regions 
 frequented by the aurora, may exist in a supersaturated 
 condition, and that the electric discharges may bring 
 about condensation, and on the large scale of nature, as 
 on the small scale of a laboratory experiment, produce 
 mists, and so give rise to the cirro-cumulus clouds which 
 so often accompany an aurora. 
 
 The solving of conundrums has for many people a great 
 attraction; Nature surrounds us with conundrums, and 
 it is one of the greatest pleasures in life to attempt 
 their solution. Whether or not I have been successful 
 in offering a partial solution of the one which we may 
 call the ' Merry Dancers,' time will show. 
 
THE FUNCTIONS OF A UNIVERSITY 
 
 ORATION DELIVERED AT UNIVERSITY COLLEGE, LONDON 
 JUNE 6, 1901 
 
 I AM about to speak of the Functions of a University. 
 The word University has borne many significations ; and, 
 indeed, its functions are various, and the signification 
 attached to the word has depended on the particular point 
 of view taken at the time. An eminent German, who 
 visited me some years ago, made the remark after seeing 
 University College: 'Aber, lieber Herr College, University 
 College ist eine kleine Universitat.' So it is ; for it fulfils 
 most of the functions of the most successful Universities in 
 the world. A countryman of the gifted founder of this 
 College, Thomas Campbell, a man who has left even a 
 deeper mark than he on the literature of the world, 
 
 said : 
 
 ' wad some Pow'r the giftie gie us 
 To see oursels as ithers see us ! 5 
 
 Were that gift given us, I am confident that we should 
 have no cause to blush. One of the most necessary 
 conditions of success is confidence in oneself 'a gude 
 consait of oursels,' as the Scots saying has it; and I 
 know that learned men throughout the world look on the 
 work done at University College as among the best pro- 
 duced. And why is this ? Because the traditions of 
 University College have always been that it is not merely 
 a place where known facts and theories should be ad- 
 
228 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 ministered in daily doses to young men and young women, 
 but that the duty of the professors, assistant-professors, 
 teachers, and advanced students is to increase knowledge. 
 That is the chief function of a University to increase 
 knowledge. But it is not the only one. 
 
 A University has always been regarded as a training 
 school for the ' learned professions,' i.e. for Theology, Law, 
 and Medicine. The terms of our charter have excluded 
 the first of these branches of knowledge. Founded as it 
 was in the 'twenties, when admission to Oxford or Cam- 
 bridge involved either belief in the tenets of the Church 
 of England, or insincerity, it was not possible to provide 
 courses in Theology which should be acceptable to Non- 
 conformists, Jews, and others who desired education. On 
 the whole, it appears to me better that a subject, about 
 which so much difference of opinion exists, should be 
 taught in a separate institution. There are many branches 
 of knowledge which can be adequately discussed without 
 intruding into any sphere of religious controversy ; and, 
 indeed, it would be difficult, I imagine, to treat mathe- 
 matics or chemistry from a sectarian standpoint. I, at 
 least, have never tried. There are subjects which may be 
 placed on the border-line, for example, Philosophy; but 
 such subjects, and they are few in number, might well 
 form part of the curriculum of the theological college, if 
 thought desirable. It is a thousand pities that instead 
 of founding King's College, a theological college had not 
 been established in the immediate neighbourhood of 
 University College ; it would have strengthened us, and it 
 would have tended, too, to the advantage of the Church 
 of England. However, what is done can't be undone; 
 and let us wish all prosperity to our sister college, and 
 a long and useful life. We are now friends, and have 
 been friends for many years. May that friendship long 
 continue ! 
 
THE FUNCTIONS OF A UNIVERSITY 229 
 
 Dismissing the Faculty of Theology, therefore, as out of 
 our power, as well as beyond our wishes, let us turn to the 
 remaining two learned professions. University College, I 
 believe, was the first place in England where a systematic 
 legal education could be obtained. Our chairs of Roman 
 Law, Constitutional Law, and Jurisprudence were the first 
 to be established in England, although such chairs had 
 for long been known on the Continent and in Scotland. 
 ' Imitation is the sincerest flattery ' ; and in the fulness of 
 time, the Inns of Court started a school of their own. 
 Our classes, which used to be crowded, dwindled, and our 
 law-school is certainly not our strongest feature. I am 
 not sufficiently acquainted with English legal education 
 to pronounce an opinion as to whether methods of train- 
 ing as they at present exist in England are the most 
 effective : I have heard rumours that they are not. That 
 must be left to specialists to decide. But arguing from 
 the experience of another faculty, in which the apprentice- 
 ship system once existed, and which has changed that 
 system with a view to reform, and judging, too, from 
 experience abroad and in Scotland, I venture to think 
 that some improvement in legal education is possible. If 
 that opinion is correct, it is surely not too much to hope 
 that the claims of University College may be considered 
 as having made the first attempt to systematise legal 
 education in England. 
 
 The Faculty of Medicine has existed in a flourishing state 
 since the inception of University College. Not long after 
 the College was built, the old Hospital buildings, were 
 erected. One of my predecessors, on a similar occasion to 
 this, has given you an entrancing account of the early 
 history of this side of the College, and has discoursed on 
 the eminent men who filled the chairs in the Medical 
 Faculty. Here young men whose intention it is to enter 
 the medical profession are trained ; they now receive five 
 
230 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 years' instruction in the various branches of knowledge 
 bearing on their important calling. I would point out 
 that this function of a University is professedly a technical 
 one : the training of medical men. True, many researches 
 have been made by the eminent men who have held 
 chairs in this Faculty ; but that is not the primary duty 
 of such men ; their duty is to train others to exercise a 
 profession. If they advance their subject in doing so, so 
 much the better ; it increases the fame of the school, it 
 imparts enthusiasm to their students, and in many cases 
 their discoveries have been of unspeakable benefit to the 
 human race. In a certain sense, every medical man is an 
 investigator ; the first essential is that he shall be able to 
 make a correct diagnosis ; the next, that he shall prescribe 
 correct treatment. But novelty is not essential ; few men 
 evolve new surgical operations or introduce new remedies; 
 and though we have in the past had not a few such, they 
 are not essential for a successful medical school, the object 
 of which is to train good practical working physicians and 
 surgeons. The teaching staff of the Medical Faculty must 
 of necessity be almost all engaged in practice, and, indeed, 
 it would be unfortunate for their students if they were 
 merely theoretical teachers. Let me recapitulate my 
 point: the Medical Faculty is essentially a technical 
 Faculty ; the hospital is its workshop. 
 
 In England, of recent years, schools of engineering 
 have been attached to the Universities. Abroad and in 
 America they are separate establishments, and are some- 
 times attached to large engineering works, where the 
 pupils pursue their theoretical and practical studies 
 together, taking the former in the morning, the latter in 
 the afternoon. Here again the subject is a professional 
 one. The object of the student is to become a practical 
 engineer, and all his work is necessarily directed to that 
 end. Like other workers in different fields, his aim is the 
 
THE FUNCTIONS OF A UNIVERSITY 231 
 
 acquisition and utilisation of 'power/ but in his case it is 
 his object to direct mechanical and electrical power so as 
 to add to the convenience of the public. A machine is an 
 instrument for converting heat or electrical energy into 
 what is termed ' kinetic energy,' and it is with the laws 
 and modes of this conversion that he has to deal. Such 
 abstract sciences as chemistry, physics, and geology, 
 therefore, are studied as means to an end ; not for their 
 own sakes. They afford him a glimpse of the principles 
 on which his engineering practice is based ; and mathe- 
 matics is essential in order that he may be able to apply 
 physical principles to the practical problems of his pro- 
 fession. 
 
 We see, then, that a University, as it at present exists, 
 provides, or may provide, technical instruction for theo- 
 logians, for lawyers, for medical men, and for engineers. 
 It is, in fact, an advanced technical school for these 
 subjects. 
 
 But it is more, and I believe that its chief function lies 
 in the kind of work which I shall attempt now to describe. 
 The German Universities possess what they term a 
 ' Philosophical Faculty ' ; and this phrase is to be accepted 
 in the derivational meaning of the word a faculty 
 which loves wisdom or learning. The watchword of the 
 members of this faculty is Research; the searching out 
 the secrets of Nature, to use a current phrase ; or the 
 attempt to create new knowledge. The whole machinery 
 of the Philosophical Faculty is devised to achieve this 
 end ; the selection of the teachers, the equipment of the 
 laboratories and libraries, the awarding of the degrees. 
 
 What are the advantages of research ? Much is heard 
 nowadays regarding the necessity of state provision for 
 its encouragement, and the Government places at the 
 disposal of the Royal Society a sum of no less than 4000 
 a year, which is distributed in the form of grants to 
 
232 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 applicants who are deemed suitable by committees 
 appointed to consider their claims to assistance. 
 
 There are two views regarding the advantage of research 
 which have been held. The first of these may be termed 
 the utilitarian view. You all know the tale of the man 
 of science who was asked the use of research, and who 
 parried with the question What is the use of a baby ? 
 Well, I imagine that one school of political economists 
 would oppose the practice of child-murder on the ground 
 that potentially valuable property was being destroyed. 
 These persons would probably not be those who stood to 
 the baby in a parental relation. Nor are the most suc- 
 cessful investigators those who pursue their inquiries with 
 the hope of profit, but for the love of them. It is, how- 
 ever, a good thing, I believe, that the profanum vulyus 
 should hold the view that research is remunerative to the 
 public as some forms of it undoubtedly are. 
 
 The second view may be termed the philosophical one. 
 It is one held by lovers of wisdom in all its various forms. 
 It explains itself, for the human race is differentiated 
 from the lower animals by the desire which it has to know 
 ' why.' You may have noticed, as I have, that one of the 
 first words uttered by that profound philosopher, a small 
 child, is ' why ? ' Indeed it becomes wearisome by its 
 iteration. We are the superiors of the brutes in that we 
 can hand down our knowledge. It may be that some 
 animals also seek for knowledge ; but at best, it is of use 
 to themselves alone; they cannot transmit it to their 
 posterity, except possibly by way of hereditary faculties. 
 W T e, on the contrary, can write and read ; and this places 
 us, if we like, in possession of the accumulated wisdom of 
 the ages. 
 
 Now the most important function, I hold, of a Uni- 
 versity is to attempt to answer that question ' why ? ' 
 The ancients tried to do so; but they had not learned 
 
THE FUNCTIONS OF A UNIVERSITY 233 
 
 that its answer must be preceded by the answer to the 
 question ' how ? ' and that in most cases indeed in all 
 we must learn to be contented with the answer to ' how ? ' 
 The better we can tell how things are, the more nearly 
 shall we be able to say why they are. 
 
 Such a question is applicable to all kinds of subjects : 
 to what our forerunners on this earth did ; how they 
 lived : if we go even further back, what preceded them on 
 the earth. The history of these inquiries is the function 
 of geology, palaeontology, and palseontological botany ; it 
 is continued through archseology, Egyptian and Assyrian, 
 Greek and Roman ; it evolves into history, and lights are 
 thrown on it by languages and philology; it dovetails 
 with literature and economics. In all these, research is 
 possible; and a University should be equipped for the 
 successful prosecution of inquiries in all such branches. 
 
 Another class of inquiries relates to what we think and 
 how we reason ; and here we have philosophy and logic; 
 A different branch of the same inquiry leads us to mathe- 
 matics, which deals with spatial and numerical concepts 
 of the human mind, geometry and algebra. By an easy 
 transition we have the natural sciences ; those less closely 
 connected with ourselves as persons, but intimately related 
 to our surroundings. Zoology and botany, anatomy, 
 physiology and pathology deal with living organisms as 
 structural machines ; and they are based on physics and 
 chemistry, which are themselves dependent on mathe- 
 matics. 
 
 Such inquiries are worth making for their own sakes. 
 They interest a large part of the human race ; and not to 
 feel interested in them is to lack intelligence. The man 
 who is content to live from day to day, glad if each day 
 will but produce him food to eat and a roof to sleep under, 
 is but little removed from an uncivilised being. For the 
 test of civilisation is prevision ; care to look forward ; to 
 
234 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 provide for to-morrow ; the morrow of the race, as well as 
 the morrow of the individual ; and he who looks furthest 
 ahead is best able to cope with Nature, and to conquer 
 her. 
 
 The investigation of the unknown is to gather experience 
 from those who have lived before us, and to secure know- 
 ledge for ourselves and for those who will succeed us. I 
 see, however, that I am insensibly taking a utilitarian 
 view; I by no means wish to exclude it, but the chief 
 purpose of research must be the acquisition of knowledge, 
 and the second its utilisation. 
 
 I will try to explain why this is so, and here you must 
 forgive me if I cite well-known and oft- quo ted instances. 
 
 If attempts were made to discover only useful know- 
 ledge (and by useful I accept the vulgar definition of 
 profitable, i.e. knowledge which can be directly trans- 
 muted into its money equivalent) these attempts would, 
 in many, if not in most cases, fail of their object. I do 
 not say that once a principle has been proved, and a 
 practical application is to be made of it, that the working 
 out of the details is not necessary. But that is best done 
 by the practical man, be he the parson, the doctor, the 
 engineer, the technical electrician, or the chemist, and 
 best of all on a fairly large scale. If, however, the prac- 
 tical end be always kept in view, the chances are that 
 there will be no advance in principles. Indeed, what we 
 investigators wish to be able to do, and what in many 
 cases we can do, although perhaps very imperfectly, is to 
 prophesy, to foretell what a given combination of circum- 
 stances will produce. The desire is founded on a belief 
 in the uniformity of Nature ; on the conviction that what 
 has been will again be, should the original conditions be 
 reproduced. By studying the consequences of varying 
 the conditions our knowledge is extended; indeed it is 
 sometimes possible to go so far as to predict what will 
 
THE FUNCTIONS OF A UNIVERSITY 235 
 
 happen under conditions, all of which have never before 
 been seen to be present together. 
 
 When Faraday discovered the fact that if a magnet 
 is made to approach a coil of wire, an electric current is 
 induced in that wire, he made a discovery which at the 
 time was of only scientific interest. That discovery has 
 resulted in electric light, electric traction, and the utilisa- 
 tion of electricity as a motive power ; the development of 
 a means of transmitting energy, of which we have by no 
 means seen the end; nay, we are even now only at its 
 inception, so great must the advance in its utilisation 
 ultimately become. 
 
 When Hofmann set Perkin as a young student to 
 investigate the products of oxidation of the base aniline, 
 produced by him from coal-tar, it would have been 
 impossible to have predicted that one manufactory alone 
 would possess nearly 400 large buildings and employ 
 5000 workmen, living in its own town of 25,000 inhabi- 
 tants, all of which is devoted to the manufacture of colours 
 from aniline and other coal-tar products. In this work 
 alone at least 350 chemists are employed, most of whom 
 have had a university training. 
 
 Schonbein, a Swiss schoolmaster, interested in chemistry, 
 was struck by the action of nitric acid on paper and 
 cotton. He would have been astounded if he had been 
 told that his experiments would have resulted in the 
 employment of his nitrocelluloses in colossal quantity for 
 blasting, and for ordnance of all kinds, from the 90- ton 
 gun to the fowling-piece. 
 
 But discoveries such as these, which lead directly to 
 practical results, are yet far inferior in importance to 
 others in which a general principle is involved. Joule 
 and Robert Mayer, who proved the equivalence of heat 
 and work, have had far more influence on succeeding ages 
 than even the discoverers above mentioned, for they have 
 
236 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 imbued a multitude of minds with a correct understanding 
 of the nature of energy, and the possibility of converting 
 it economically into that form in which it is most directly 
 useful for the purpose in view. They have laid the basis 
 of reasoning for machines ; and it is on machines, instru- 
 ments for converting unavailable into available energy, 
 that the prosperity of the human race depends. 
 
 You will see from these instances that it is in reality 
 c philosophy ' or a love of wisdom which, after all, is most 
 to be sought after. Like virtue, it is its own reward ; and 
 as we all hope is the case with virtue too, it brings other 
 rewards in its train; not, be it remarked, always to the 
 philosopher, but to the race. Virtue, pursued with the 
 direct object of gain, is a poor thing; indeed, it can 
 hardly be termed virtue, if it is dimmed by a motive. 
 So philosophy, if followed after for profit, loses its 
 meaning. 
 
 But I have omitted to mention another motive which 
 makes for research ; it is a love of pleasure. I can 
 conceive no pleasure greater than that of the poet the 
 maker who wreathes beautiful thoughts with beautiful 
 words; but next to this, I would place the pleasure of 
 discovery, in whatever sphere it be made. It is a pleasure 
 not merely to the discoverer, but to all who can follow the 
 train of his reasoning. And after all, the pleasure of the 
 human race, or of the thinking portion of it, counts for a 
 good deal in this life of ours. 
 
 To return: attempts at research, guided by purely 
 utilitarian motives, generally fail in their object, or at 
 least are not likely to be so productive as research without 
 ulterior motive. I am strengthened in this conclusion by 
 the verdict of an eminent German who has himself put 
 the principle into practice ; who after following out a 
 purely theoretical line of experiment, which at first 
 appeared remote from profit, has been rewarded by its 
 
THE FUNCTIONS OF A UNIVERSITY 237 
 
 remunerative utilisation. He remarked, incidentally, that 
 the professors in Polytechnika (what we should term 
 technical colleges, intended to prepare young men for the 
 professions of engineering and technical chemistry) were 
 less known for their influence on industry than University 
 professors. The aim is different in the two cases; the 
 Polytechnika train men for a profession ; the Philosophical 
 Faculty of a German University aims at imparting a love 
 of knowledge ; and as a matter of fact the latter pay in 
 their influence on the prosperity of the nation better than 
 the former. And this brings me to the fundamental 
 premiss of my Oration. It is this : That the best prepara- 
 tion for success in any calling is the training of the student 
 in methods of research. This should be the goal to be 
 clearly kept in view by all teachers in the Philosophical 
 Faculties of Universities. They should teach with this 
 object: to awaken in each of their students a love of his 
 subject, and a consciousness that if he persevere, he, too, 
 will be able to extend its bounds. 
 
 Of course it is necessary for the student to learn, so far 
 as is possible, what has already been done. I would not 
 urge that a young man should not master, or at all events 
 study, a great deal of what has already been discovered, 
 before he attempts to soar on his own wings. But there 
 is all the difference in the world between the point of 
 view of the student who reads in order to qualify for 
 an examination, or to gain a prize or a scholarship, 
 and the student who reads because he knows that 
 thus he will acquire knowledge which may be used 
 as a basis of new knowledge. It is that spirit in 
 which our Universities in England are so lamentably 
 deficient; it is that spirit which has contributed to 
 the success of the Teutonic nations, and which is 
 beginning to influence the United States. For this con- 
 dition of things our examinational system is largely to 
 
238 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 blame ; originally started to remedy the abuses of our Civil 
 Service, it has eaten into the vitals of our educational 
 system like a canker; and it is fostered by the farther 
 abuse of awarding scholarships as the results of examina- 
 tions. The pauperisation of the richer classes is a crying 
 evil; it must some day be cured. Let scholarships be 
 awarded to those who need them ; not to those whose 
 fathers can well afford to pay for the education of their 
 children. ' Pot-hunting ' and Philosophy have absolutely 
 nothing in common. 
 
 There are some who hold that the time of an investi- 
 gator is wasted in teaching the elements of his subject. I 
 am not one of those who believe this doctrine, and for two 
 reasons : first, it is more difficult to teach the elements 
 of a subject than the more advanced branches ; one learns 
 the tricks of the trade by long practice ; and the tricks of 
 this trade consist in the easy and orderly presentment of 
 ideas. And it is the universal experience that senior 
 students gain more good from instruction in advanced 
 subjects by demonstrators than juniors would in elementary 
 subjects. For the senior student makes allowances ; and 
 the keenness and interest of the young instructor awakens 
 his interest. Second, from the teachers' point of view, it 
 is always well to be obliged to go back on fundamentals. 
 One is too apt, without the duty of delivering elementary 
 lectures, to take these fundamentals for granted ; whereas, 
 if they are recapitulated every year, the light of other 
 knowledge is brought to bear on them, and they are given 
 their true proportion; indeed, ideas occur which often 
 suggest lines of research. It is really the simplest things 
 which we know least of; the atomic theory; the true 
 nature of elasticity; the cause of the ascent of sap in 
 plants; the mechanism of exchange in respiration and 
 digestion; all these lie at the base of their respective 
 sciences, and all could bear much elucidation. I believe 
 
THE FUNCTIONS OF A UNIVERSITY 239 
 
 therefore, that it is conducive to the furtherance of know- 
 ledge that the investigator should be actively engaged in 
 teaching. But he should always keep in view the fact 
 that his pupils should themselves learn how to investi- 
 gate ; and he should endeavour to inculcate that spirit in 
 them. 
 
 It follows that the teachers in the Philosophical Faculty 
 should be selected only from those who are themselves 
 contributing to the advancement of knowledge ; for if they 
 have not the spirit of research in them how shall they 
 instil it into others ? It is our carelessness in this respect 
 (I do not speak of University College, which has always 
 been guided by these principles, but of our country as a 
 whole) which has made us so backward as compared with 
 some other nations. It is this which has made the vast 
 majority of our statesmen so careless, because so ignorant, 
 of the whole frame of mind of the philosopher ; and which 
 has made it possible for men high in the political estima- 
 tion of their countrymen to misconceive the functions 
 of a University. It is true that one of these functions of a 
 University is to ' train men and women fit for the manifold 
 requirements of the Empire ' ; that we should all heartily 
 acknowledge ; but no man who has any claim to university 
 culture can possibly be contented if the University does 
 not annually produce much work of research. It is its 
 chief excuse for existence ; a University which does not 
 increase knowledge is no University ; it may be a technical 
 school ; it may be an examining board ; it may be a 
 coaching establishment ; but it has no claim to the name 
 University. The best way of fitting young men for the 
 manifold requirements of the Empire is to give them the 
 power of advancing knowledge. 
 
 It may be said that many persons are incapable of 
 exhibiting originality. I doubt it. There are many 
 degrees of originality, as there are many degrees of 
 
240 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 rhyming, from the writer of doggerel to the poet, or many 
 degrees of musical ear, from the man who knows two 
 tunes, the tune of ' God save the King ' and the other 
 tune, to the accomplished musician. But in almost all 
 cases, if caught young, the human being can be trained, 
 more or less ; and, as a matter of fact, natural selection 
 plays its part. Those young men and women who have 
 no natural aptitude for such work and they are usually 
 known by the lack of interest which they take in it do 
 not come to the University. My experience is that the 
 majority, or at least a fair percentage of those who do 
 come, possess germs of the faculty of originating, germs 
 capable of development, in many instances, to a very high 
 degree. It is such persons who are of most value to the 
 country ; it is from them that advance in literature and 
 in science is to be expected ; and many of them will con- 
 tribute to the commercial prosperity of the country. We 
 hear much nowadays of technical education ; huge sums 
 of money are being annually expended on the scrappy 
 scientific education in evening classes of men who have 
 passed a hard day in manual labour, men who lack the 
 previous training necessary to enable them to profit by 
 such instruction. It may be that it is desirable to pro- 
 vide such intellectual relaxation ; I even grant that such 
 means may gradually raise the intellectual level of the 
 country ; but the investment of money in promoting such 
 schemes is not the one likely to bear the most immediate 
 and remunerative fruit. The Universities should be the 
 technical schools ; for a man who has learned to investi- 
 gate can bring his talents to bear on any subject brought 
 under his notice, and it is on the advance, and not the 
 mere dissemination of knowledge, that the prosperity of 
 a country depends. To learn to investigate requires a 
 long and a hard apprenticeship ; the power cannot be 
 acquired by an odd hour spent now and again ; it is as 
 
THE FUNCTIONS OF A UNIVERSITY 241 
 
 difficult to become a successful investigator as a successful 
 barrister or doctor, and it requires at least as hard appli- 
 cation and as long a period of study. 
 
 I do not believe that it is possible for young men or 
 women to devote sufficient time during the evening to 
 such work. Those who devote their evening hours to 
 study and investigation do not bring fresh brains to bear 
 on the subject; they are already fatigued by a long day's 
 work; and, moreover, it is the custom in most of the 
 colleges which have evening classes to insist upon their 
 teachers doing a certain share of day work ; they, too, are 
 not in a fit state to direct the work of their pupils nor to 
 make suggestions as to the best method of carrying it out. 
 Moreover, the official evening class is from seven to ten 
 o'clock, and for investigation in science a spell of three 
 hours at a time is barely sufficient to carry out success- 
 fully the end in view ; indeed, an eight hours' day might 
 profitably be lengthened into a twelve hours' day, as it not 
 infrequently is. It is heartrending in the middle of some 
 important experiment to be obliged to close and postpone 
 it till a future occasion, when much of the work must 
 necessarily be done over again. 
 
 These are some of the reasons why I doubt whether 
 University education, in the Philosophical Faculty at 
 least, can be successfully given by means of evening 
 classes. 
 
 Although my work has lain almost entirely in the 
 domain of science, I should be the last man not to do my 
 best to encourage research in the sphere of what is gener- 
 ally called ' arts.' In Germany of recent years a kind of 
 institution has sprung up which is termed a Seminar. 
 The word may be translated a ' literary laboratory.' I will 
 endeavour to give a short sketch on the way in which 
 these literary laboratories are conducted. After the 
 student has attended a course of lectures on the subjects 
 
 Q 
 
242 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 to which he intends to devote himself, and is ripe for 
 research, he enters a Seminar, in which he is provided 
 with a library, paper, pens and ink, and a subject. The 
 method of using the library is pointed out to him, and he 
 is told to read books which bear on the particular subject 
 in question ; he is made to collate the information which 
 he gains by reading, and to elaborate the subject which 
 is given him. Naturally his first efforts must be crude, but 
 ce n'est que le premier pas qui cotite. It probably costs him 
 blame at the hands of his instructor ; after a few unsuc- 
 cessful efforts, however, if he has any talent for the par- 
 ticular investigation to which he has devoted himself, 
 his efforts improve and at last he produces something 
 respectable enough to merit publication. Thus he is 
 exposed to the criticism of those best competent to judge, 
 and he is launched in what may be a career in Historical, 
 Literary, or Economic research. 
 
 Such a Seminar is carried on in philological and 
 linguistic studies, in problems of economy involving 
 statistics, in problems of law involving judicial decision, 
 and of history in which the relations between the develop- 
 ment of the various phases in the progress of nations is 
 traced. The system is borrowed from the well-known 
 plan of instruction in a physical or chemical laboratory. 
 Experiments are made in literary style. These experi- 
 ments are subjected to the criticism of the teacher, and 
 thus the investigator is trained. But it may be objected 
 that the youths who frequent our Universities have not a 
 sufficient knowledge of facts connected with such subjects 
 to be ^capable of at once entering on a training of this 
 kind. That may be so ; if it is the case, our schools must 
 look to it that they provide sufficient training. Even 
 under present circumstances, however, I do not think I 
 am mistaken in supposing that a young man or woman 
 who enters a University at the age of eighteen years with 
 
THE FUNCTIONS OF A UNIYEESITY 243 
 
 the intention of spending three years in literary or his- 
 torical studies will not at the end of the second year be 
 more benefited by a course at the Seminar, even though it 
 should result in no permanent addition to literature or 
 history, than if he were to spend his time in mere assimi- 
 lation. It is not the act of gaining knowledge which 
 profits, it is the power of using it, and while in order to 
 use knowledge it is necessary to gain it, yet a training in 
 the method of using knowledge is much more important 
 and profitable than a training in the method of gaining 
 it. I do not know whether there exists in this country a 
 single example of the continental Seminar ; there was some 
 talk of founding such a literary laboratory in University 
 College, but, as usual, the attempt was frustrated by a 
 lack of funds ; the attempt would also have been frustrated 
 by the requirements of the present system of examination 
 in the University of London ; but there is, fortunately, 
 good hope of changing that system and of developing the 
 minds of students on those lines which have proved so 
 fruitful where they have been systematically followed. 1 
 
 There is one subject, of which the votaries are so few, 
 that it is difficult to treat in the same manner as those 
 literary and scientific subjects of which I have been speak- 
 ing; that subject is mathematics. While many persons 
 have a certain amount of mathematical ability which 
 they cultivate as a means to an end, those who are born 
 mathematicians are as few as those who are born 
 musicians. I have had the privilege of discussing this 
 question with one of the foremost mathematicians of 
 Europe Professor Klein of Gottingen. He tells me that 
 while he is content for the most part to treat mathematics 
 as a technical study, imparting to his pupils so much as is 
 necessary for them to use it easily as an instrument, he 
 
 1 Several Seminars have now been started at University College 
 (Sept. 1908). 
 
244 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 discourages young men, unless they are especially 
 endowed by Nature, from pursuing the study of mathe- 
 matics with the object of cultivating a gift for that 
 subject. Especially gifted men occasionally turn up, and 
 those who possess mathematical insight are able to profit 
 by the instruction of the professor in developing some 
 special branch of the subject. Mathematical problems, 
 he tells me, are numerous, but they demand such an ex- 
 tensive knowledge of what has already been done that 
 very few persons who do not devote their lives to the sub- 
 ject are able to cope with them, and it is only those who 
 are born with a mathematical gift who can afford to 
 devote their lives to mathematics, for the standard is high, 
 and the prizes are few. 
 
 Many, I suppose, who are at present listening to me 
 would be disappointed were I not to refer to the functions 
 of a University with reference to examinations. A long 
 course of training, lasting now for the best part of seventy 
 years, has convinced the population of London that the 
 chief function of a University is to examine. Believe me, 
 the examination should play only a secondary part in the 
 work of a University. It is necessary to test the acquire- 
 ments of the students whom the teachers have under 
 their charge, but the examination should play an entirely 
 subordinate part. To be successful in examinations is 
 unfortunately too often the goal which the young student 
 aims at, but it is one which all philosophical teachers 
 deprecate. To infuse into his pupils a love of the sub- 
 ject which both are at the same time teaching and learn- 
 ing, is the chief object of an enthusiastic teacher; there 
 should be an atmosphere of the subject surrounding them 
 an umbra perhaps I should call it an aura; for it 
 should exert no depressing influence upon them. The 
 object of both classes of students (for I count the teacher 
 a student) should be to do their best to increase know- 
 
THE FUNCTIONS OF A UNIVERSITY 245 
 
 ledge of the subject on which they are engaged. That 
 this is possible, many teachers can testify to by experi- 
 ence; and it is the chief lesson learned by a sojourn in a 
 German laboratory. Where each student is himself 
 engaged in research, interest is taken by the students in 
 each others' work; numerous discussions are raised 
 regarding each questionable point; and the combined 
 intelligence of the whole laboratory is focussed on the 
 elucidation of some difficult problem. There is nothing 
 more painful to witness than a dull and decorous labora- 
 tory, where each student keeps to his own bench, does not 
 communicate with his fellow-students, does not take an 
 interest in their work, and expects them to manifest no 
 interest in his. It is only by friction that heat can be 
 produced, and heat, by increasing the frequency of 
 vibration, results, as we know, in light. 
 
 The student should look forward to his examination 
 not as a solemn ordeal which he is compelled to go 
 through with the prospect of a degree should he be suc- 
 cessful, but as a means of showing his teacher and his 
 fellows how much he has profited by the work which he 
 has done ; those who pursue knowledge in this spirit and 
 those, be it remarked, who examine in this spirit will look 
 forward to examination with no apprehension ; not, per- 
 haps, with joy, for after all it is a bore to be examined 
 and perhaps a still greater bore to examine, but it is a 
 necessary step for the student in gaining self-assurance 
 and the conviction of having profited by his exertions ; 
 and for the teacher, as a means of insuring that his 
 instruction has not been profitless to his student. In this 
 connection I cannot refrain from remarking, that that 
 genius for competition which has over-ridden our nation 
 of England, appears to me to be misplaced. Far too 
 much is thought of the top man ; very likely the second 
 or even the tenth, or it may be the fiftieth has a firmer 
 
246 ESSAYS BIOGRAPHICAL AND CHEMICAL 
 
 grasp of his subject, and in the long-run would display 
 more talent. Let us take comfort, however, in the 
 thought, that the day of examinations, for the sake of 
 examinations, is approaching an end. 
 
 It may surprise many to learn that the suggestion that 
 in England teachers do not usually examine their own 
 pupils for degrees, is, abroad, received in a spirit of sur- 
 prise not unmixed with incredulity. Americans and 
 Germans to whom I have mentioned this state of matters, 
 cannot realise that the teacher is not considered fit to be 
 trusted to examine his own pupils, and, singular to state, 
 they maintain that no one else can possibly do so with 
 any attempt at fairness ; it appears to them, as it appears 
 to me, an altogether untenable position to hold that a 
 man selected to fill an important professorship, after many 
 years' trial in a junior position, should be suspected of 
 such (shall I say) ambiguous ideas regarding common 
 honesty, that he will always arbitrate unfairly in favour of 
 his own pupils. Such a supposition is an insult to the 
 professor ; and the exclusion of the teacher elevates 
 examination to the position of a fetish ; it is that, together 
 with the spirit of emulation and competition, which has 
 done so much to ruin our English education. The idea of 
 competitive examination is so ingrained in the minds of 
 Englishmen, that it is difficult for them to realise that 
 the object of a University is not primarily to examine its 
 pupils, but to teach them to teach themselves ; and also 
 they have still to acquire the conviction that students 
 should be found not merely among the alumni of the 
 University but also among all members of the staff. The 
 spirit which should prevail with us should be the spirit 
 of gaining knowledge gaining knowledge not for the 
 satisfaction of one's own sense of acquisitiveness, but in 
 order to be able to increase the sum- total of what is 
 known. All should work together, senior and junior staff, 
 
THE FUNCTIONS OF A UNIVERSITY 247 
 
 graduates and undergraduates, in order to diminish man's 
 ignorance. 
 
 To sum up. As it exists at present, a University is a 
 technical school for theology, law, medicine, and engineer- 
 ing. It ought to be also a place for the advancement of 
 knowledge, for the training of philosophers, of those who 
 love wisdom for its own sake ; and while as a technical 
 school it exercises a useful function in preparing many 
 men and women for their calling in life, its philosophical 
 faculty should impart to those who enter its halls that 
 faculty of increasing knowledge which cannot fail to be 
 profitable not only to the intellect of the nation, but also 
 to its industrial prosperity. I regard this as the chief 
 function of a University. 
 
 Yx 5 
 
 OF THE 
 
 UNIVERSITY 
 
 OF 
 
 *Urr- 
 
 Printed by T. and A. CONSTABLE, Printers to His Majesty 
 at the Edinburgh University Press 
 
A 
 
THE LAST DATE f 
 
 MAV 5 
 
 APR 15 
 
 4 1940 
 
 OCT 
 OCT 
 
 1943 
 
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 LD 2lA-45m-9,'67 
 (H5067slO)476B 
 
 General Library 
 
 University of California 
 
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 UNIVERSITY OF CALIFORNIA LIBRARY