A DISCOURSE MATHEMATICAL ON THE VARIATION OF THE MAGNETICAL Needle. Together with Its admirable Diminution lately discovered. By Henry Gellibrand Professor of Astronomy in Gresham College.  Veniet tempus, quo ista quae nunc latent, in lucem dies extrahat, et longioris aevi diligentia. Sen. Nat: Quaest. lib. 7. cap. 25. 
LONDON, Printed by William jones, dwelling in Red-crosse-street. 1635.   

A DISCOURSE MATHEMATICAL on the variation of the Magnetical Needle.  
TO write an Encomiastique of the Magnet is not my intention; the bold & confident attempts of Seamen, through those hidden paths of the vast Ocean, to all navigable parts of the earth, will spare me the labour; neither will these few lines permit me to speak of all Magnetical qualities, they that list may have recourse for their satisfaction herein, to that most learned work (admired by all Foreiners) long ago penned by Mr. Dr. Gilbert our countryman, sometimes Physician to that Renowned Lady our late Queen. That which I here principally aim at, is the deflection of the Needle from the Terrestrial Meridian, together with that abstruse and admirable variation of the Variation, lately discovered to the world.  
The Variation than is the deflection of the Magnetical Meridian from the Terrestrial, the Horizon determining its Quantity and Quality. These Meridian's sometimes are coincident, and in such places there can be no Variation▪ Sometimes again they are different, and then that Hemispere wherein either extremity of the Needle lies, denominates its Quality, for if it be the Eastern Hemispere, it is called Easterly variation, if the western, westerly. And the Horizon supposed (as all great Circles are) to be divided into 360 parts, & each part subdivided into Centesmes or Millesmes, defines the Quantity as 10, 20, 30, etc. parts of variation.  
For our more distinct proceeding (and to give some satisfaction to those that are not altogether Mathematical) it will not be impertinent to our present purpose to give some probable Reason for this variation or swarving of the Needle from the meridians of most places.  
Take a vigorous Magnet, convert it into a Spherical Body, and having found its Poles, delineat the same with Meridian's, the Equinoctial, and Parallels.  
Then take a fine sowing Needle, and applying it to the intersection of a Meridian and the Equinoctial, it will be found precisely to point out the Poles of the stone; and if the Needle be moved towards either Pole, according to its own direction, it will trace out a Circle over the said Magnetic Pole. But if this Spherical Magnet shall have a part of it excavated, as admit about the forty fifth Parallel, and forty fifth Meridian or degree of longitude, the Needle moved forwards from the foresaid intersection, as soon as it shall draw near to the limb of this excavation, will forthwith leave its former position, as lying in the plane of the prime meridian, and incline to the other solid side, not respecting at all the aforesaid Poles: and this deflection we call the variation of the Needle: And the greater will this variation be, the nearer it approacheth to the Poles. For whereas before the excavation each side being a like potent, 
Which may be some cause of those sudden and exorbitant variations in the Nortwest and other Northern & Southern parts of the Earth.  the Needle like an upright and indifferent Arbiter inclined to neither part; after the excavation it will convert itself to the more solid side, rejecting the imperfect and defective, and so much the more powerfully, by how much the other side shall be found to have lost more of its Magnetic vigorous substance.  
The like will fall out if the Needle be so placed, as that it shall bisect the excavated part, for than will it acurately point out the true Poles of the stone formerly found, but suddenly swerve from them after any little dislocation, strongly applying itself to the more solid side.  
As it is with this little, so likewise with the greater Magnet the Earth, whose solid magnetic parts are great Continents, the defective and excavated, the deep and vast channel of the Sea. For if there were observations made in the mid way between the Easterly Coast of China and this western of Europe, it is very probable there would be found no variation at all, the Terrestrial and Magnetical Meridian's being congruall; but if we shall incline to either side, as admit to the westward, the Needle will in like manner move itself to the Eastern Continent, as the more prevalent side, the channel of the Sea being a part deficient of the Spherical Body of the Earth, and the Needle finding no encouragement to apply itself there to.  
And so likewise for the Ocean, which palliates the imperfect parts of the Earth, it is evident, that if the Needle shall equally divide the Marine distance between two continents, there will be found no variation, as having both the Meridian's united, the Needle equally disposing itself to either Continent. But if we shall swerve from this mediety, it will preponderate with the next continent.  
For the evidence of the truth hereof, let a man examaine generally the variations of our most expert Seamen, (a Catalogue whereof we have annexed to that accurate work of Mr. Wright in his detection and conection of errors in Navigation) (although by reason of the diversities of the sets of their Compasses and oftentimes unapt handling of their instruments, they very seldom concur) observed in the Atlantic Ocean, from the Equator unto the parts of Norway, all along the East Coast from the Meridian of the Azores, as far North as hath been discovered, and he shall find the ordinary practice to testify the truth hereof. As also after the same manner from the Equator southward, unto the straits of Magellan, and all along the back parts of America in the South Sea, and on the East Coast unto the Cape of Bona Speranza, and he shall perceive the like agreement; But in failing from the aforesaid Cape further Eastward, that sometime they do find it otherwise, the cause proceedeth from the different situation of the South Continent hitherto undiscovered. And whereas in the Atlantic Ocean about 135 leagues from the Lands of Corues and Flores to the westward, 
Mr. john Wells.  there hath been found by an able Artist no variation at all, it is a manifest argument, that the Place is equidistant from the European or African continents and the American: And as we approach to either Continent, so shall we find the Needle praepotent in its conversion; from whence the variation shall receive its denomination.  
Therefore its absurd for Seamen to touch their Compasses with the allowance of the variation of any particular place, considering this variation is perpetually variable according to the ships motion.  
And moreover it's absolutely necessary for that Seaman who sails by his Compass, continually to search the variation, that so by the Prosthaphaereticall application thereof, the true point of the compass (which is his principal Mercurialist) may be rectified.  
And this artifice may be performed by the assistance of the Planets or fixed Stars, and that either without or with their Altitudes. I shall not need to exemplify all varieties, as having elsewhere copiously and demonstratively delivered the same. I think it only convenient to touch lightly at one or two, and such as best conduce to our present purpose.  
And first without an Altitude. Find two fixed Stars of equal right Ascension, and holding up a thread and plummet, observe when the thread bisects them (for that is the exact Meridian of the place) and at that instant apply the Compass to them; if the Needle precisely respect them, there is no variation; if not, then is the difference, the variation inquired; and that part of the Horizon to which it inclines, (always accounting from the same intersection of the Horizon and Meridian) claims it.  
It may likewise be performed by the Amplitude Ortive or Occiduall of the Sun, and as well by night as by day, by the rest of the Planets or fixed Stars, having only their declinations and the Latitude of the places, either Geometrically by an Analemme, or Arithmetically by the help of the Canon of Triangles, for the ordinary terms of the proportion run thus.  
As the Sine compliment of the Latitude, is to the Radius, So the Sine of the declination, to the Sine of the Amplitude. Turning therefore the Compass to the Sun or Stars, the difference of the Arcs is the variation inquired. Or by knowing the time of the Sun's incidence into the Plane of the Prime vertical, after the like manner we may obtain our desires.  
But in these and some other ways, we are confined to a certain time: If therefore to the former requisits we shall add an Altitude, this Artifice may be performed at any convenient appearance of a Planet or Star, as we shall by and by show.  
And for the more easy and certain obtaining of the variation at Sea, I would advise the Seaman to extend or prolong the capital of his Needle, or fix some style on it, so that it may cut the Fly at right Angles, for then the Compass coverted to the Sun, this style will readily shadow out the Azimuth Magnetical, and comparing it with that of the Sun, he hath the variation near enough without any further labour or preparation.  
Thus hitherto (according to the Tenants of all our Magnetical Philosophers) we have supposed the variations of all particular places to continue one and the same: So that when a Seaman shall haply return to a place where formerly he found the same variation, he may hence conclude, he is in the same former Longitude. For it is the Assertion of Mr. Dr. Gilberts. Variatio v●…icuiusque Loci constans est, that is to say, the same place doth always retain the same variation. Neither hath this Assertion (for aught I ever heard) been questioned by any man. But most diligent magnetical observations have plainly offered violence to the same, and proved the contrary, namely that the variation is accompanied with a variation. For whereas in the year 1580 Mr. Burrows (a man of unquestionable abilities in the Mathematics) found the variation at Limhouse near London to be 11 gr. 15 min. or near one point of the Compass; In the year 1622 Mr. Gunter sometimes professor of Astronomy in Gresham College, found the variation in the same place to be but 6 gr. 13 min. And myself this present year 1634 with some friends had recourse to Dedpford (where Mr. Gunter had heretofore made the same observations with those at Limehouse) and found it not much to exceed 4 degrees.  
For the clearer manifestation of this truth, (because all men have not been furnished with or seen the fore said observations, I hold it necessary to transfer theirs hither, and subnect those which were lately made by myself with the assistance of some friends.  

Mr. Burrowes his observations made at Limehouse October. 16. 1580.  Before Noon. After Noon.  Elevation of the ☉ variation of the shadow from the North of the Needle to the westwards. Elevation of the ☉ variat: of the shadow from the North of the Needle to the Eastward variat. of the Needle from the Pole or Axis. Gr. Min. Gr. Min. Gr. Min. Gr. Min. Gr, Min. Sec. 17: 0 52, 35 17: 0 30: 0 11: 17, 30 18: 0 50 8 18: 0 27. 45 11. 11. 30 19: 0 47 30 19: 0 24. 30 11. 30, 0 20: 0 45 0 20: 0 22: 15 11, 22. 30 21: 0 42 15 21: 0 19 30 11. 22, 30 22: 0 38 0 22: 0 15: 30 11. 15. 0 23: 0 34 40 23: 0 12. 0 11. 20. 0 24: 0 29 35 24: 0 7: 0 11. 17, 0 25: 0 22 20 25: 0 0: 8 11. 14. 0    From N to W   
The way of finding the variation after this manner is easy to be conceived. A time being chosen when the Heavens were like to be unmasked for the whole day, the altitudes of the Sun were taken by him to each degree of a Quadrant both forenoon & Afternoon, from 17 to 25 gr. making nine several observations. And at every Altitude turning his Needle to the Sun, observed the degree and parts cut thereby. Then comparing the Magnetical Azimuthes made in the Forenoon, with those in the Afternoon answerable to the same Solar altitudes, the half of the difference is the variation. Thus at the altitude of 17 gr. in the Forenoon, the Needle cutting 52 gr. 35 min. and at the same altitude in the Afternoon 30 gr. 0 min: the difference is 22 gr. 35 min: the half whereof is 11 gr. 17 min: 30 Sec. the variation inquired.  
Before we proceed to other Observations it will be requisite we take a review of these, and after correction of some of the apparent Altitudes, call the Solar Azimuthes to the judicature of a Triangle.  
It is not unknown that about this time of Mr. Burrowes his observations the accurate and corrected tables of the Sun's motion were not published to the world, Neither the Angles of the Obliquity and Paralaxes of the Sun so truly determined. And as for the refraction (which insinuates itself in every Altitude not exceeding 45 degrees) being then in its infancy and a stranger to the world it was not called into the account, no not by the Ancients themselves, nor limited before that great Astronomer and honourable Dane Tyche Brahe opened the same way. If therefore we shall examine these Altitudes according to the late corrected grounds, we shall somewhat alter the variations of Mr. Burrowes, but so as that we shall not much differ from him, or suspect any great error in his work.  
These observations then of his, were made the 16 of October Anno 1580. And by Astronomical Calculation should begin about 9 ½ in the Morning, and end about 2 ⅓ in the Afternoon. Let us now make choice of the Magnetical Azimuthes answerable to the Altitudes of 20 gr. being the fourth observation. The true place of the Sun about this time correspondent to this Altitude according to the late Rud●lphins Tables, (with consideration to the difference of Meridian's and Equation of Time) is thus found after the Centesimall way with the connexion of our British Logarithmes, but with some alteration of the Anomalies  
Motion of the Apog. ☉ Middle motion of the Sun Sig. Gr. Sig. Gr. Epoch of Christ 2: 83455571829 9: 88667238532 years 1579 0: 270303979753 0: 111927414346 Month: Biss: 9 0: 00 128419571 9: 00672704358 Days 14. 0: 000007030268 0: 137990576119 Her. 21. Min. 9 0: 00000413028 0: 08686013944 Sum of the mot. 3: 53895414449 7: 47943947299 Motion of the Apogaum substracted 3: 53895414449 The middle Anomaly. 3: 294048532850 Our Tabular middle Anomaly 3: 29 00000 The difference of Anomalies 0: 0 40485 The logarithme whereof is 0. 6072976 The diff. of the Coaequated Anom. 1. 01729167 The logarithme whereof is 0: 0074454 The sum of the logarithmes 0: 6147430 To which there answers 04118538 which added to the tab: Coaeq: Anom. 3. 271763527 Gives the inquired coaeq: Anomaly 3. 275882065 To this the Apog: added 3. 5 3895414 Gives the Sun's place in ♏ 2 9777479 The declination whereof is 12548280 Whereunto adding a Quadrant 90000000 The sum is the ☉ dist. from the Pole 102548280  
And because we have made choice of the apparent Altitude of 20 gr. the Parallax (Kepler admitting little or none,) according to Tycho Brahe will be found Gr. 0047778 And the refraction 0075000 The difference is 0027222 Which substracted from the apparent Alt. 20000000 Gives the true Altitude of the ☉ 19972778 The compliment whereof is the distance  of the ☉ from the Zenith 70027222  
 Logarithmes PS. Dist of the ☉ from the Pale 10254789 00269391447 ZS. Compl. of the ☉ altitude 7002722 02061682627 ZP. compl. of the Latitude 3846667  Sum of the sides 21104178  The half sum 10552089 99838665722 Diff. of the Base and ½ sum. 297299 87148768587  189318508383 The log. of the sine of 169996 94659254191 The compliment 730004   
The double whereof is 1460008 the Angle inquired PZS. But the Magnet. Azim. is 1350000 namely the Angle CZS. The differ. is 110008 MZB the variation inquired, which converted into sexagesmes is 11 gr. 0 min, 0 Sec. Mr, Burrowes by the help of the afternoons observation making it 11. gr. 22 min. 30 sec. the difference being 0 gr. 22 min. 30 sec.  
Gr.  PS. dist. of the ☉ from the Pole 10261740  ZS. compl. of the ☉ Altitude 700272●  ZP. compl. of the Latitude 3846667  The sum of the sides 21●●●129 Logarithmes The half sum 10555564 00162066869 Dif. of the half sum & sides PS 293824 12902261021 ZS 3552842 97642558829 ZP 6708897 99643117219 The sum of the logarithmical sins 210350003938 Logarithmical tang: of half the Angle 105175001969 which found in the canon answereth to 73104441 the double whereof is the angle sought 146208882 PZS But the Magnetical Azim: is 157750000 CZS The difference is the variation 11541118 CZP.  
which converted into sexagesmes, is 11 gr. 32 min. 28: sec. And if with this we compare the morning variation, (which should have been the same with the afternoons) the difference will be 32 min: 28 sec: which may easily arise either from the Insufficiency or Fabric or gross handling of the Instruments. So that if we take the Arithmetical means, we may probably conclude the variation answerable to his time to be about 11 gr. 16 min: with which very near concurreth Dr. Gilbert, finding it 11 gr. 20 min.  
From these we proceed to Mr. Gunter's Observations, the Table whereof we have here inserted, as we find them in his mathematical works, where we see the variation not to exceed 6 gr. 13 min. His instruments were one Quadrant of three foot Radius for the Sun's Altitudes: His Needles were two, the one of six, the other of 10 Inches in length. The Sun's Azimuthes were found by calculation, and the Azimuthes Magnetical, taken off a horizontal Plane by a line of Chords, whose Semidiameter was twelve Inches.  

Mr. Gunters Observations made at Limehouse jun: 13 Anno 1622 after Noon.  Alt: ☉ Azim: Madge Azim: ☉ Variation. Gr. Min. Gr. Min. Gr. Min. Gr. Min. 19 0 82 2 75 52 6 10 18 5 80 50 74 44 6 6 17 34 80 0 74 6 5 54 17 0 79 15 73 20 5 55 16 18 78 12 72 32 5 40 16 0 77 50 72 10 5 40 10 10 71 2 64 49 6 13 0 52 70 12 64 25 5 47  
Thus have we proved that for the Interstice of 42 years, there hath been an evident diminution of five, degrees variation. I deny not the Artifice to be very nice and subtle, and that an error may unawares easily insinuate itself, which together with this great discrepance, moved some of us to be overhasty in casting an aspersion of error on Mr. Burrows observations, 
Mr. john Marr.  (though since upon no just grounds) till an acquaintance of ours, lately applying Mr. Gunter's own Needle to the side of the cubical Stone of his Majesty's Dial in White Hall garden, could not find the variation so great as 6 gr. 15 min: formerly found; whereupon resolving with some friends to make an experiment hereof, we went to Diepford the last year 1633 the day of the Sun's entrance into the summer Solstice, to the very same place where Mr. Gunter heretofore had made observation, and found it much less than five degrees; And afterwards calling into Question the Insufficiency of our Instruments, that all scruple might be quite taken away, we had recourse this present year 1634 joh. 12. stilo vet: to the same Garden of our learned and ingenuous friend Mr. john Welles, with a Quadrant of six foot Radius for solar Altitudes, continually rectified with great care, and a horizontal Quadrant of two foot Radius, for the determining of the Magnetical Azimuthes, exactly set to the Magnetical meridian, and in paralellisme to the Horizon; (otherwise great error might ensue) with two Needles of twelve Inches in length well touched with good Magnetts; And for the better satisfaction, took with us also the very same Needle wherewith Mr. Gunter made the foresaid observations, in length ten Inches; all three must, accurately respecting the same Magnetical Meridian as we then proved. And lest there might arise some diversity in the variation through the touches of several Stones, I caused the one Needle first touched by a very good Magnet, to be retouched by another as good if no better, and the same wherewith most of our zoea compastes are touched, and yet found no difference between them. And so june the 14. 1634▪ we made these following observations, where we found the variation not to exceed 4 gr. 10 min. as appeareth by the Table annexed.  
And because in the Resolutions of these obliquangular spherical Triangles for the Solar Azimuthes we have necessary use of the Latitude of the Place, the same we determine by the Sun's meridian Altitude to be 51 gr. 30 min. after this manner.  
 Gr. The apparent Altitude of the Sun 62: 0: 0 The Parallax of the Sun added 0: 1: 22 Therefore the Sun's true altitude 62: 1: 22 Sun's declination according to Tycho 23: 31▪ 22 Hence the Altitude of the Equinoctial 38: 30. 0 The compl. whereof is the height of the Pole 51. 30. 0  

Observations made at Diepford An. 
Testibus ac secus is D. Welles. Harrison. Marr. Butler. Ho●ton. Ho●knell.  1634 junij 12 before Noon  Alt: ☉ vera Azim. Madge Azim. ☉ variation Gr. Min. Gr. M. Gr. M, Gr. M. 44, 45. 106, 0 110 6 4. 6 46, 30, 109, 0 113 10 4 10 48. 31, 113, 0 117 1 4 1 50, 54, 118▪ 0 122, 8 4. 2 54, 24, 127. 0 ●30 55 3 5  

After Noon the same day.  Alt. ☉ vera Azi. Madge Azim. ☉ Variation Gr. Min. Gr: M. G. Mn. Gr, Min 44 37 114: 0 109. 53. 4: 7 40 48 108: 0 103, 50 4: 10 38 46 105. 0 100, 48 4. 12 36 43 102, 0 97. 56 4. 4 34 32 99, 0 95, 0 4: 0 32 10 96: 0 91. 55 4: 5  
These Concordant Observations can not produce a variation greater than 4 gr. 12 min. nor less than 3 gr. 55 min. the Arithmetical mean limiting it to 4 gr. and about 4 minutes.  
And for a further confirmation hereof (though moved upon no just reason to suspect these observations, being every way as cautelous in them as possible we could) as soon as the intermission from my public Exercise would permit, I caused the same instruments to be transported to Paul's Cray in Kent, distant from London SE and by S about 12 miles, where the fourth of july following (Fide Astronimica) I made the subsequent animadversions, hardly amounting to 4 degrees.  
The Latitude of the Place I find by the same large Quadrant to be 51 gr. 25 min. which thus I prove.  
 o i two july 21 the ☉ apparent meridian altit. was 56: 53: 0 The Suns parallex to be added 0, 1. 36 The sum is the Sun's true Altitude 56, 54, 36 The declination of the Sun subtracted 18, 19, 36 The Relic is the altitude of the equinoc. 38. 35. 0 The compl: whereof is the height of the Pole 51. 25, 0  

Observations made at Paul's Cray in Kent july: 4: 1634: After Noon.  vera alt. ☉ Azim: mag Azim: ☉ variatio Gr, Min: Gr, Min: Gr. Min: Gr: Min 40: 55. 111 30 107 30 4 0 40: 1 110 0 106 5 3 55 39: 41. 109 30 105 34 3 56 38: 42. 108 0 104 5 3 55 35: 32. 103 30 99 32 3 58 34. 49. 102 30 98 32 3 58 33, 41, 101 0 97 0 4 0 32. 57: 100 0 96 2 3 58 32: 9, 99 0 94 58 4 2 31, 25, 98 0 94 0 4 0 30: 39: 97 0 93 1 3 59 29: 29: 95 30 91 31 3 59 27, 51: 93 30 89 28 4 2  
It were needless having so many sufficient testimonies, to produce any more; one only observation made with circumspection being as good as one hundredth. So that its plain, the observations made in this place do all make the variation to fall near upon 4 degrees.  
Hence therefore we may conclude that for the space of 54 years (the difference of time between Mr. Burrowes and these last observations of ours) there hath been a sensible diminution of 7 degrees and better.  
If any affected with magnetical Philosophy shall yet desire to see an experiment made for their own particular satisfaction, where I may prevail, I would advise them to pitch a fair stone parallel to the Horizon there to rest immovable, and having a Needle of a convenient length strongly touched by a vigorous Magnet to draw a Magnetical Meridian thereby, and yearly to examine by the application of the same (well preserved from the air and rust, its greatest enemies) whether time will produce the like alteration.  
I will not here enter into a dispute concerning the cause of this sensible diminution, whether it may be imputed to the Magnet, or the Earth, or both. It is not unknown to the world, how the Greatest Masters of Astronomy, which this age hath afforded, for the more easy salving the apparent anomalar motions of the fixed and erratic celestial lights, and avoiding that supervacaneous furniture of the Ancients, do with all alacrity embrace that admirable Copernicean Hypothesis of the diurnal, Annual, & Secular motions of the earth, in so much as conferring with that Great Astronomer D. Phil. Lansberg. in Zealand about Astronomical matters, did most seriously affirm unto me, he should never be dissuaded from that Truth. This which he was pleased to style a truth, I should readily receive as an Hypothesis, and so be easily led on to the consideration of the imbecility of Man's apprehension, as not able rightly to conceive of this admirable opifice of God or frame of the world, without falling foul on so great an absurdity. Yet sure I am, it is a probable inducement to shake a wavering understanding. And which adds somewhat more, I understand by Galilaeus a Florentine, and a most acute and learned Mathematician, that an Italian Gentleman of the Family of the Marsilii hath lately found the mutation of the Terrestrial Meridian's, and penned a treatise thereof not yet published, which the said Galilaeus hath seen and read constupore, not without amazement. His words are these.  
Surge di present una quinta novita, dalle quale si possa arguir mobilita nel globo terrestre, mediante quello, che sottilissimament va scoprendo l' illustrissimo S. Caesare della nobilissima famiglia de i Marsilij di Bologna, pur ' Academico Lincio, il quale in una dottissima scrittura va esponendo, come ha' osservato una continua mutazione, bench tardissima, nella linea Meridiana; della quale scrittura, da me ultimament con stupore veduta, spero che dovera fare coppia a tutti gli studio si delle maraviglie della natura.  
Which in English runs thus.  
Now there ariseth a fifth novelty, from which we may argue the mobility of the tererestriall Globe, by the means of that which most subtllie the most mustruous Gentleman Sig: Caesar of the most noble family of the Marsilij of Bologna a Lyncean Academic also, hath discovered, who in a most learned tract plainly showeth how he hath observed a continual mutation, although very slow, in the Meridian line; which discourse, which with wonder I lately saw, I hope he will impart to all those who are Studious of the wonders of nature.  
Surely if it be so, the due consideration of the premises doth (as I conceive) lay open a fair way for the salving of that Irregular Motion imputed to the Axis of the Earth. I mean the alterable Obliquity of the Ecliptic, which to deny (as some yet do, not without great violence offered to the Ancients) I shall hardly (without very strong argument) be persuaded. I pretermit likewise a suppofition which might be made of the correspondent motion of the Pole of the Magnet with those of some of the Planets, and diverse other conceits, which must be all left to future times to discover, this Invention being but newly presented to the world in its infancy.  
Gresham College 5 Cal. Aug. 1634.   

Errata Typographica.  
PAg. 7 lin. 1. for Gilberts read Gilbert. Pag. 7 lin, 16 for D●●ford read Diepford. p. 9 lin 19 for the same way, read the way. p. 9 lin. 27 for 9 ½ read 9 ⅓. p, 13, lin, 12, for internal read interval: pag, 16 lin last for must read most:  
FINIS.