Sidebilder
PDF
ePub

of the instrument. He therefore considered this small telescope as “an epitome” of what may be done by reflections; and he did not doubt that, in time, a six feet reflector might be made which would perform as much as any sixty or hundred feet refractor. In consequence of interruptions, Sir Isaac did not proceed any farther in the construction of reflectors till the autumn of 1671.

It was during this period of his history, on the 18th of May 1669, that Sir Isaac wrote the celebrated letter of advice to his young friend, Mr. Aston, who, at the age of twenty-seven, was about to make a tour on the Continent. This “ letter" is a very interesting production.1 It does not evince much acquaintance with the ways of the world, but it shows some knowledge of the human heart, and throws a strong light on the character and opinions of its author. In his chemical studies, which, as we have just seen, he had recently commenced, his mind was impressed with some belief in the doctrines of alchemy, and he certainly pursued his experiments to a late period of his life, with the hope of effecting some valuable transmutations. Among the subjects, therefore, to which he requests Mr. Aston to pay attention, there are several which indicate this tendency of his mind. He desires him to observe the products of nature, especially in mines, with the circumstances of mining, and of extracting metals or minerals out of their ores, and refining them; and, what he considered as far more important than this, he wishes bim to observe if there were any transmutations out of one species into another, as, for example, out of iron into copper,

, out of one salt into another, or into an insipid body, &c. Such transmutations, he adds, are above all others worth his noting, being the most luciferous, and many times lucri

See APPENDIX, No. I.

ferous experiments too, in philosophy! Among the particular observations to which he calls the attention of his friend, is that of a certain vitriol, which changes iron into copper, and which is said to be kept a secret for the lucrative purpose of effecting that transmutation. He is to inquire also whether in Hungary, or in the mountains of Bohemia, there are rivers whose waters are impregnated with gold, dissolved by some corrosive fluids like aqua regis; and whether the practice of laying mercury in the rivers till it be tinged with gold, and then separating the gold by straining the mercury through leather, be still a secret or openly practised. There was at this time in Holland a notorious alchemist of the name of Bory, who, as Sir Isaac says, was some years since imprisoned by the Pope, in order to extort from him secrets of great worth, both “as to medicine and profit," and who made his escape into Holland, where they granted him a guard.

" I think,” adds Sir Isaac, “ he usually goes clothed in green : Pray, inquire what you can of him, and whether his ingenuity be any profit to the Dutch !” We have not been able to discover the results of Mr. Aston's inquiries, but whatever they were they did not damp the ardour of Newton in his chemical researches, nor extinguish the hope which he seems to have cherished, of making " philosophy lucriferous,” by transmuting the baser metals into gold.

But however fascinating these studies were to our young philosopher, he did not permit them to interfere with his nobler pursuits. At the very time when writing to Mr. Aston, we find him occupied with his fluxionary calculus, and transmitting to Dr. Barrow his celebrated paper On Analysis by Equations with an infinite number of terms, with permission to communicate it to their mutual friend, Mr. Collins. In announcing this communication on the 20th June 1669, and promising to send it by the next opportunity, Dr. Barrow keeps the name of its author a secret, and merely tells Mr. Collins that he is a friend staying at Cambridge, who has a powerful genius for such matters. In his next letter of the 31st July, accompanying the paper, he expresses the hope that it will not a little delight him ; and, in a third letter to Collins of the 20th August, he mentions how much he is pleased with the favourable opinion which his correspondent has of it, and adds, that “the name of the author is Newton, a Fellow of our College, and a young man, who is only in his second year since he took the degree of Master of Arts, and who, with an unparalleled genius, has made very great progress in this branch of mathematics."

CHAPTER III.

NEWTON SUCCEEDS BARROW IN THE LUCASIAN CHAIR-HYPERBOLIC LENSES

PROPOSED BY DESCARTES AND OTHERS-OPINIONS OF DESCARTES AND

ISAAC VOSSIUS ON COLOURS--NEWTON DISCOVERS THE COMPOSITION OF

WHITE LIGHT, AND THE DIFFERENT REFRANGIBILITY OF THE RAYS THAT

COMPOSE IT-HAVING DISCOVERED THE CAUSE OF THE IMPERFECTION

OF REFRACTING TELESCOPES, HE ATTEMPTS THE CONSTRUCTION OF

REFLECTING ONES-CONSTRUCTS A SECOND REFLECTING TELESCOPE IN

1668, WHICII IS EXAMINED BY THE ROYAL SOCIETY, AND SHEWN TO

THE KING-DISCUSSIONS RESPECTING THE GREGORIAN, NEWTONIAN, AND

CASSEGRAINIAN TELESCOPE-JAMES GREGORY THE INVENTOR OF THE RE

FLECTING TELESCOPE-ATTEMPTS TO CONSTRUCT ONE-NEWTON MAKES

A SPECULUM OF SILVERED GLASS-GLASS SPECULA BY SHORT IN 1730, AND AIRY IN 1822-HADLEY CONSTRUCTS TWO FINE REFLECTING TELE

TELESCOPES BY BRADLEY, MOLYNEUX, AND HAWKSBEE-SHORT'S REFLECTING TELESCOPES WITH METALLIC SPECULA-MAGNIFI

SCOPES

CENT TELESCOPE OF SIR WM, HERSCHEL WITH A FOUR FEET SPECULUM

MUNIFICENCE OF GEORGE III.-ASTRONOMICAL DISCOVERIES OF SIR

WM, HERSCHEL-TELESCOPES OF SIR J. HERSCHEL AND MR. RAMAGE

-GIGANTIC TELESCOPE OF THE EARL OF ROSSE WITH A SIX FEET SPE

CULUM-PROGRESS OF TELESCOPIC DISCOVERY-PROPOSAL TO SEND A

FINE TELESCOPE TO A SOUTHERN CLIMATE,

IN 1669, when Dr. Barrow had resolved to devote himself to the studies and duties of his profession, he resigned the Lucasian Professorship of Mathematics, in favour of Newton. His appointment took place on the 29th October, and we may now consider him as having entered on that brilliant career of discovery, the history of which will form the subject of some of the following chapters. It had been long known to every writer on optics, and to every practical optician, that lenses with spherical surfaces, such as those now in common use, did not give distinct images of objects. This indistinctness was believed to arise solely from their spherical figure, in consequence of which the rays which passed through the marginal or outer parts of the lens were refracted to a focus nearer the lens than those which passed through its central parts. The distance between these foci was called the spherical aberration of the lens, and various methods were suggested for diminishing or removing this source of imperfection. Descartes? had shewn that hyperbolic lenses refracted the rays of light to a single focus, and we accordingly find the carly volumes of the Philosophical Transactions filled with schemes for grinding and polishing lenses of this form. Newton had made the same attempt, but finding that a change of form produced a very little change in the indistinctness of the image, he thought that the defect of lenses, and the consequent imperfection of telescopes, might arise from some other cause than the imperfect convergency of the incident rays to a single point. This happy conjecture was speedily confirmed by the brilliant discovery of the different refrangibility of the rays of light,-a discovery which has had the most extensive applications to every branch of science, and (what is very rare in the history of inventions) one to which no other person has made the slightest claim.

No plausible conjecture, even, had been formed by the predecessors of Newton respecting the nature and origin of colours. Descartes believed them to be a modification of light depending on the direct or rotatory motion of its particles. Grimaldi, Dechales, and others regarded them as arising from different degrees of rarefraction and condensation of light. Gregory defines colour to be the hue

| Dioptrice, cap. vii. ix., 1629.

« ForrigeFortsett »