OF NEWTON'S OPTICS. 



states, that he cannot concede to him 

 greater merit than that of having had a 

 glimmering of the true explanation of 

 the interior bow. From the manner in 

 which he explains the course of the rays, 

 it seems doubtful whether he was even 

 aware of the second refraction which the 

 rays suffered on their emergence from 

 the drop. Montucla, however, denies 

 him any participation in the discovery of 

 the cause of the exterior bow, and states 

 that he had not the most remote idea of 

 the double reflection which constitutes 

 the character of this phenomenon. Dr. 

 Brewster, on the other hand, an high 

 authority on this subject, says, that 

 although his attempt at explaining the 

 interior bow is sufficiently absurd, yet 

 that it is impossible for any philosopher, 

 free from the influence of national par- 

 tiality, to deny that the Italian prelate 

 has given such an explanation of the 

 general phenomena of the exterior bow, 

 that any other philosopher of more 

 optical knowledge, and of inferior acute- 

 ness, could not fail, without any stretch 

 of intellect, to give precision and perfec- 

 tion to the explanation. Newton's own 

 opinion appears to have been similar to 

 that last quoted. 



About the period at which De Dominis 

 instituted his experiments, Kepler pro- 

 posed an explanation of the rainbow, in 

 a letter to Harriot. He conceives that 

 the solar ray which touches a drop of 

 rain is refracted, and penetrating the 

 drop meets the posterior surface, from 

 which it undergoes a partial reflection ; 

 that again penetrating the drop, it 

 emerges, and at its emergence undergoes 

 a second refraction, after which it reaches 

 the eye of the spectator. Kepler here 

 approximated very closely to the true 

 solution of the problem. If, however, 

 the ray which finally reached the eye 

 were a tangent to the drop when inci- 

 dent on it, the bow would be much 

 smaller than it is known to be. Har- 

 riot did not, on this occasion, give to the 

 subject that attention to which its im- 

 portance entitled it, but excused himself 

 to Kepler by business and indisposition, 

 promising that he would one day develop 

 the mystery. It is evident that he agreed 

 with Kepler in the necessity of a reflection 

 intermediate between the two refrac- 

 tions, which, indeed, considering the re- 

 lative positions of the sun, the drops, 

 and the spectator, was sufficiently ob- 

 vious. But he said nothing which can 

 guide us to a knowledge of how far he 

 was acquainted with the true theory of 

 the phenomenon. 



(8.) The accumulated facts and experi- 

 ments furnished by various philosophers, 

 and the numerous suggestions of optical 

 writers, on the use and applications of 

 lenses, and their combinations, among 

 which those of Roger Bacon and Bap- 

 tista Porta are more especially entitled 

 to notice, had now prepared the way for 

 the construction, we will not say inven- 

 tion, of telescopes and microscopes. The 

 approach to the construction of the 

 telescope, like the passage from dark- 

 ness through twilight to broad day, is so 

 gradual, that it is almost impossible, if 

 we deny the invention to Bacon, to as- 

 sign it to any other. Descartes assigns 

 the discovery to James Metius, a Dutch- 

 man, and a citizen of Alkmaer. He 

 commences his Dioptrics with this hu- 

 miliating confession : " To the shame 

 of science, this admirable invention was 

 the fortuitous result of experience. About 

 thirty years ago, a person named James 

 Metius, who had never studied, although 

 his father and brother had devoted them- 

 selves to the profession of mathematics, 

 but who took great pleasure in making 

 mirrors and burning glasses, having 

 occasion for glasses of different forms, 

 happened to look through two of them, 

 of which one was convex and the other 

 concave. He applied them to the ends 

 of a tube, and thus happily formed the 

 first telescope." 



Not satisfied with this origin of the 

 telescope, some authors have sought for 

 one still more humiliating to science, 

 and to the pride of human intellect. It 

 is said that the children of a spectacle- 

 maker at Middleburg, happening to play 

 in their father's shop, were amusing 

 themselves with looking at a weather- 

 cock with two glasses, the one convex 

 and the other concave ; and happening 

 to place them in a fit position, they be- 

 held the object magnified, and brought 

 close to them. They communicated their 

 astonishment to their father, who, to 

 make the experiment more convenient, 

 fixed the glasses in a proper manner up- 

 on a board. Presently another person ad- 

 justed the lenses at the ends of a tube, so 

 as to exclude the lateral light, which dis- 

 turbed the vision, and thus made the ob- 

 jects appear more brilliant and distinct. 

 The next improvement, which trod upon 

 the heels of the last, was to use tubes 

 which moved one within another, so as 

 to admit of any adjustment of the lenses 

 which might be found necessary. 



Without insisting further on this ac- 

 count of the invention, which, besides 

 being unsupported by evidence, is at- 



