68 DISSERTATION SECOND. [part ii. 



SECTION III. 



OPTICS. 



The invention of the telescope and the microscope, the 

 discoveries made concerning the properties of light and the 

 laws of vision, added to the facility of applying mathematical 

 reasoning as an instrument of investigation, had long given 

 a peculiar interest to optical researches. The experiments 

 and inquiries of Newton on that subject began in 1666, and 

 soon made a vast addition both to the extent and importance 

 of the science. He was at that time little more than twenty- 

 three years old ; he had already made some of the greatest and 

 most original discoveries in the pure mathematics ; and the 

 same young man, whom we have been admiring as the most 

 profound and inventive of geometers, is to appear, almost at 

 the same moment, as the most patient, faithful, and sagacious 

 interpreter of nature. These characters, though certainly 

 not opposed to one another, are not often combined ; but to 

 be combined in so high a degree, and in such early life, was 

 hitherto without example. 



In hopes of improving the telescope, by giving to the glas- 

 ses a figure different from the spherical, he had begun to 

 make experiments, and had procured a glass prism, in order, 

 as he tells us, to try with it the celebrated phenomena of 

 colours* These trials led to the discovery of the different 



' Phil. Trans. Vol. VI. (1672), p. 3075. Also Hutton's 

 Abridgment, Vol. I. p. 678. The account of the experiments is 

 in a letter to Oldenburgh, date February 1672 ; it is the first of 

 Newton's works that was published. It is plain from what is 

 said above, that the phenomena of the prismatic spectrum were 

 not unknown at that time, however little they were understood, 

 and however imperfectly observed. 



