160 HERSCHEL AND HIS WORK 



by paving the way for photography, and paid back its 

 debt to astronomy by shortening the processes of its 

 art, and faithfully recording the face of the heavens, 

 as the most skilful draughtsman could not do. Truly, 

 Herschel was a seer, whose imagination captured 

 truth, though men less gifted mocked him as a dreamer. 

 The equerry in Windsor Castle was justified in assur- 

 ing Miss Burney that time would do justice to Herschel, 

 as it had done to Newton. 



Herschel's mistakes, in his subsequent inquiries, arose 

 largely from his belief in Newton's theory that light- 

 giving bodies, like the sun, emit infinitely small 

 particles, which enter the eye and affect the retina so 

 as to produce vision. Hence he spoke of the momenta 

 of these particles. His contemporary, Dr. Thomas 

 Young, maintained that light, like air, was produced 

 by waves propagated at a vast rate of speed, and in 

 immensely short lengths, through a universally diffused 

 and infinitely rare medium, called ether. l A French- 

 man, Fresnel, has got most of the credit of establishing 

 this theory. But the third question asked and 

 answered by Herschel in these papers about the 

 sun was, Is light the same or different from heat? 

 His experiments were carefully arranged and as 

 carefully made, and the conclusion reached was that 

 they are different. He also wrote two long papers on 

 the coloured rings produced when two watch-glasses, 

 or one and a plane glass, are pressed together so as to 

 leave a thin plate of air between them. Amid un- 



1 Dr. Young, "The Bakerian Lecture, Phil. Trans, for 1802, pp. 

 14, 15, "A luniniferous ether pervades the universe, rare and elastic in 

 a high degree." He was well abused by an Edinburgh Reviewer for 

 this Lecture. 



