AND THE THKOUY OF LIGHT. 59 



every revolution of the larger wheel the smaller makes 

 eight revolutions. On the pivot of the axle of the smaller 

 wheel there is a small chuck or holdfast^ by which the disc 

 or figure^ or the substance reflecting the light with which 

 it is intended to operate, is fixed to the machine ; this was 

 always a small piece of card of various forms. I tried 

 thin plates of silver, but they did not suit the purpose so 

 well as the bits of Bristol board. I expect, however, all 

 these experimeiits to be improved by means of more per- 

 fect apparatus, as I have hitherto not been able to devote 

 as much attention to them as I could wish, my time being 

 too much and too laboriously occupied in a most arduous 

 profession. Indeed the whole of the experiments were 

 first of all made under a jet of gaslight, after eight o'clock 

 in the evening, and it was sometimes months before I 

 could get them properly verified by sun light. The ex- 

 periments are therefore stiil in their infancy, and leave a 

 wide field open for experimenters. My object being to 

 establish a principle, 1 shall leave it to others to work it 

 out. 



89. After having got the apparatus, the first experiment 

 I made was an attempt to obtain blue, and if my anticipa- 

 tions were well founded it was thought that it was merely 

 necessary to cut a small slip of card in the form of a paral- 

 lelogram, perforate it, place it on the pivot of the small 

 wheel, and then put it in motion over some place near a 

 window reflecting little light from below. But after all was 

 ready I was almost afraid to put it in motion, lest a theory, 

 which had been to me so long the greatest source of 

 pleasure, should, on being subjected to this test, be at 

 last found to be a mere delusion — a phantasy. Even 

 when I had made the experiment and found it completely 

 successful, I could scarcely believe in its reality. I was 

 most anxious to get others to verify what I saw, and one 

 in whom I had the greatest confidence not only for appre- 



