AND MODERN PHYSICS. 41 



evening, and I have been there preparing their experiments in 

 the gaslight There is to be a meeting in my rooms to-night 

 to discuss Adam Smith's * Theory of Moral Sentiments, 1 so I 

 must clear up my litter presently. I am working away at 

 electrfcUy again, and have been working my way into the 

 views of heavy Cerman writers. It takes a long time to 

 reduce to order all the notions one gets from these men, but 

 1 hope to see my way through the subject and arrive at some- 

 thing intelligible in the way of a theory. .... 



"The colour trick came off on Monday, 7th. I had the 

 proof-sheets of my -paper, and was going to read; but 1 

 changed my mind and talked instead, which was more to the 

 puqiose. There were sundry men who thought that blue and 

 yellow make green, so I had to undeceive them. I have got 

 Hay's book of colours out of the Tniv. Library, and am 

 working through the s]>eciniens, matching them with the top. 

 I have a new trick of stretching the string horizontally above 

 the top, so as to touch the upper part of the axis. The motion 

 of the axis sets the string a-vibrating in the same time with 

 the revolutions of the top, and the colours are seen in the haze 

 produced by the vibration. Thomson has been spinning the 

 top, and he finds my diagram of colours agrees with his 

 exiierimenU, but he doubts about browns, what is their 

 composition. I have got colcothar brown, and can make white 

 with it, and blue and green ; also, by mixing red with a little 

 blue and green and a great deal of black, I can match colcothar 

 exactly. 



"I have been perfecting my instrument for looking into 

 the eye. Ware has a little beast like old Ask, which sits quite 

 steady and seems to like being looked at, and I have got 

 several men who have large pupils and do not wish to let me 

 look in. I have seen the image of the candle distinctly in all 

 the eyes I have tried, and the veins of the retina were visible 

 in some ; but the dogs' eyes showed all the ramifications of 

 veins, with glorious blue and green network, so that you might 

 copy down everything. I have shown lots of men the image 

 in my own eye by shutting off the light till the pupil dilated 

 and then lotting it on. 



