CHAP. VII.] BACHELOR-SCHOLAR. 215 



way, I did not get the teetotum you were to leave for 



me. 



P.S. I hope you have got the proof of the plate as 

 well as of the paper. If not, write to Messrs. Johnston, 

 engravers, 4 St. Andrew Square, Edinburgh. 



To R B. LITCHFIELD, Esq. 



Trin. Coll, 6th June 1855. 



It is hard work grinding out "appropriate ideas," as 

 Whewell calls them. However, I think they are coming 

 out at last, and by dint of knocking them against all the 

 facts and ^--digested theories afloat, I hope to bring them to 

 shape, after which I hope to understand something more 

 about inductive philosophy than I do at present. 



I have a project of sifting the theory of light and mak- 

 ing everything stand upon definite experiments and definite 

 assumptions, so that things may not be supposed to be 

 assumptions when they are either definitions or experiments. 



I have been looking into all the dogs' eyes here to see 

 the bright coating at the back of the eye, thro' an instru- 

 ment I made to that end. The spectacle is very fine. I 

 remember the appearance of Mungo's eyes at Cheltenham. 

 He would be the dog to sit. Human eyes are very dark 

 and brown as to their retina, but you can see the image of 

 a candle quite well on it, and sometimes the blood-vessels, 

 etc. 



FROM WILLIAM DYCE CAY, Esq., TO JOHN C. M. 



(Glasgow, at the Meeting of the British Association). 



18th September 1855. 



Sir David Brewster was upon the triple spectrum. As 

 far as I can understand, he believes the spectrum to be 

 composed of three colours red, blue, and yellow; and that 

 the intermediate colours are composed of mixtures of these, 

 as, for example, the green from a mixture of blue and 

 yellow, which, I think, is different from what James be- 



