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 ½-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 making 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 instrument   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.

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TO R. B. LITCHFIELD, Esq.

                                                                     Trin. Coll., 28th November 1855
 

I am busy with questionists pretty regularly just now, slanging them one after another for the same things. As they    have just set upon me for the evening, I must stop now and get out some optical things to show them.