152 THE LIFE OF JAMES D. FORBES. [ cnAP - 



hopeful and the most brilliant for a person furnished as 

 you are with all the necessary weapons, one whose 

 clearness of mathematical apprehension may disem- 

 barrass them of some of the cumbrous learning and 

 merely plausible speculations by which they have been 

 overlaid, and whose love of experimental laws may enable 

 him to trace analogies which will ultimately point to the 

 identification of classes of phenomena still distinct. 



* You are, I apprehend, already well read in the undu- 

 latory theory of light, though perhaps the original memoirs 

 of Fresnel and Airy are not all known to you, and well 

 deserve being read, as the kind of investigation which they 

 point to and recommend is, I think, far more satisfactory 

 than the endless memoir of Cauchy and of some others, 

 even in this country, whom I could mention. That there 

 are real outstanding difficulties to the theory of the trans- 

 verse vibrations, none, I apprehend, who understand the 

 present state both of the experimental and mathematical 

 evidence, can deny. 



* From this subject, which you should prosecute with 

 pieces of mica and Iceland spar and Nicol's prism in your 

 hand, you should turn to heat. Fourier you have pro- 

 bably read already. I doubt whether Poisson is worth 

 the labour, even to you, who would read it comparatively 

 easily. The researches of Melloni and my own on radiant 

 heat, of which you will find an abstract in Powell's forth- 

 coming Keport, contain no doubt, as far as they are 

 correct, the elements of a just theory of heat, parallel 

 with that of light ; and here a great deal is to be done 

 and will soon be done ; and I should be much more glad 

 that you did it than that it should be imported from 

 abroad. I assure you it is with great diffidence that I 

 presume to offer anything like advice to one so competent 

 to judge for himself and with so many able advisers 

 besides. Should you think well of the suggestions I have 

 made, I will endeavour, so far as I can, to aid in carrying 

 them into effect. 



* With kind regards to Mr. and Mrs. Ellis, believe me, 

 my dear friend, most sincerely yours/ 



