in the Philosophical Magazine for January. 103 



occasioned hy reading a brief notice of some experiments of 

 mine, with respect to heat, which I thought might, perhaps, 

 bear some analogy to the case of light. It is evident, how- 

 ever, that as it would be impossible to predicate beforehand 

 that heat and light are reflected according to the same law, 

 any verification of Fresnel's law" for light obtained in this 

 way could only be an analogical one, and therefore acceptable 

 only whilst photometric methods are so very imperfect as I still 

 consider them to be, however dexterously employed. 



"It was a matter, as I say, of equal surprise and pain to 

 me to find that you should have so gratuitously misinter- 

 preted my sentiments towards you, which I deliberately de- 

 clare to you were solely those of entire friendship and re- 

 spect. The object of this letter is simply to assure you of 

 this, and if I could do it in stronger terms, I would. 



" It seems to be strange and almost incredible that one 

 whose experiments I have so often quoted with respect, whose 

 results I have made known, and whose originality in the mat- 

 ter of metallic reflection I have so often vindicated at home 

 and abroad, in private conversation and in public lectures, 

 should take a pleasure in misinterpreting my expressions. 

 I am persuaded that at some future time you will do me jus- 

 tice, and in the mean time I will rather run the risk of sus- 

 taining any prejudice which your letter may excite against 

 my experiments until they appear to speak for themselvesj 

 than enter into a public disputation about statements and 

 expressions, to the certain loss both of time and temper. I 

 mean to write to Mr. Taylor to this effect, and shall per- 

 haps communicate to him the substance of this letter. 



" I am, my dear Sir, yours very truly, 

 " James D. Forbes." 



Now, Sir, after this statement it is not my intention to enter 

 into any defence of the " memorandum" inserted in your Jour- 

 nal for December (L. & E. Phil. Mag. vol. xv. p. 479.). I shall 

 correct neither Mr. Potter's statements nor his inferences, which 

 so far as they relate to myself are certainly unfounded. Had 

 I been at all aware of the extreme importance which Mr. Pot- 

 ter attributes to the particular experiments on photometry to 

 which I alluded, I should certainly have done so with far greater 

 caution. 1 imagined that Mr. Potter probably considered (as 

 I think I would have done under the circumstances) his earlier 

 contributions to physical science as subject to the revision of 

 his own maturer skill and judgement, and, until they had 

 received that revision, as open to some doubt; the subject 

 being one of such difficulty, that if Mr. Potter failed, he failed 



