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. 
“ Jt 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 themselves, 
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. 4*79.). 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. I 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 owm 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 
