Faraday to John William Lubbock   21 September 1835

21 Septr 1835 | Royal Institution

Dear Sir

I thought I could have called on you before this and so have acknowledged your note in person[.]

I think it is much better that Mr Russel[l]¹ should examine the results[.] Why should you take that trouble on you which another can take when there is so much that can not be so transferred²[.]

The table you speak of must I think be one of those we have but in a different form: for the argument is Specific Gravity in that I refer to & the second column expresses the proportion of proof spirit by weight in a hundred parts by weight of any stronger or weaker spirit at any given temperature. If we can replace the true Specific Gravity by the observed Specific Gravity (which I presume is not difficult) this will be the identifying table i.e it will shew the same strength for the same spirit at different temperatures.

But whilst the Excise adopt the system of measuring instead of weighing spirit this table will not do for levying the duty by because it does not give the proportion in any given bulk of spirit and because the bulk changes by temperature whilst the weight remains the same: and as the officer when he gauges or measures does not correct the whole volume to what it would be at 62° or standard temperature so the numbers which at different temperatures would come out the same for the same spirit by this table must come out differently by the table which he really does use or is to use. The correction in fact for increase or diminution of bulk being introduced into the second column of this table thus the observed S.G in this table at the temperature of 80° would indicate the number of gallons of proof spirit at 62° in 100 gallons of the examined spirit at 80° whereas the next day the observed S.G at the temperature of 40° for the same spirit would indicate the number of gallons of proof spirit at 62° in 100 gallons of the examined spirit at 40°. As 100 gallons at 80° & at 40° are different quantities by weight the indications at these two temperatures would of course not be the same[.]

Ever My dear Sir | Very Truly Yours | M. Faraday

J.W. Lubbock Esq | &c &c &c