IMPERIAL STANDARD TROY POUND WEIGHT. 
475 
specific gravity with the metal of the new pounds compared by him with the imperial 
standard. Indeed, he has nowhere noted (or, if he had noted, has nowhere published,) 
the state of the barometer and thermometer at the time of his comparisons ; an omis- 
sion which is only allowable when both weights are supposed to be of the same spe- 
cific gravity and expansion *. 
On the other side, Captain Nehus, who had the imperial standard troy pound 
several months under his eyes, is decidedly of opinion that it was not of brass. He 
declares that its dark brown colour left no doubt that it must be of copper or bell- 
metal. Mr. Robinson, whose decision was called in aid, thought it (from the form 
of the rands, which the impression of the stamps had raised, and from the fine poro- 
sity of the surface,) to be of copper. 
21. We have thus private opinion against private opinion, and the question still 
remains undecided. Under the impression that in the Parliamentary Reports about 
the year 1758, when the imperial standard troy pound was made, something more 
decisive respecting the metal of that pound might be found, I carefully perused 
the second volume of the “ Reports from Committees of the House of Commons. Re- 
“ printed (1803) by order of the House. Miscellaneous Subjects 1738 — 1765. — Folio.” 
It contains two Reports from the Committees appointed to inquire into the original 
standards of weights and measures, both presented by Lord Carysfort : the first on 
May 26, 1758, the second on April 11, 1759. It appears that Mr. Harris, then 
Assay-Master of the Mint, presented to the first Committee three troy pounds made 
under his direction, whose weight was determined by a mean taken from the best old 
standards existing at that time, as described in the following words (p. 437 b) : viz. 
“Therefore to ascertain the troy pound, according to the aforesaid experiments,” 
(the mean taken from several standards,) “ your Committee directed three several 
“ troy pounds to be made under the direction of Mr. Harris, to be marked as 
“ follows 
[Here a rough sketch is inserted, showing the form of the imperial standard 
troy pound, and the marks stamped upon it.] 
“ and these have been accordingly made and adjusted with very curious and exact 
“ scales of his at the Mint, and found to agree with the result of the experiments 
“ made by the Committee : one of these weights is also produced herewith.” 
* Supposing Bate’s metal, from which the new pounds were made, to be 8 - 0 specific gravity, and the im- 
perial standard to be 8‘1 (being a difference of only 0‘1 in specific gravity from Bate’s pounds), this would 
have required under common atmospheric circumstances (barom. 30’0, therm. 62°) a correction of 00109 
grains to be applied to the comparisons, in order to obtain the true difference of weight. It is evident that 
Captain Katf.r, who gave his comparisons in ten thousandth parts of a grain, would not have neglected cor- 
rections which for so small a difference in the specific gravity affect the results even to hundredths of a grain, 
if he had not considered the metal of the old pound identical with that of the new pounds. But of this he 
could know nothing for certain. 
3 p 2 
