474 
PROFESSOR SCHUMACHER ON THE LATE 
20. It would appear, from an inspection of these results, that the true weight of the 
now destroyed imperial standard troy pound might, even after its loss, be very well 
ascertained. There are five several pounds which were compared with it only six 
years ago with extraordinary care ; these five pounds are still extant and in good 
preservation; the number of the comparisons exceeds 600, and these comparisons are 
made with excellent balances, and by a skilful and careful observer, who devoted, 
during several months, his whole time and attention to them. There remains, there- 
fore, only (since each body weighed in air loses as much of its weight as the volume 
of air weighs, which is displaced by the body,) to add on both sides of the above 
5 equations the weights of these displaced volumes of air : on one side the weight of 
the volume of air displaced by the copy, on the other side the weight of the volume 
of air displaced by the imperial standard troy pound ; or to reduce (as it is generally 
called) these weighings to a vacuum. Indeed, if it had been possible to weigh the 
bodies in a vacuum, their weights would have sustained no losses, because there was 
nothing which they could displace, and the difference of weight indicated by the 
balance would have been their true difference of weight. This true difference of 
weight is evidently likewise obtained, when, by addition of the before-mentioned 
weights of the displaced volumes of air, the weighings made in air are corrected for 
the losses which the weights of the bodies necessarily suffered from the bodies being 
obliged to put aside the medium in which they were weighed : so that both modes 
of proceeding lead to the same result, viz. to the true difference of weight of the 
bodies. 
Unhappily one of the most essential elements to calculate the volume of the now 
lost imperial standard troy pound, and of course to calculate the weight of an 
equal volume of air displaced by it, is still unknown ; I mean the specific gravity of 
that pound. Even the metal of which it was made is uncertain. It is declared to be 
a brass pound by the Act of Parliament 5 George IV. chap, lxxiv. §. 4, as follows : 
“And be it further enacted, That from and after the first day of May 1825, the 
“ standard brass weight of one pound troy weight, made in the year 1758, now in the 
“ custody of the Clerk of the House of Commons, shall be, and the same is hereby 
“ declared to be, the original and genuine standard measure of weight : and that 
“ such brass weight shall be, and the same is hereby declared to be, the unit or only 
“ standard measure of weight, from which all other weights shall be derived, com- 
“ puted and ascertained.” 
But as a law never pretends, nor can pretend, to decide upon the physical qualities 
of bodies, the expression brass weight must be understood as suggested to the legisla- 
tors by those to whom the adjusting of the weights was committed, and states of 
course only their private opinion about the metal of which the pound was made ; or, 
as this department fell under Captain Kater’s care, we may consider the words brass 
pound, brass weight, as the expression of his private opinion. This is the more likely, 
because he seems to have considered it not only as brass, but as brass of the same 
