purpose of finding the density of gunpowder (Ann. de Chimie, 1 797, 

 t. xxiii. p. 1), but with some improvements which I had described 

 in the Philosophical Magazine for July and December, 1834, vol. v. 

 p. 203. Let v prefixed to the symbol of any weight denote the 

 volume of that weight at Cent., the unit of volume being the 

 volume of a grain of water at its maximum density. Then, by 

 means of the Stereometer, it was found that v\ t>O=22'68, 

 0V M= 17-38. These differences show that the volume of lost 

 standard cannot be inferred with any high degree of probability from 

 a comparison of the remaining pounds. The only resource now 

 remaining was indicated by Professor Schumacher's remarks on the 

 figure of the lost standard : " As soon as the Imperial standard 

 troy pound was brought to Somerset House, Captain Nehus's first 

 care was to make an accurate drawing of its shape and marks, 

 measuring all its dimensions with the greatest care. The annexed 

 drawing represents this pound in its actual dimensions ; and is now, 

 since the original has been destroyed by the calamitous fire that con- 

 sumed the two Houses of Parliament in 1834, the only thing remain- 

 ing which can preserve an idea of it." By a comparison of the figure 

 of U in the Philosophical Transactions for 1836, with a profile of V 

 traced mechanically, the axis and the extreme diameter of the knob 

 and cylindrical portion of U, appeared to be a very little greater than 

 the corresponding dimensions of V. On comparing the profiles of 

 U and V, it did not seem possible to suppose that the volume of U 

 was less than that of V. But the volume of O, as well as that of M, 

 being less than that of V, it appeared that of the three weights V, 

 O, M, V approximated most nearly to U in volume. As the exist- 

 ing data were utterly insufficient to determine how much, if at all, 

 U exceeded V in volume, it appeared safest to assume the volumes of 

 U and V to have been equal. This course was also recommended 

 by Professor Schumacher. 



It was afterwards found that O was 0'144 grain lighter than U, 

 AO=8'4004 ; and that M was 0'047 grain lighter than U, 

 AM=8-3491. 



In a letter from William Miller, Esq., of the Bank of England, 

 dated August 22, 1855, I was apprised of the existence of a fourth 

 troy pound of 1 758. This weight was 0*249 grain heavier than U ; 

 its density =8'3175. 



