DENSITIES OF THE TROY POUNDS CONSTRUCTED IN 1758. 
799 
gr. gr. gr. 
V displaces 0‘8616. and T— O’SIO displaces 0'33 17 of air (^=16'13, &=761-27). 
Hence V=T+0'2194 grain. 
gr. gr. gr. 
V displaces 0*8468, and T— 0*310 displaces 0*3261 of air (#=18*7, ^=755*64). 
Hence, in air (#=18*7, &=755*64), 0*3013 gr. But TiO: U — 0*0074 gr. 
Therefore V^^U— 0*3087 grain in air (#=18*7, ^=7^5*64). 
Mr. Bingley had in his possession two troy pounds of the same date. One of 
these (O) is said to be the original weight from which the standard was made for the 
House of Commons in 1758. It is distinguished by a small dot under the T, and 
the imperfection in the type of the 5 is remedied by a cut with a chisel as in V. 
This weight has since (in 1851) been purchased by the Committee. The other (M), 
in which the 5 is left imperfect, and which has the mark @ © impressed on its under 
surface, has since been presented to the Mint by its former possessor. 
O. Fig. 2. M. Fig.. 3. 
Mr. Bingley was unwilling to permit either of these troy pounds to be weighed in 
water ; Messrs. Troughton and Simms were therefore commissioned to construct an 
instrument on the principle of the Stereometer invented by M. Say for the purpose 
of determining the specific gravity of gunpowder*, but with some improvements 
which I had described in the Philosophical Magazine for July to December, 1834, 
vol. V. p. 203. It consists of two glass tubes, PQ, DB (fig. 4), of equal diameter, 
cemented into cylindrical cavities communicating with each other at their lower 
ends, in an oblong piece of iron G. In the axes of the two cavities are holes con- 
centric with the tubes. The hole under PQ is closed by a screw K, into the other is 
screwed an iron stopcock L. The upper end of the tubePQ is cemented into an iron 
cylinder N carrying a ring which surrounds the upper end of the tube DB. The 
inside of the cylinder is tapped to receive the screw of the stopcock, and the outside 
tapped so as to screw into the under end of a cup F, having its rim ground plane, 
* Annales de Chimie, 1797, tome xxiii. p. 1. 
