LVIII 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
liamentary standards of length and weight destined to replace those 
destroyed in 1834. A number of weights had been very accurately 
compared with the lost standard; namely, in 1824 or 1825, by 
Capt. Kater, five troy pounds of gun-metal, destined respectively 
for the use of the Exchequer, the Royal Mint, and the cities of 
London, Edinburgh, and Dublin ; and in 1829, by Capt. v. Nehus, 
two troy pounds of brass and one of platinum, all in the custody 
of Prof. Schumacher, and a platinum troy pound belonging to the 
Royal Society. The first step for recovering the mass of the lost 
standard was manifestly to compare these weights among themselves,, 
and upon so doing it was found that for the brass and gun-metal 
weights the discrepancies between the weighings made in 1824 and 
1844 amounted to 0*0226^ of a grain, while for the two platinum 
weights the discrepancies between the weighings made in 1829 and 
1845 was only 0’00019^ of a grain. With a single exception, all 
the new brass or gun-metal weights had become heavier since their 
first comparison with the lost standard, the change being probably 
due to oxydation of their surfaces, and on that account the new 
standard was made to depend solely upon the two platinum weights. 
For convenience of reference these weights were designated respec¬ 
tively Sp (Schumacher’s platinum), and RS (Royal Society). A 
provisional platinum troy pound, T, intermediate in mass between 
Sp and RS was next prepared, and from 286 comparisons made in 
January, February, July, and August, 1845, it was found that in a. 
vacuum^ 
T = Sp + 0’00105 grain, 
while from 122 comparisons made in January, July, and August,. 
1845, 
T = RS — 0’00429 grain. 
By combining these values with the results of the weighings- 
made in 1824-29, namely, 
Sp = U — 0’52956 grain, 
RS = U - 0-52441 grain, 
where U designates the lost standard—the comparisons with Sp 
gave 
T = U - 0-52851 grain, 
while those with RS gave 
T = U - 0-52870 grain. 
140, p. 772. 
2 40, p. 941. 
40, pp. 819-20. 
