DENSITIES OF THE TROY POUNDS CONSTRUCTED IN 1758. 
801 
known number of divisions of the tube suffered to run into a light glass jar in which 
it is weighed. This process is to be repeated till the upper end of the column of 
mercury descends to the point P. 
The stereometer was mounted in a room in Mr. Bingley’s house at the Mint, 
September 12, 1843, and a few comparisons made of the volumes of V, O, M. The 
results, however, in consequence of the unequal heating of different parts of the 
stereometer in putting it together, did not prove satisfactory. On the 16th, the 
volumes of O, M and C, a hollow cylinder of brass, were compared with better 
success. The unit of volume being the volume of a grain of water at its maximum 
density, these observations gave ?;0+5'3=t;M=vC— 0'6. 
By observations made August 19, 1843, C: 2:600001 grains of brass +78'832 
grains of platinum in air (^=24‘23, & = 756'78). C in water (^= 1 8T) :C!: — 9’707 
grains of platinum. Hence C in air (^=24‘23, h=756‘78) in water (^=18T) 
+ 600’001 grains of brass +88'539 grains of platinum in air (^=24‘23, b=756'7S). 
The weights displace 0*092 grain of air; C displaces 0*810 grain of air. Hence C 
displaces 689*258 grains of water at 18*1, and the volume of C at 0° is equal to the 
volume of 689*562 grains of water at its maximum density. Hence wO = 683*66, 
^;M = 688*96. By weighing in air and in water it was found that wV=706*34. The 
large differences between these numbers show that the volume of the lost standard 
cannot be inferred with any high degree of probability from a comparison of the 
volumes of the three remaining pounds. 
The only resource now remaining was indicated by Professor Schumacher’s 
remarks on the figure of the lost troy pound: — ‘'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- 
U. 
Fig. 6. 
sumed the two Houses of Parliament in 1834, the only thing 
remaining which can preserve an idea of it.” An applica- 
tion was made to Professor Schumacher for the original 
drawing, if still in existence, or for any information that 
would show how far the accuracy of the wood engraving 
might be depended upon. In his reply, dated October 3, 
1843, he wrote as follows: — “ The dimensions of the lost 
standard were only taken with a bow-legged compass in 
order to give an accurate drawing of the standard pound, 
and in this respect I called them in my papers accurate, but 
they certainly are not sufficient to give a near approxima- 
tion of its volume. I find that he (Captain v. Nehus) has 
immediately transferred the taken dimensions to paper. 
This paper, with the original drawing, has served to give 
the woodcut in the Philosophical Transactions, but to my best recollection Mr. Baily 
