31 
new standards of weights and measures. 
weights and a circular piece of plate glass ( the use of which 
will be presently described), and the whole was counter- 
poised. 
The division at which the index of the balance stood was 
noted, and the gallon weight removed ; the gallon was then 
nearly filled with distilled water by means of a small glass 
syphon, so contrived by Mr. Bate as to prevent the intro- 
duction of bubbles of air. The temperature of the water was 
then taken as well as the height of the barometer, and the 
filling of the gallon continued until the water rose percepti- 
bly a little above its mouth. The piece of plate glass before- 
mentioned, and which had a small hole drilled in its centre, 
was then carefully placed upon the top of the gallon, when 
the superabundant water passed through the hole to the upper 
surface of the glass, and was removed by drawing it with the 
mouth into a capillary glass tube. 
The difference of the expansion of water, and of brass, 
being an object of the highest importance in the present 
operations, I was glad to find that Mr. Bate had made nume- 
rous experiments upon this subject, and I had had sufficient 
experience of his care to place great reliance upon his con- 
clusions. It will be seen that the considerable range of tem- 
perature under which the experiments with the gallons 
No. 1, 3, and 4 , were made, and the uniformity of the results 
fully justify this confidence, and form very conclusive evi- 
dence of the accuracy of the corrections employed. 
But besides the correction for the difference of the expan- 
sion of water and of the brass vessel, another allowance is 
necessary for the buoyancy of the atmosphere in cases where 
extreme accuracy is required. The gallon is to contain ten 
