the Weight ascribed to Heat. 185 
that means its apparent weight might be increased ; and having 
found by a former experiment, of which I have already had the 
honour of communicating an account to the Royal Society, that 
the gilt surfaces of metals do not attract moisture ; instead of 
the glass globes filled with mercury, I made use of two equal 
solid globes of brass, well gilt and burnished, which I sus- 
pended to the arms of the balance, by fine gold wires. 
These globes, which weighed 4975 grains each, being wiped 
perfectly clean, and having acquired the temperature (6i°) of 
my room, in which they were exposed more than twenty-four 
hours, were brought into the most scrupulous equilibrium, and 
were then removed, attached to the arms of the balance, into 
a room in which the air was at the temperature of 2 6°, where 
they were left all night. 
The result of this trial furnished the most satisfactory proof 
of the accuracy of the balance; for, upon entering the room, I 
found the equilibrium as perfect as at the beginning of the ex- 
periment. 
Having thus removed my doubts respecting the accuracy of 
my balance, I now resumed my investigations relative to the 
augmentation of weight which fluids have been said to acquire 
upon being congealed. 
In the experiments which I had made, I had, as I then imagined, 
guarded as much as possible against every source of error and 
deception. The bottles being of the same size, neither any occa- 
sional alteration in the pressure of the atmosphere during the 
experiment, nor the necessary and unavoidable difference in the 
densities of the air in the hot and in the cold rooms in which they 
were weighed, could affect their apparent weights; and their 
shapes and their quantities of surface being the same, and as they 
