VOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 499 



I preferred making a particular experiment for that purpose. My first idea was, to 

 suspend to the arms of the balance, by very fine wires, 2 equal globes of glass, 

 filled with mercury, and, suffering them to remain in my room till they should 

 have acquired the known temperature of the air in it, to have removed them after- 

 ward into the cold, and to have seen if they still remained in equilibrio, under such 

 difference of temperature; but, considering the obstinacy with which moisture ad- 

 heres to the surface of glass, and being afraid that, somehow or other, notwith- 

 standing all my precautions, one of the globes might acquire or retain more of it 

 than the other, and that by 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 r. s., that the gilt surfaces of metals do not at- 

 tract moisture; instead of the glass globes filled with mercury, I made use of 2 

 equal solid globes of brass, well gilt and burnished, which I suspended 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 (6l°) Of my room, in which they were exposed 

 more than '24 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(3°, where they were left all night. The result of this 

 trial furnished the most satisfactory proof of the accuracy of the balance; for, on 

 entering the room, I found the equilibrium as perfect as at the beginning of the 

 experiment. Having thus removed my doubts respecting the accuracy of my ba- 

 lance, I now resumed my investigations relative to the augmentation of weight 

 which fluids have been said to acquire on 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 occasional alteration in the pressure of the atmosphere 

 during the experiment, nor the necessary and unavoidable difference in the den- 

 sities 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 remained for such a considerable length of time in the heat 

 and cold to which they were exposed, I flattered myself that the quantities of mois- 

 ture remaining attached to their surfaces, could not be so different as sensibly to 

 affect the results of the experiments. But, in regard to this last circumstance, I 

 afterwards found reason to conclude that my opinion was erroneous. 



Admitting the fact stated by Dr. Fordyce, and which my experiments had hitherto 

 rather tended to corroborate than to contradict, I could not conceive any other 

 cause for the augmentation of the apparent weight of water, on its being frozen, 

 than the loss of so great a proportion of its latent heat as that fluid is known to 

 evolve when it congeals ; and I concluded, that if the loss of latent heat added to 

 the weight of one body, it must of necessity produce the same effect on another, 

 and consequently, that the augmentation of the quantity of latent heat must, in 



3 s 2 



