afcribed to Heat. 3P5 



them afterward into the cold, and to have feen if they ftill remained in eqiiilibrio, under 

 Cucli difference of temperature; but, confidering the obftinacy with which moiftur^ 

 adheres to the furface ot glaCs, and being afraid that, fomeliow or other, notwitliftand- 

 ine aJl my precautions, one ot the globes might acquire or retain more of it than the 

 othei , and that by that means its apparent weight might be increafed ; 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 furfaces of metals do not attraft moiflure; 

 inftead of the glafs globes filled with mercury, I made ufe of two equal folid globes of 

 brafs, well gilt and burniflied, which I fufpended to the arms of the balance, by fine 

 gold wires. 



Thefe globes, which weighed 4975 grains each, being wiped perfeftly clean, and 

 having acquired the temperature of (61°) of my room, in which they were expofed 

 more than twenty-four hours, were brought into the moft fcrupulous equilibrium, and 

 were then removed, attached-to the arms of the balance, into a room in which the air 

 was at the temperature of 26°, where they were left all night. 



The refult of this trial fumilhed the moft fatisfaftory proof of the accuracy of the 

 balance ; for, upon entering the room, I found the equilibrium as perfeft as at the be- 

 ginning of the experiment. 



Having thus removed my doubts refpefting the accuracy of my balance, I now. re- 

 fumed my inveftigations relative to the augmentation of weight which fluids have been 

 faid to acquire upon being congealed. 



In the experiments which I had made, I had, as I then imagined, guarded as much 

 as poflible againft every fource of error and deception. The bottles being of the fame 

 fize, neither any occafional alteration in the preffure of the atmofphere during the ex- 

 periment, nor the necefTary and unavoidable difference in the denfities of the air in the 

 hot and in the cold rooms in which they were weighed, could affeft their apparent 

 weights ; and their fhapes and their quantities of furface being the fame, and as they 

 remained for fuch a confiderable length of time in the heat and cold to which they 

 were expofed, I flattered myfelf that the quantities of moifture remaining attached to 

 their furfaces, could not be different as fenfibly to effeft the refults of the experiments. 

 — But, in regard to this laft circumllance, I afterwards found reafonto conclude that my 

 opinion was erroneous. 



Admitting the faff ftated by Dr. Fordyce, — (and which my experiments had hi- 

 therto rather tended to corroborate than to contradift,) — I could not conceive any other 

 caufe for the augmentation of the apparent weight of water, upon its being frozen 

 than the lofs of fo great a proportion of its latent heat as that fluid is known to evolve 

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



of 



