500 PHILOSOPHICAL TRANSACTIONS. [ANNO 1 7QQ. 



all bodies, and in all cases, diminish their apparent weights. To determine whether 

 this is actually the case or not, I made the following experiment. Having provided 

 2 bottles, as nearly alike as possible, and in all respects similar to those made use 

 of in the experiments above-mentioned, into one of them I put 4012.46 grains of 

 water, and into the other an equal weight of mercury; and, sealing them herme- 

 tically, and suspending them to the arms of the balance, I suffered them to acquire 

 the temperature of my room, Gl°; then, bringing them into a perfect equilibrium 

 with each other, I removed them into a room in which the air was at the tempera- 

 ture of 34°, where they remained 24 hours. But there was not the least appear- 

 ance of either of them acquiring, or losing, any weight. 



Here it is very certain, that the quantity of heat lost by the water, must have 

 been very considerably greater than that lost by the mercury; the specific quantities 

 of latent heat in water and in mercury, having been determined to be to each other 

 as 1000 to 33; but this difference in the quantities of heat lost, produced no sen- 

 sible difference on the weights of the fluids in question. Had any difference of 

 weight really existed, had it been no more than one millionth part of the weight of 

 either of the fluids, I should certainly have discovered it; and had it amounted to 

 so much as frrlWr P art of that weight, I should have been able to have measured 

 it; so sensible, and so very accurate, is the balance which I used in these 

 experiments. 



I was now much confirmed in my suspicions, that the apparent augmentation of 

 the weight of the water on its being frozen, in the experiments before related, 

 arose from some accidental cause; but I was not able to conceive what that cause 

 could possibly be, — unless it were, either a greater quantity of moisture attached to 

 the external surface of the bottle which contained the water, than to the surface of 

 that containing the spirits of wine, — or some vertical current or currents of air, 

 caused by the bottles, or one of them not being exactly of the temperature of the 

 surrounding atmosphere. Though I had foreseen, and, as I thought, guarded suf- 

 ficiently against these accidents, by making use of bottles of the same size and 

 form, and which were blown of the same kind of glass, and at the same time; 

 and by suffering the bottles, in the experiments, to remain for so considerable a 

 length of time exposed to the different degrees of heat and of cold, which alter- 

 nately they were made to acquire; yet, as I did not know the relative conducting 

 powers of ice and of spirit of wine with respect to heat; or, in other words, the 

 degrees of facility or difficulty with which they acquire the temperature of the me- 

 dium in which they are exposed; or the time taken up in that operation; and con- 

 sequently was not absolutely certain as to the equality of the temperatures of the 

 contents of the bottles at the time when their weights were compared, I determined 

 now to repeat the experiments, with such variations as should put the matter in 

 question out of all doubt. I was the more anxious to assure myself of the real 

 temperatures of the bottles and of their contents, as any difference in their tem- 

 peratures might vitiate the experiment, not only by causing unequal currents in the 



