498 PHILOSOPHICAL TRANSACTIONS. [ANNO 17 QQ. 



its fluid state; but some irregularity in the manner in which the water lost the 

 additional weight which it had appeared to acquire on being frozen, when it was 

 afterwards thawed, as also a sensible difference in the quantities of weight appa- 

 rently acquired in the different experiments, led me to suspect, that the experiment 

 could not be depended on for deciding the fact in question ; I therefore repeated it, 

 with some variations and improvements; but, before I give an account of my fur- 

 ther investigations relative to this subject, it may not be amiss to mention the me- 

 thod I pursued for discovering whether the appearances mentioned in the foregoing 

 experiments might not arise from the imperfections of my balance; and it may 

 likewise be proper to give an account, in this place, of an intermediate experiment 

 which I made, with a view to discover, by a shorter route, and in a manner less 

 exceptionable than that above-mentioned, whether bodies actually lose, or acquire, 

 any weight, on acquiring an additional quantity of latent heat. 



My suspicions respecting the accuracy of the balance arose from a knowledge, 

 which I acquired from the maker of it, of the manner in which it was constructed. 

 The 3 principal points of the balance having been determined, as nearly as possible, 

 by measurement, the axes of motion were firmly fixed in their places, in a right 

 line, and the beam being afterwards finished, and its 2 arms brought to be in equi- 

 librio, the balance was proved by suspending weights, which before were known to 

 be exactly equal, to the ends of its arms. If with these weights the balance re- 

 mained in equilibrio, it was considered as a proof that the beam was just; but if 

 one arm was found to preponderate, the other was gradually lengthened, by beating 

 it on an anvil, till the difference of the lengths of the arms was reduced to nothing, 

 or till equal weights, suspended to the 2 arms, remained in equilibrio; care being 

 taken before each trial to bring the 2 ends of the beam to be in equilibrio, by 

 reducing, with the file, the arm which had been lengthened. 



Though, in this method of constructing balances, the most perfect equality in 

 the lengths of the arms may be obtained, and consequently the greatest possible 

 accuracy, when used at a time when the temperature of the air is the same as when 

 the balance was made, yet as it may happen, that in order to bring the arms of the 

 balance to be of the same length, one of them may be much more hammered than 

 the other, I suspected it might be possible that the texture of the metal forming the 

 2 arms might be rendered so far different, by this operation, as to occasion a differ- 

 ence in their expansions with heat; and that this difference might occasion a sen- 

 sible error in the balance when, being charged with a great weight, it should be 

 exposed to a considerable change of temperature. 



To determine whether the apparent augmentation of weight, in the experiments 

 above related, arose in any degree from this cause, I had only to repeat the experi- 

 ment, causing the 2 bottles a and b to change places on the arms of the balance; 

 but as I had already found a sensible difference in the results of different repetitions 

 of the same experiment, made as nearly as possible under the same circumstances, 

 and as it was above all things of importance to ascertain the accuracy of my balance, 



