3R4 ^" Ii'<JU7ry concerning the Weight 



which I made, with a view to difcover, by a fliorter route, and in a manner lefs ex- 

 ceptionable than that above mentioned, whether bodies aftually lofe, or acquire, any 

 weight, upon acquiring an additional quantity of latent heat. 



My fufpicions refpeiFting the accuracy of the balance arofe from a knowledge, — which 

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



The three principal points of the balance having been determined, as nearly as podible, 

 by meafurement, the axes of motion were firmly fixed in their places, in a right lii;e, 

 and the beam being afterwards finifhed, and its two arms brouglit to be in equilibrio, the 

 balance was proved by fufpending weights, which before were known to be exactly 

 equal, to the ends of its arms. 



If with thefe weights the balance remained in equilibrio, it was confidered as a proof 

 that the beam was juft; but, if one arm was found to preponderate, the other was 

 gradually lengthened, by beating it upon an anvil, until the difference of the lengths of 

 the apms was reduced to nothing, or until equal weights, fufpended to the two arms, 

 remained in equilibrio ; care being taken, before each trial, to bring the two ends of 

 the beam to be in equilibrio, by reducing, with the file, the arm which had been 

 lengthened. 



Though, in this method of conftrufting balances, the moft perfefl equality in the 

 lengths of the arms may be obtained, and confequently the greateft poflible accuracy, 

 when ufed at a time when the temperature of the air is the fame 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 fame length, one of them may be much more hammered than the other, I fu{- 

 peftcd it might be poflible that the texture of the metal forming the two arms might 

 be rendered fo fer different, by this operation, as to occafion a difference in their ex- 

 panfions with heat ; and that this difference might occafion a fenfible error in the balance, 

 when, being charged with a great weight, it fhould be expofed to a confiderable change 

 of temperature. 



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

 above related, arofe in any degree from this caufe, I had only to repeat the experiment, 

 caufing the two bottles A and B to change places upon the arras of the balance ; but, as 

 I had already found a fenfible difference in the refults of different repetitions of the fame 

 experiment, made as nearly as poffible under the fame circumftances, and as it was 

 above all things of importance to afcertain the accuracy of my balance, I preferred 

 making a particular experiment for that purpofe. 



My fir ft idea was, to fufpend to the arms of the balance, by very fine wires, two 

 equal globes of glafs, filled with mercury, and, fuffering them to remain in my room 

 till they fliould have acquired the known temperature of the air in it, to have removed 



them 



