6 An Inquiry concerning 



other was gradually lengthened, by beating it upon an 

 anvil, until the difference of the lengths of the arms was 

 reduced to nothing, or until equal weights, suspended 

 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 a file the 

 thickness of 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 accu- 

 racy, 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 bal- 

 ance 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 two arms might be rendered so far different by this 

 operation as to occasion a difference in their expansions 

 with heat ; and that this difference might occasion a 

 sensible 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 two bottles A and B to change places 

 upon 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, I preferred making a particular experi- 

 ment for that purpose. 



