.Oi?^ WEIGHTS OF GASES. 197 



employed in this weighing are now to be com- 

 pared with those used in the former weighing; 

 their difference being the weight of the air or 

 gas contained in the instrument. 



Since the above paper was read before the 

 society, an instrument, similar to the one above 

 described, has been constructed, with a view of 

 ascertaining, experimentally, what good or bad 

 qualities it would be found to possess. 



When the instrument, in an exhausted state, 

 was tried in water, much difficulty was expe- 

 rienced in preventing the water from entering. 

 The experiments, in this respect, required at all 

 times the greatest care, as the smallest drop 

 getting by any means into the instrument would 

 vitiate the whole experiment. The balancing of 

 the instrument in the water was likewise found 

 to be a tedious operation, as it always made a 

 considerable number of oscillations, upwards 

 and downwards, before it came to a state of 

 quiescence. The smallest of these oscillations 

 were made in pretty nearly the same time as the 

 largest. The friction occasioned by the instru- 

 ment passing through the water, was likewise 

 found to be considerable. Upon the whole, it 



