198 METHOD OF DETERMINING, &C. 



appeared, that the instrument was capable of 

 determining the weight of air or gases to a con- 

 siderable degree of nicety, though, perhaps, not 

 superior, in this respect to the ordinary method, 

 which has likewise the advantage of being more 

 expeditious. 



One circumstance occurred, during the expe- 

 riments, which deserves notice, and that was, 

 the extreme dehcacy with which the instrument 

 indicated variations in the density of the water, 

 occasioned by alterations in the temperature; 

 from which it appeared, that the instrument 

 might be very properly used to determine the 

 density of water, for all degrees of temperature 

 below the boiling point.* 



* Soon after the reading of the above paper, it was pointed out 

 to the author, that an instrument on a similar principle was 

 described in Dr. Desagulier's translation of s'Gravesande's Ma- 

 thematical Philosophy. This instrument consisted of a lar^e 

 irlobe of glass, having a long neck furnished with a stop cock. 

 The method of using it was as follows : — the instrument being 

 exhausted, was suspended to the end of one arm of a balance, the 

 globe itself being immersed in water, with a part of the neck and 

 the stop cock remaining above the surface. The centre of the 

 balance was now raised and lowered until the balance itself stood 

 in an horizontal position, and then the cock being opened the 

 globe became filled with atmospheric air, and the equilibrium of 

 the balance consequently destroyed. Weights were now placed 

 in the opposite scale until the equilibrium was restored, and these 

 weights consequently shewed the weight of the air admitted into 

 the instrument. 



The similarity of this instrument, with that invented by the 

 author, will be readily seen ; the original idea of both appears 

 to have been the same, viz : — that of floating the receptacle of 

 the gas in water, and by that means to relieve the balance from 

 as much of the weight as possible. 



