196 METHOD OF DETERMINING THE 



tube B, B ; the lower extremity of this tube is 

 terminated by the cock C, which opens or cuts 

 off the communication with the interior of the 

 globe A, A. This cock has on it a screw, by 

 means of which it may be connected with any 

 description of pneumatic apparatus. When the 

 instrument is placed in water, a ball of lead, D, 

 is attached to this screw, for the purpose of 

 balancing the instrument, and sinking it to a 

 proper depth. From the upper part of the globe, 

 A^ A, projects a stem, E, E, consisting of a 

 piece of wire, upon the top of which is fixed the 

 cup, F. A small hole is likewise perforated 

 through the stem E, E, as is shewn at G. 



The method of using the instrument is as 

 follows : it is first exhausted, and then, the ball 

 of lead, D, being screwed upon the cock, C, it 

 is placed in water, and small weights, consisting 

 of bits of lead, or of any other suitable material, 

 are placed in the cup, F, and increased or dimi- 

 nished until the small hole, G, through the stem, 

 E, E, is just level with the surface of the water. 

 The instrument is now to be taken out of the 

 water and filled with the gas or air the density of 

 which is to be ascertained. The ball of lead, D, 

 being replaced, it is again put into the water, 

 and sunk, by additional weights, to the small 

 hole in the stem, E, E, as before. The weights 



