Compression of Air and other Gases. 



225 



Captain Schwendsen and I having proposed to investigate 

 the theory of the air gun, found it necessary to examine, as 

 a fundamental principle, the extent of the law of Mariotte. 

 The apparatus commonly employed to establish this law, con- 

 sists of a bent tube ABCD, Fig. 13, Plate V. of which DE 

 contains the air, and the other ABCE mercury, which serves 

 to inclose and to compress the air. This apparatus has seve- 

 ral inconveniences. It is difficult to divide accurately the 

 portion DE into parts of equal capacity, and this portion is 

 dilated by the interior pressure so as to expose the apparatus 

 to the risk of being broken when the pressure becomes consi- 

 derable. In order to guard against that accident, tubes of 

 a small diameter have been used, but they occasion friction 

 sufficiently great to produce a sensible influence on the re- 

 sults. 



In order to avoid these inconveniences, we had recourse to 

 an apparatus constructed according to the same principle 

 which I employed in my apparatus for the compression of water. 

 A vertical section of this apparatus is represented in Fig. 14, 

 where ABCD is a strong glass cylinder with a brass cover 

 AC ; EF is a divided glass tube (supported by an iron frame 

 I m n o) the lower part of which is an iron vessel, containing a 

 little mercury, which closes the tube EF before its immersion 

 in the mercury which is found at the bottom of the cylinder ; 

 IK is the superior limit of the mercury; Gil represents part 



VOL. IV. NO. II. Al'lllL 182G- ? 



