THE ATMOSPHERE. 67 



hundred and seven hundred and fifty pounds to the 

 square inch. But in the instruments of Mr Stewart, 

 this pressure has been very much exceeded. And we 

 believe he has produced greater condensation in the 

 chamber than any who has preceded him. 



The experiments of Bernoulli and Count Rumford, 

 resulted in their belief that the force of ignited powder 

 was at least ten thousand times greater than that of the 

 ordinary pressure of the atmosphere. 



According to the smallest calculation, we perceive 

 before these forces can be equal, a pressure of at least 

 fifteen thousand pounds to the square inch must be 

 produced by compressed air. 



MATCH SYRINGE. 



The match syringe consists of a simple hollow cylin- 

 der, closed at one end, and a solid piston movable its 

 whole length. Its object is suddenly to compress the 

 air contained in the cylinder, and render its heat sensi- 

 ble. The assertion that much heat exists in the atmos- 

 phere is proved by this condensation. For by com- 

 pressing the air to a very small space, the particles of 

 heat are brought into so close contact, as to set fire to 

 an inflammable substance fixed in the bottom of the 

 piston. The material generally employed, is a piece of 

 dry lint which has been previously dipped into a solution 

 of saltpetre. The piston, armed with this, being sud- 

 denly driven to the base of the barrel, is immediately 

 thrown back by the elasticity of the air, and exhibits the 

 intended effect. 



A singular result of this compression is continually 

 shown in the ordinary changes of the atmosphere. Some 

 might suppose that the wind which comes down from a 

 snow-covered mountain, would excite the sensation of 

 great cold. But they must recollect that the density of 

 the air on the earth and on the mountain, is very differ- 

 ent. A cubic foot of air on the ground, contains twice 

 as much heat as a cubic foot at three miles and a half 

 from the earth. And consequently, the air which de- 

 scends is gradually increasing in density, and becomes 

 of a similar temperature by mechanical compression. 



