AND EXTERNAL RESISTANCE. 309 



posed there rests a column of nitrogen gas, its 

 particles will equally recede, and become inti- 

 mately mixed with those of the oxygen gas. 

 Other gases, as caloric, or watery vapor, may be 

 thrown in, and the same arrangement of their 

 particles will take place, and thus on the 

 earth's surface, there will rest so many columns 

 of gases, each intimately blended indifferent 

 to each other each supporting itself by its own 

 elastic power, and the inferior strata of each 

 only pressed by their own incumbent weight. 

 It is owing to the ignorance of the difference 

 which exists between expansibility and elasti- 

 city, that many have been led to contend, that 

 unless two fixed points existed, it was impossi- 

 ble for expansible bodies to expand ; the fact 

 is unquestionably true, with respect to elastic 

 bodies as they are called, but not with respect to 

 those that are expansible, expansible bodies 

 manifest their power without them -elastic bo- 

 dies derive the whole of their power from them. 

 A piece of steel, is only elastic through the me- 

 dium of compression at both ends. Air is expan- 

 sible at all points. The steam of water does not 

 derive its expansible force from the resistance 

 which it overcomes, from the sides of the kettle 

 in which it is enclosed the steam possesses 

 this expansible power without their influence; 

 it is the pressure of the steam which is able 



