Joule. 335 



them, is somewhat simpler, I shall employ it in the 

 following remarks on the constitution of elastic fluids ; 

 premising, however, that the hypothesis of a rotary motion 

 accords equally well with the phenomena. 



' Let us suppose an envelope of the size and shape of a 

 cubic foot to be filled with hydrogen gas, which, at 60 

 temperature and 30 inches barometrical pressure, will 

 weigh 36*927 grains. Further, let us suppose the above 

 quantity to be divided into three equal and indefinitely 

 small elastic particles, each weighing 12*309 grains; and 

 further, that each of these particles vibrates between 

 opposite sides of the cube, and maintains a uniform 

 velocity except at the instant of impact ; it is required to 

 find the velocity at which each particle must move so as to 

 produce the atmospherical pressure of 14,831,712 grains on 

 each of the square sides of the cube. In the first place it 

 is known that if a body moving with the velocity of 32 

 feet per second be opposed during one second by a pressure 

 equal to its weight, its motion will be stopped, and that, if 

 the pressure be continued one second longer, the particles will 

 acquire the velocity of 32 J feet per second in the contrary 

 direction. At this velocity there will be 32 collisions of a 

 particle of 12*309 grains against each side of the cubical 

 vessel in every two seconds of time ; and the pressure occa- 

 sioned thereby will be 1 2-309 x 32^ = 395 -938 grains. There- 

 fore, since it is manifest that the pressure will be proportional 

 to the square of the velocity of the particles, we shall have 

 for the velocity of the particles requisite to produce the 

 pressure of 14,831,712 grains on each side of the cubical 

 vessel, 



7;=t/ I4)83I ' 7l2> ) 32^ = 6,225 feet per second. 



N '8 / 



