1821.] Phanomena of Heat y Gases, Gravitation, S^cl 343 



given portion of the Containing vessel must be augmented ; and 

 the space in which the atoms have to move being less, their 

 returns, or periods, must be shorter ; and the number of them, 

 in a given time, consequently greater, on both of which accounts 

 the elasticity is greater, the greater the condensation. Besides, 

 when other things are the same, the elastic force augments with 

 an augmentation of temperature, and diminishes with a diminu- 

 tion ; for an increase of temperature, according to our theory, 

 must necessarily be attended with an increase of velocity ; and, 

 therefore, with an increase in the number of colhsions. But 

 these things will be more accurately treated of presently. 



Whether all pressive forces be not the same as this gaseous 

 action, is a question we do not at present intend to consider. It 

 might come under our cognizance hereafter, when we shall have 

 had more opportunities of collating our principles v/ith experi- 

 ments. In the mean time it is sufficient to anticipate that our 

 inquiries, whatever be the possibility of the existence of another 

 kind of pressive force, lead us to conclude that nature operates 

 hy no other. 



It might be asked by what means is it, if the parts of the gases 

 are absolutely hard, that they are reflected back into the medium: 

 from the sides of the containing vessel ? This question is easily 

 answered, if we allow heat to consist in an intestine motion of 

 the parts of the bodies ; for then the paris of a solid, of equal 

 temperature with a gas, must have the same quantity, though 

 they have not the same freedom of motion as the parts of a gas 

 have ; and hence the parts of the gas will have the same reflec- 

 tion from the sides of the vessel that they have from one another. 



Prop. VL 



The figure of the vessel, in which a gas is contained, has no- 

 influence on the elastic force of the gas, such a constitution of 

 things being granted as we have supposed. 



For since the particles of the gas receive their reflection frono; 

 Ihe superficial particles of the containing body ; and since these 

 particles have not only their intestine motion, but likewise their 

 figure and arrangement, independent of the superficial figure of 

 the containing body, it follows, that the direction of their action 

 on the particles of the gas is also independent of the figure of the- 

 body in which they are enclosed. But other things being alike,, 

 this action is equal to the contrary action of the particles of the 

 gas, which constitutes its elastic force; therefore, its elastic 

 force is not affected by the figure of the body in which it is 

 contained. 



Cor. — Hence we gather that in any bodies of equal capacity 

 and of the same temperature, the same, or an equal portion of 

 the same gas, would be equally elastic ; for the motion of the 

 particles being independent of the figure of the containing body 

 must depend entirely upon the temperature of that body ; and 



