1825.] 



Explanation of the Theory, S^c, 



45 



H 



V 



05 



3^C 



ysr 



^T 



^ 



beinff a vacuum, and quite dry, affix 

 within it by means of the clamp T, 

 at any height above x, the cylindrical 

 weight, or piston, P, of the specific 

 gravity of mercury at 32° Fahr. and 

 restore the communication between 

 the water and the vacuum by un- 

 screwing the stopper S. (22.) The 

 temperature of the two divisions 

 being preserved uniformly and con- 

 stantly at 50° F. the elastic vapour 

 emanating from the liquid will ascend 

 through the aperture x, and instan- 

 taneously fining the chamber V, will 

 press therein in every direction with 

 a force determined solely by the 

 temperature. The vertical height of 

 the piston being 0*4 in. we may 



unclamp it, and although suffered to gravitate freely, it wilt 

 continue perfectly stationary : — a column of mercury at 32° F. 

 and of the height of 0*4 in. forming an exact counterpoise to the 

 force, tension, or elasticity, of aqueous vapour of the temp, of 

 50° F. 



(23.) Provided the temperature of the space continue at 

 50° F. the tension of the vapour therein will not be affected by 

 an augmentation of the temperature of the liquid in W. 



(24.) The weight (height) of the liberated piston being dimi- 

 nished in any ratio, the excess of force of the vapour would oblige 

 it to ascend until the elasticity of the vapour, decreasing as the 

 volume augmented, would merely support the reduced pressure; 

 but being sustained at its initial force as the space increases, by 

 continued supplies from the reservoir of water, it will succeed,, 

 if not prevented, in forcing the piston completely out of the 

 cylindrical vessel C. 



(25.) If we increase in the least degree the compressing 

 weight, and suffer it to gravitate, the whole of the vapour will 

 be condensed, and regaining in its liquid state the reservoir W, 

 will allow the piston to descend to x. 



(26.) Repeating our first experiment with a pressure equal to 

 the force of the vapour, if we compel the piston to descend by 

 degrees, we shall find that as the space diminishes, the vapour 

 occupying that space will be liquefied without affecting in the 

 least the force of the residue. The piston will consequently 

 remain stationary every time we abandon it solely to its own 

 gravitating force. 



(27.) If we diminish in any degree the temperature of the 

 space containing the vapour, a portion will repass to the liquid 

 state: th^ elasticity of the remainder will be reduced, and 



