158 WRITINGS OF JOSEPH HENRY. [1855- 



pheres of different gases, having different densities at the 

 surface of the earth. These heights will evidently be in- 

 versely as the densities, or in other words the specific grav- 

 ities, of the same gases under the same pressure. If the 

 specific gravity of hydrogen be represented by 1, that of 

 nitrogen in round numbers will be 15, that of oxygen 16, 

 and that of carbonic acid 22, and the total heights of atmos- 

 pheres of these gases will be inversely as these numbers ; or 

 if we call the height of an atmosphere of oxygen 60, then 

 the heights of atmosphere of these gases will be as follows : 



In the foregoing the repulsive energy has been considered 

 as increasing in conformity with the law of Mariotte, directly 

 as the pressure and without regard to the increase of repul- 

 sion caused by heat; but if we suppose that the repul- 

 sion of the atoms of the lower stratum is increased by heat, 

 they will be farther separated, and the space occupied by 

 them enlarged. But if the heat extends upward through 

 the whole, each of its parts will be uniformly expanded, 

 and hence the relative height of atmospheres of different 

 grades will not be altered by an increase of heat, provided 

 this increase is the same in each gas. The absolute heights 

 will however be increased -^^ part for each degree of Fahren- 

 heit's scale above its volume at the freezing point. 



In order to obtain or determine an equilibrium of the at- 

 mosphere when the natural repulsion of the atoms is in- 

 creased by heat, each stratum as we ascend must at least con- 

 tain the same amount of caloric. In this case, if a quantity 

 of air be removed from a lower to a higher position, it will 

 expand on account of the reduced pressure, and the same 

 amount of heat being now diff"used through a larger space, 

 the intensity of its action or its temperature will fall, and 



