274 WRITINGS OP JOSEPH HENRY. [1855- 



tioD is from Dauiell's Chemical Philosophy, and is given as 

 an illustration of the immense motive power due to the fall of 

 a single pound of water in the form of rain. During a single 

 rain, in 1857, water fell to the depth of 6 inches in the space 

 of 36 hours, and considering merely the amount of ascen- 

 sional power evolved by the condensation of the quantity of 

 the liquid which fell on the roof of the Smithsonian build- 

 ing, it would be equivalent to a thousand horse-power ex- 

 erted during one day. 



From these considerations it is evident that the general 

 currents of the atmosphere must be very much modified by 

 the action of the vapor, and very different from those de- 

 scribed in our previous essays as belonging to dry air. In- 

 deed to such an extent are some of the general phenomena 

 influenced by this cause, that the motive power of the atmos- 

 phere has been referred to other causes than the action of the 

 heat of the sun;- but in this case, as in most other exceptions 

 to a principle deduced from a wide generalization — like that 

 of the action of solar heat on our atmosphere, the facts 

 when rightly understood and properly interpreted, serve but 

 more firmly to establish the truth. 



We shall now consider more minutely the effect of the 

 formation and condensation of vapor in modifying the gen- 

 eral circulation of the atmosphere. It has been shown in the 

 previous articles, that if the earth were at rest in space, with- 

 out revolution on its axis, heated at the equator and grad- 

 ually cooled to a minimum point toward the poles, there 

 would be a constant circulation of air from the poles, north 

 and south, toward the equator. The air would rise in a 

 belt encircling the whole earth, and flow backward towards 

 the poles above. In this simple circulation, at every place 

 on the surface of the earth, in the northern hemisphere for 

 example, there would be a perpetual wind from the north 

 flowing toward the equator, and above the same place at 

 the surface of the aerial ocean there would be a return 

 current constantly flowing from the equator toward the 

 pole. It is evident however since the meridians converge 

 and meet at the pole, that the space between any two be- 



