352 Nhv Outlines of Chemical Philosophj, 



Water being 914 times heavier than an equal bulk of atmd- 

 spheric air, it will be easily conceived, that when the oxygen antl 

 hydrogen gases, contained within a circle of many miles in dia- 

 meter, are reduced into water, an immense vacuum must be in- 

 stantaneously formed ; and, conseijuentlv, the air rushing into i€ 

 must produce a violent concussion, accompanied -with a tremen- 

 dous report. 



Hence the reason that the wind blows towards a thunder 

 cloud ; and a freslv portion of oxygen gas being thus r.oixed with 

 the hydrogen gas which remains imconsumed, a second reporS 

 succeeds the first ; and thus thunder will be continued as long as 

 any hydrogen gas remains un consumed. 



The extent of the influence of the two elements upon each 

 other to decompose the air, may be estimated, in some degree, 

 by the breadth of the shower : not by its length, for that may 

 be influenced by the wind. 



The quicksilver falls in the barometer during a thunder storm^ 

 because the atmosphere is lighter, part of it having been con- 

 verted into a heavy shower of rain ; but when the shower is 

 over and evaporation recommencing, the water being again con- 

 verted into air, the atmosphere becomes heavier and the quick- 

 silver rises. When the chemical union between water and the 

 two elements of combustion is dissolved, those elements descen(i 

 to the earth with the falling rain ; hence the reason that the air 

 becomes colder after a shower ; and the reai^ion that we have no 

 thunder in a rainy season is this ; the elements of combustion 

 are conducted back again to the earth, as fast as they ascend 

 into the atmosphere. 



If the mean ainiual quantity of water Avhich rises by evapora- 

 tion be ccjual to the mean annual quantity of rain, there musE 

 be ten feet six inches of water converted into atmospheric aie 

 annually, in the lat. of 12° N. and therefore it might be sup- 

 posed that the barometer vv'ould rise higher and its range be 

 greater at the equator than in higher latitudes : but it is novv» 

 known from experience, that the range of the barometer is leas'! 

 at the equator and increases as we approach the poles. This 

 seeming contradiction, however, will vanish after the following 

 extracts have been duly considered.- 



*' The mean height of the barometer at the level of the sea, 

 all over the globe, is ;J0 inches, the weight of the atmosphere, 

 therefore, is the same all over the globe. The weight of the 

 atmosphere depends on its density and height : v/here the den- 

 sity of the atmosphere is greatest, its height must be the least ; 

 and on the contrary, where its density is'^least, its height must 

 be the greatest. The height of the atmosphere, therefore, must 

 be greatest at the equator and least at the poles 3 and it must 



decrease 



