Nbtu OittUnes of Chemical 'Philosophy. 43 1 



produces no light ; and the moon produces abundance of light 

 v.'ithout any sensible heat. 



On the Elecindhj of the Earth. 

 It is well known to every electrician, that the electrical ma- 

 chine acts much more powerfully at one time than at another, 

 but the cause of these variations does not seem to be clearly im- 

 derstood. It has been generally supposed, that this ij owing Jo 

 the state of the atmosphere ; that the air may be too moist or 

 loo dry for electrical experiments ; or that the machine may be 

 out of order. But as the Levden phial cannot be charged un- 

 less it have communication with the ground, it may therefore 

 be supposed that the action of the maciiine is influenced by the 

 electrical state of the earth. Many ingenious instruments have 

 been invented for determining the electricity of the atmosphere, 

 but the electricity of the earth has been much less attended to, 

 and therefore much less understood : this may have been owing 

 to the want of appropriate instruments. 



By an extensive series of experiments, I find that the electri- 

 city of the earth is as variable as that of the atmosphere ; but 

 my experiments are too few (amounting only to about a thou- 

 sand) to determine the exact quantitv of it. I may, however, 

 venture to state, that when the earth is very dry it contains very 

 little electricity, but after heavy showers of rain it is generally 

 found very strongly electrified. 



'' In Lima, where there is no rain, they never have any light- 

 ning or thunder ; and, as M. Tournefort was assured, it never 

 rains in the Levant but in winter, and that is the only season 

 in which anv thunder is heard." — Phil. Trans, abr. vol. xii. 

 p. 661. 



" The mean amuial quantitv of rain at Granada, Antilles, 

 12^ N. is 126 inches*," (= 10 ft. 6 in.) and if the greater portion 

 of this water rises again into the atmosphere, after the rainy 

 season is over, immense quantities of electricity must be carried 

 up with it. Hence the thunder and lightning, tornadoes, hur- 

 ricanes, and tempests, are much more dreadful and frequent in 

 the torrid zone than in colder climates, where the quantity of 

 water and electricity which rises into the atmosphere by evapo- 

 ration, and falls again to the earth in rain, is much less. 



On the ElectricitTJ of the Atmosphere. 



That the atmosphere contains much more moisture and elec- 

 tricity at one time than at another, is well known ; and that 

 electricity descends to the earth from the clouds in hail, rain, 

 or snow, has been ascertained by various experiments. But 



♦■ Phil. Miig. vol. xliv, p. 350. 



liow 



