New Outlines of Chemical Philosophy. 353 



decrease gradually between the equator and the poles, po that 

 its surface will resemble two inclined planes meeting above the 

 equator, their highest part. 



^' A current of air is constantly ascending at the equator, and 

 part of it at least reaches and continues in the higher parts of 

 the atmosphere. From the fluidity of air, it is evident that it 

 cannot accumulate above the equator, but must roll down the 

 mclined plane, which the upper surface of tlie atmosphere as- 

 sumes, towards the pole. 



" As the heat in the torrid zone never differs much, the den- 

 sity, and consequentlv the height of the atmosphere will not 

 vary much. Hence the range of the barometer within the tro- 

 pics is comparatively small ; and it increases gradually as we 

 approach the poles, because the difference of the temperature, 

 and consequently of the density of the atmosphere, increases with 

 the latitude." — Thomson's Chemistry, vol. iv. p. 46. 



It is abundantly confirmed by experience, that when the che- 

 mical union between those elements and moisture is dissolved, a 

 portion of the air is reduced into its component parts, thermo- 

 gen, photogen, and water, which return again to the earth, 

 either in flashes of lightning, or in showers of rain, hail, or 

 snow. 



Metallic rods reaching above the tops of buildiirgs are known 

 to conduct electricity from the air to the earth ; and indeed, almost 

 every elevated object is a conductor when the air is highly 

 charged with those elements ; whence we may infer, that in a 

 thunder-storm, a person is much safer iu a town, than upon an 

 open plain. I am the more inclined to believe the truth of this 

 remark from some phaenomena which came under my own ob- 

 servation. 



I u'as, some years ago, riding along the sea-shore in a very 

 dark night, when it lightned very much at sea, with distant 

 thunder. A very heavy shower came on where I was, whicli 

 produced illuminations far more brilliant than can be well de- 

 scribed. 



The small end of mv v.hip, and the tips of the ears of my 

 horse, were ornamented with small lamps or globes of fire: 

 every other little projecting point about his head was orna- 

 mented in the same manner; and his mane was almost one 

 entire blaze of light. I attempted several times to extinguish 

 these lights by striking them with my whip, but without pro- 

 ducing any permanent effect ; for no sooner was the water struck 

 off from the parts v.-hich were illuminated, than these lights 

 were regenerated by the succeeding drops of rain. These illu- 

 minations continued as long as the shower lasted, which might 

 be about a ([uarter of an hour. 



Vol. 44. No. \d9. Nov. 1814. Z This 



