56 Electric Currents on the Earth, 



establish the fact, that " while the quantity of water carried 

 away from the tropical sea is greater than that which rain 

 and rivers give back to that sea, the reverse takes place in 

 the polar seas, where the evaporation is very small, and the 

 condensation of vapour very great." Therefore, if my views 

 be correct, the earth is similar to a vast hydro-electrical ma- 

 chine. The vapour, with its electricity, rising at the equator, 

 is carried over towards the frigid regions where the vapour 

 falls, and its electricity escaping to the earth, rushes along its 

 surface towards the equator, and is again taken up by the 

 rising vapour. This circulation of electricity would go on un- 

 interruptedly during the summer, or at all times when the 

 air in the frigid regions is sufficiently damp to conduct the 

 electricity from the vapour or clouds to the earth ; but when 

 the air in these regions is very dry during severe frosts, 

 these currents are interrupted by the escape of the electricity 

 from the vapour being prevented, when the electricity accu- 

 mulating in the region of the clouds, would exhibit the phe- 

 nomena of the aurora, either by flashing back through the 

 upper and rarer air towards the equatorial or more temper- 

 ate regions, or, by the accumulation of more vapour, charged, 

 either more or less, with electricity, causing an electrical dis- 

 turbance, through the whole mass of vapour by the rush of 

 electricity to gain its equilibrium. 



That the aurora is connected with the formation of clouds, 

 the observations of Parry, Franklin, Hood, Richardson, and 

 others, have satisfactorily proved. The fall of minute parti- 

 cles of snow during an aurora in the zenith, tends to prove 

 this, and also the theory of the electrical suspension of va- 

 pour. Dr Richardson says it is by no means an uncommon 

 occurrence after an aurora has continued for some hours, 

 and is about to disappear, but the particles are so fine that 

 they are more readily felt on the face than seen. 



I believe that the circulation of these hydro-electrical cur- 

 rents is connected with the phenomena of terrestrial magnet- 

 ism ; and the fact that all ferruginous matter lying in the 

 line of the magnetic meridian becomes in time magnetised, 

 tends to prove it, especially when it is borne in mind that a 

 needle is rendered magnetic by a shock of electricity passing 



