54 Electric Currents on the Earth, 



The decimation of the needle seems totally inexplicable on 

 this hypothesis, and the influence of the aurora on terres- 

 trial magnetism, especially in high latitudes, also seems to 

 tell against the theory. 



As regards the theory that there are electrical currents 

 from the frigid regions to the equator, it is proved by Volta's 

 and other experiments, that whenever evaporatio i takes 

 place, the vapour carries off positive electricity, leaving the 

 water negatively charged. The experiment of Professor 

 Faraday, on the electricity of steam, from which he was led 

 to conclude, that no electrical development could take place 

 from the evaporation of a saline mixture, and that evapora- 

 tion is not the cause of the electricity of the atmosphere, tell 

 against the theory ; but the conclusions of Pouillet on the 

 electrical phenomena of evaporation are directly the reverse ; 

 for, although he agrees generally with Dr Faraday on the 

 phenomena of the electricity of steam, he " has demonstrated 

 that the conversion of pure water into vapour, at any tem- 

 perature, is not attended with any disturbance of the electric 

 equilibrium, but that vapour, rising from solutions, however 

 weak, gives signs of electricity, varying in kind, according to 

 the nature of the substance dissolved. From saline or acid 

 solutions, the vapour carries up a charge of positive electri- 

 city, and leaves the solution in a state of negative electricity ; 

 and the rule was verified particularly with regard to solutions 

 of sea-salt." The experiments of Armstrong and Pattison, 

 on the electricity of steam, were with boilers without any 

 arrangement for causing friction, and without regard being 

 had to the purity of the water. 



The experiment of Mr Pattison shews the vast quantity of 

 electricity caried off by vapour, as he says, — '' I repeated 

 Volta's experiment, by placing a hot cinder upon the cap of 

 a gold-leaf electrometer, and projecting a few drops of water 

 upon it, when the leaves diverged strongly with negative 

 electricity. I observed that when the cinder was very hot, 

 and the production of the steam consequently very rapid, the 

 electricity given out was always most powerful. 



*'I then insulated an iron pan, 12 inches diameter and 



