Strr. XXXV. EARTH MAGNETIC BY ROTATION. 333 



direction with that of the hands of a watch, the current 

 of electricity flows from its center to the circumference ; 

 and when the rotation is in the opposite direction, the 

 current sets the contrary way. The greatest deviation 

 of the galvanometer amounted to 50 or 60, when the 

 direction of the rotation was accommodated to the oscil- 

 lations of the needle. Thus a copper plate, revolving in 

 a plane at right angles to the line of the dip, forms a new 

 electrical mnchine, differing from the common plate- 

 glass machine, by the material of which it is composed 

 being the most perfect conductor, whereas glass is the 

 most perfect non-conductor ; besides, insulation, which 

 is essential in the glass machine, is fatal in the copper 

 one. The quantity of electricity evolved by the metal 

 does not appear to be inferior to that developed by the 

 glass, though very different in intensity. 



From the experiments of Dr. Faraday, and^lso from 

 theory, it is possible that the rotation of the earth may 

 produce electric currents in its own mass. In that case, 

 they would flow superficially in the meridians, and if 

 collectors could be applied at the equator, and poles, as 

 in the revolving plate, negative electricity would be col- 

 lected at the equator, and positive at the poles ; that is 

 to say, there would be a deficiency at the equator and a 

 redundancy at the poles ; but without something equiv- 

 alent to conductors to complete the circuit, these cur- 

 rents could not exist. 



Since the motion, not only of metals but even of fluids, 

 when under the influence of powerful magnets, evolves 

 electricity, it is probable that the gulf-stream may exert 

 a sensible influence upon the forms of the lines of mag- 

 netic variation, in consequence of electric currents mov- 

 ing across it, by the electro-magnetic induction of the 

 earth. Even a ship, passing over the surface of the 

 water in northern or southern latitudes, ought to have 

 electric currents running directly across the line of her 

 motion. Dr. Faraday observes, that such is the facility 

 with which electricity is evolved by the earth's magnet- 

 ism, that scarce any piece of metal can be moved in 

 contact with others without a development of it, and 

 consequently, among the arrangements of steam-engines 

 and metallic machinery, curious electro-magnetic coin- 



