SECT, xxxv.] MAGNETISM OF THE SUN AND PLANETS. 381 



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

 when under the influence of powerful magnets, evolves elec- 

 tricity, it is probable that the gulf stream may exert a sensible 

 influence upon the forms of the lines of magnetic variation, 

 in consequence of electric currents moving 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 magnetism, that scarcely 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 combina- 

 tions probably exist, which have never yet been noticed. 



According to the observations of MM. Biot and Gay- 

 Lussac, during their aerostatic expedition, the magnetic 

 action is not confined to the surface of the earth, but extends 

 into space. The moon has become highly magnetic by in- 

 duction, in consequence of her proximity to the earth, and 

 because her greatest diameter always points towards it. Her 

 influence on terrestrial magnetism is now ascertained : the 

 magnetism of the hemisphere that is turned towards the 

 earth attracts the pole of our needles that is turned towards 

 the south, and increases the magnetism of our hemisphere ; 

 and as the magnetic, like the gravitating force, extends through 

 space, the induction of the sun, moon, and planets must 

 occasion perpetual variations in the intensity of terrestrial 

 magnetism, by the continual changes in their relative posi- 

 tions. 



In the brief sketch that has been given of the five kinds 

 of electricity, those points of resemblance have been pointed 

 out which are characteristic of one individual power. But, 

 as many anomalies have been lately removed, and the iden- 

 tity of the different kinds placed beyond a doubt by Dr. 

 Faraday, it may be satisfactory to take a summary view of 



