360 THE INTELLECTUAL RISE IN ELECTRICITY. 



force. What Descartes really had discovered was the 

 endlessness of these apparent lines of magnetic force. 



This idea of the spirals flowing in definite directions 

 through conduits in the magnet, he applies to all magnetic 

 phenomena, of which he finds therein an explanation often 

 with marvelous ingenuity. The stream of spirals flows 

 more easily through the lodestone or iron than through the 

 air or any other substance, because the conduits in the first- 

 mentioned bodies are better suited to them. Wherever 

 the streams enter and leave a body, there are its poles. If 

 a magnet, free to move, presents its conduit entrances at 

 an angle to the stream of spirals from the earth's poles, 

 the force of the stream is sufficient to turn the magnet so 

 as to bring the conduits in line with its path, and then so 

 that the north entrances of the conduits are directed to 

 the south pole of the earth, and vice versa; thus the 

 directive tendency of the needle to the poles is explained. 

 "There are always," he says, "more spirals around the 

 magnet than elsewhere in the air, because, after they have 

 left one end of the stone, they find in the air a resistance, 

 which causes most of them to return to the other end of 

 the magnet whereat they enter ; and thus several remain 

 around it, making a kind of whirlpool, the same as they 

 make about the earth. So that the whole earth may be 

 taken for a magnet not differing from others, unless it be 

 bigger : and that on its surface where we live its virtue is 

 not very strong. " Thus the field outside of the magnet 

 is accounted for and a definite conception is suggested of a 

 "resistance " to the force, compelling it to choose a certain 

 path. 



But there is still more in the foregoing quotation. If 

 the earth is so vast and great a magnet, why is its virtue 

 "not very strong?" The streams of spirals are generated 

 in the earth in a certain region, which last is a spherical 

 stratum. In passing to the earth's surface they encounter 

 another and outer stratum of metals, etc., abounding in 

 conduits suitable to them. Many of them pass through 



