MAGNETIC TELEGRAPH. 



ment. Instead of insulating the core, he wrapped 

 a fine copper wire with silk, and wound it on the 

 core; each spiral closely packed against its fellows, 

 so as to correct the spiral error as much as possible 

 in each layer; and then he wound the wire in a 

 second spiral over the first, but with the pitch of 

 the screw, so to speak, in the opposite direction. 

 And carrying out the principle he multiplied the 

 coils to an enormous extent in the same way. The 

 result justified and established his theory; and his 

 magnets at once showed a capacity hundreds of 

 times greater than any then known to science.* 



But this was not all. Another step had to be 

 taken before Barlow's demonstration could be over- 

 thrown, and the telegraph made possible. And 

 this he took by discovering and establishing the 

 fact, that a magnet with a long fine wire coil must 

 be worked by a battery of "intensity," composed 

 of a large number of cells in series, when a distant 

 effect was required; and that the greatest dynamic 

 effect, close at hand, is produced by a battery of a 

 very few cells of large surface, combined with a coil 

 or coils of short coarse wire around the magnet. 



These discoveries and inventions solved the 

 problem which had seemed to European scientists 

 insoluble; and in one account of them which was 

 published in " Sillimari's Journal" for January, 

 1831, he says : " The fact that the magnetic action 



* See Appendix, Note Q. 



