MAGNETIC TELEGRAPH. 43 



the magnet, it struck a small bell or sounder, 

 which spoke its signals ; and that apparatus there 

 was maintained to illustrate the telegraph to the 

 students. 



When applied to practical use, some code of 

 signals must be arranged for translating the 

 successive taps of the armature ; but that was 

 well known in the telegraphic art for ages, 

 needing only good judgment in arranging it, 

 so that the letters which occur most frequently, 

 shall be represented by the smallest number of 

 motions ; just as Gauss and Weber arranged their 

 needle-telegraph code in 1833, when the movements 

 of their needle to and fro, in a number of simple 

 combinations, indicated the alphabet.* 



These ' ' spools " of Henry have been the means 

 by which most of the great discoveries in electro- 

 magnetism have since been made. Faraday and 

 Henry used them in their famous researches already 

 referred to, in which they discovered magneto- 

 electricity. Sturgeon, in writing of them, says : 

 " Professor Henry has been enabled to produce a 

 " magnetic force which totally eclipses every other 

 " in the whole annals of magnetism; and no parallel 

 " is to be found since the miraculous suspension of 

 " the celebrated oriental impostor in his iron 

 " coffin, "f Without them we could not have the 



* See Appendix, Note S. 

 t See Appendix, Note T. 



