998 Transactions of the American Institute. 



author of one of the principal forms of magneto-electric machines, 

 says: "Having, in November, 1834, tried the effects produced by 

 coils varying in diameter, I found that the thick copper bell wire 

 gave brilliant sparks, but no perceptible shock, whilst, on the con- 

 trary, very fine wire gave powerful shocks, but very inditfereut 

 sparks. I took advantage of my discovery, and furnished my 

 machines with two armatures — one of thick wire, and one of fine 

 wire." {Lond. and Edin. Phil. Magazine for October, 1836.) 

 So far as we are able to learn. Prof. Callau was the first to adopt 

 the fine wire for the secondary coil, in combination with a coarser 

 primary wire on the electro-magnet. 



Some time in September, 1837, Prof. M'Gauley, of Dublin, 

 exhibited at the meeting of the British Association, at Liverpool, 

 an electro-magnetic coil apparatus, which though very awkwardly 

 constructed, yet embraced one very important and ingenious feature, 

 viz: an automatic circuit-breaker, which was, in one particular, the 

 type of most of the automatic circuit-breakers now in use. It, 

 however, was deficient in having no adjus'tment to vary its force. 



The next coil apparatus of Professor Page was communicated 

 under date of June 2d, 1838, for Silliman^s Journal^ and published 

 •in October following. In this machine, called the Magneto-Electric 

 Multiplier, the primary and secondary circuits were insulated from, 

 and independent of, each other, and wound upon a bundle of iron 

 wires, bent into a horse-shoe or U form. The circuit-breaker was 

 so arranged upon a shaft bearing an armature that the circuit might 

 be broken at the instant the armature required the maximum of 

 mechanical force to cause it to recede from the poles of the magnet, 

 and thus efiect the more sudden neutralization of the magnetic 

 forces and agument the intensity of the secondary. It is emphati- 

 cally said of this coil, that the " secondary is msulated from, and 

 entirely independent of, the primary." 



The next published account of induction apparatus is also one 

 of Prof. Page's. The first description of this improvement is in a 

 work published by Daniel Davis, Jr., of Boston, in November, 

 1838. The little work of seventy-two pages, though entitled a 

 " Descriptive Catalogue," is essentially a treatise upon the subject 

 of electro-magnetism and magnetic electricity. For the sake of 

 distinction, we shall call it Davis' first manual. Three pages and a 

 half arc devoted to the description and explanation of this new 

 induction coil and apparatus. It embraced two important and 

 distinctive features of construction. (See Fig. 2.) One, the auto- 



