1835, and published in the Philosophical Transactions of that year, 

 described the non-inductive winding as follows: 



"Thus, if a long wire be doubled, so that the current in the two halves shall have 

 opposite actions, it ought not to give a sensible spark at the moment of disjunction: 

 and this proved to be the case, for a wire forty feet long, covered with silk, being 

 doubled and tied closely together to within four inches of the extremities, when used 

 in that state, gave scarcely a perceptible spark; . . . ."'-'* 



Prior to this discovery Faraday in 1832 had constructed for use in 

 certain experiments on mutual induction an apparatus closely parallel 

 to the non-inductive winding, namely, two secondary windings twisted 

 about each other to associate them as closely as possible and then 

 wound in the form of a helix. With these windings connected in 

 series opposing, he found no mutual inductive effect.^^ 



8. Transformer 

 In Henry's article, "On Electro-Dynamic Induction," read Novem- 

 ber 2, 1838, and published the following year, after referring to Fara- 

 day's discovery of mutual induction he stated: 



"Since then however attention has been almost exclusively directed to one part of 

 the subject, namely, the induction from magnetism, and the perfection of the magneto- 

 electrical machine: and I know of no attempts, except my own, to review and extend 

 the purely electrical part of Dr. Faraday's admirable discovery." ^' 



The experiments bearing on the transformer he partially summa- 

 rized as follows: 



"This experiment was considered of so much importance, that it was varied and 

 repeated many times, but always with the same result; it therefore establishes the 

 fact that an ' intensity ' current can induce one of ' quantity,' and, by the preceding experi- 

 ments, the converse has also been shown, that a 'quantity' current can induce one of 

 'ititensity.' " ^^ 



9. Electromagnetic Shielding 



Both Henry and Faraday made extensive experiments of the effect 

 of non-magnetic shields on induction between primary and secondary 

 coils. That the important screening effect was observed by Henry 

 seems to have been due to his method of observation which indicated 

 instantaneous or peak voltages, in contrast to Faraday's which gave 

 only a measure of the total quantity of induced electric displacement. 



Prior to his work on electro-magnetic shielding, Henry knew^ of the 

 discovery of magnetic rotation by Arago and of the various experiments 

 by Herschel, Babbage and Harris. These experiments had shown that 

 a revolving magnet gives rotation to metallic discs or needles suspended 



"^^Experimental Researches in Electricity by Michael Faradav, \'ol. 1, paragraph 

 1096. 



-^ Experimental Researches, Vol. 1, paragraph 194. 

 30S\V, Vol. 1, p. 114. 

 3iS\V, Vol. 1, p. 118. 



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