the possibility of producing a great mechanical effect at a distance. 

 This invention is, of course, fundamental to the operation of electrical 

 systems of all kinds: telephone, telegraph and electric power. 



7 . Non-inductive Winding {1835) 



Both Henry and Faraday devised non-inductive windings in con- 

 nection with their experiments on self induction. Henry's publication 

 was, however, slightly earlier than Faraday's. The non-inductive 

 windings so described are fundamentally the same in principle as 

 those now used for resistance coils and other apparatus where self 

 inductance is reduced to a minimum. 



It is interesting to note that before the discovery of self induction 

 Faraday constructed for use in certain experiments on mutual induc- 

 tion an apparatus closely parallel to the non-inductive winding, 

 namely, two closely associated secondary windings connected in series 

 opposing. 



8. Transformer {1838) 



While both Faraday and Henry used a transformer structure in their 

 first mutual induction experiments, it was only later (1838, published 

 1839) that it was discovered by Henry that by the proper proportioning 

 of the coils the \-oltage could be stepped up or stepped down with this 

 structure. This is fundamentally the basis of modern electrical 

 transformers. 



9. Electromagnetic Shielding {1838) 



Henry discovered the screening effect of all good conducting sub- 

 stances interposed between two coils, i.e. the primary and secondary 

 of a transformer. After publishing his results Henry learned of 

 Faraday's results published at about the same time purporting to show 

 that this screening effect did not exist except with magnetic materials. 

 Henry thereupon explained the reason for this apparent discrepancy 

 and reaffirmed his own results. 



He also pointed out that this principle has an important bearing on 

 the improvement of electrical machinery, and explained the advantage 

 which had been found by using bundles of wires instead of solid pieces 

 of iron, i.e. lamination. 



10. Discoveries Bearing Particularly on Radio Telegraphy and Telephony 



{1838 to 1842) 

 Henry (1838, published 1839) showed the variation in current 

 induced in a secondary circuit as the separation between primary and 

 secondary is varied. This is the principle of the variometer widely 

 used in radio work. 



