132 
the shock was feeble. With a double wire spool (one within the 
other) of 2650 yards, placed above the primary coil (having about 
the same weight as the copper ribbon), the magnetizing effects dis- 
appeared, the sparks were much smaller, ‘ but the shock was almost 
too intense to be received with impunity.’’’ * Evidently, the in- 
duced secondary in this case was a current of great ‘‘ intensity ’’ 
and of proportionately small ‘‘ quantity.’’ Hence these experi- 
ments showed that it is possible to induce an intensity current from 
one of quantity and a quantity current from one of intensity, a 
principle underlying our modern induction coils and transformers. 
Further, Henry used the secondary induced current as an initial 
current, and so induced from it a tertiary current. ‘‘ By connect- 
ing the secondary coil with another at some distance from the pri- 
mary, so as not to be influenced by it directly, but forming, with 
the secondary, a single closed circuit, not only was the distant coil 
capable of producing, in an insulated wire helix placed over it, a 
distinct current of induction at the interruption of the primary, 
but sensible shocks were obtained from it.’’ ‘By a similar but 
more extended arrangement, shocks were received from currents of 
a fourth and a fifth order; and, with a more powerful primary cur- 
rent and additional coils, a still greater number of successive in- 
ductions might be obtained.’’ ‘It was found that, with the small 
battery, a shock could be given from the current of the third order 
to twenty-five persons joining hands; also shocks perceptible in 
the arms were obtained from a current of the fifth order.’’ + As 
Henry, himself, remarks, ‘‘ The induction of currents of different 
orders of sufficient intensity to give shocks could scarcely have been 
anticipated from our previous knowledge of the subject.’’ By in- 
geniously introducing a small magnetizing helix into each circuit, 
Henry found that the direction of these successive currents was 
alternately reversed with reference to each other. 
It was while endeavoring to repeat these successive inductions by 
means of ordinary electricity that Henry was led to one of his most 
important discoveries. His apparatus consisted of an open glass 
cylinder, about six inches in diameter, provided with two long 
narrow strips of tin foil pasted around it in corresponding heliacal 
courses, one of these strips being on the outside and the other on 
the inside, directly opposite to the first. The extremities of the inner 
* Memorial of Professor Henry, p. 247. 
+ Trans. Amer. Philos, Sozc., Vol. vi (N. S.), p. 308, 1888, 
