On Electro-Dynamiec Induction. 237 
true one, since the magnetizing spiral might possibly itself, in 
some cases, induce an opposite current. 'To satisfy myself on 
this point, a series of charges, of various intensity and quantity, 
from a single spark of the large conductor to the full charge of 
hine jars, were passed through the small spiral, which had been 
used in all the experiments; but they all gave the same polarity. 
The interior of this spiral is so small, that the needle is through- 
out in contact with the wire. 
118. The fact of a change in the direction of the induced cur- 
rent by a change in the distance of the conductors, being thus 
established, a great number and variety of experiments were 
made to determine the other conditions on which the change 
depends. These were sought for in a variation of the intensity 
and quantity of the primary discharge, in the length and thick- 
hess of the wire, and in the form of the circuit. The results 
Were, however, in many cases, anomalous, and are not sufficiently 
definite to be placed in detail before the Society. I hope to re- 
Sume the investigation at another time, and will therefore at 
present briefly state only those general facts which appear well 
€stablished. : 
119. With a single half gallon jar, and the conductors sepa- 
rated to a distance less than ,',th of an inch, the induced current 
is always in the same direction as the primary. But when the 
conductors are gradually separated, there is always found a dis- 
tance at which the current begins to change its direction. This 
distance depends certainly on the amount of the discharge, and 
probably on the intensity ; and also on the length and thickness 
of the conductors. With a battery of eight half gallon jars, and 
parallel wires of about ten feet. long, the change in the direction 
did not take place at a less distance than from twelve to fifteen 
inches, and with a still larger battery and longer conductors, no 
change was found, although the induction was produced at the 
distance of several feet. 
120. 'The facts given in the last paragraph relate to the induc- 
tive action of the primary current; but it appears from the results 
detailed in paragraphs 110 and 114, that the currents of all the 
other orders also change the direction of the inductive influence 
With a change of the distance. In these cases, however, the 
change always takes place at a very small distance from the con- 
ducting wire ; and in this respect the result is similar to the effect 
of a primary current from the discharge of a small jar. 
