ee ee 
SE 
On Electro-Dynamic Induction. 241 
tection the same as that of the primary current. In other cases the 
magnetism was either imperceptible or minus. With an arrange- 
ment of two coils of wires around two glass cylinders, one within 
the other, the same effect was produced. The magnetism was 
less when the distance of the two sets of spires was smaller, indi- 
cating, as it would appear, an approximation to a position of neu- 
trality. These results are rather of a negative kind, yet they 
appear to indicate the same change with distance in the case of 
the galvanic currents, as in that of the discharge of ordinary 
electricity. The distance however at which the change takes 
place, would seem to be less in the former than in the latter. 
129, There is a perfect analogy between the inductive action 
of the primary current from the galvanic apparatus and of that 
from the larger electrical battery. The point of change, in each, 
appears to be at a great distance. 
130. The neutralizing effect described in Sections IV and VI, 
may now be more definitely explained by saying that when a 
third conductor is acted on at the same time by a primary and 
secondary current (unless it be very near the second wire) it will 
fall into the region of the plus influence of the former, and into 
that of the minus influence of the latter ; and hence no induction 
will be produced. 
131. This will be rendered perfectly clear by Fig. 15, iu 
which a represents the conductor of the primary current, b that 
of the secondary, an@ c the Fig. 15. 
third conductor. The char- , Pa 
acters + + +, &c., begin- | + B 
ning at the middle of the — cea Z 
first conductor and extending ~ +e 
+ — 
downwards, represent the con- 
Stant plus influence of the 
primary current, and those + 0 — —, &c., beginning at the sec- 
ond conductor, indicate the inductive influence of the secondary 
current as changing with the distance. The third conductor, as 
is shown by the figure, falls in the plus region of the primary 
current, and in the minus region of the secondary, and hence in 
it the two actions neutralize each other, and no apparent result 
is produced. 
132. Fig. 16 indicates the method in which the neutralizing ef- 
fect is produced in the case of the secondary and tertiary currents. 
Vol. xxxvim1, No. 2.—Jan.-March, 1840. 3} 
