= .* 
On Electro-Dynamic Induction. 149 
galvanometer would be produced. If these inductions are not 
precisely equal, then, only a partial neutralization will take place, 
and the shock will only be diminished in power ; and, also, per- 
haps, the needle will be very slightly affected. 
84. If, in the foregoing exposition, we throw out of considera- 
tion the actions of the feeble currents which cannot pass the 
body, and, consequently, are not concerned in producing the 
shock, then the same explanation will still apply which was 
given in the last paper, (III, 94,) namely, in the above example, 
the helix is acted on by the minus influence of the secondary, 
and the plus influence of the interposed current. 
85. We are now prepared to consider the effect on the helix 
(Fig. 3) of the induced currents produced in the conductor of the 
primary current itself. These are true secondary currents, and 
are almost precisely the same in their action as those in the inter- 
posed plate. Let us first examine the induced current at the be- 
ginning of the primary, in the case of a long coil and a battery 
of a single element; its action on the helix may be represented 
by the parts of the curve, Fig. 20. The first part, AB, will pro- 
duce an intense induction opposite to that of the primary current ; 
and hence the action of the two will tend to neutralize each 
other, and no shock, or a very feeble one, will be produced. The 
ending action of the same induced current, which is represented 
by BD, restores to the helix the same quantity of current elec- 
tricity (but in a feeble state) which was neutralized by AB, and 
hence the needle of the galvanometer will be as much affected 
as if this current did not exist. These inferences perfectly agree 
with the experiment given in paragraph 19. In this, when the 
ends of the interposed coil were joined so as to neutralize the 
induced current in the long conductor, the shock at the beginning 
of the primary current was nearly as powerful as with a short 
conductor, while the amount of deflection of the galvanometer 
Was unaffected by joining the ends of the same coil. 
86. At first sight it might appear that any change in the appa- 
tatus which might tend to increase the induction of the primary 
current (16) would also tend to increase, in the same degree, the 
adverse secondary in the same conductor; and that hence the 
heutralization mentioned in paragraph would take place 
in all cases; but we must ject that if a more full current 
be suddenly formed in a ocmaietce of a given thickness, the ad- 
