546 PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR 
as mathematically investigated by Cavendish, Poisson, and others. When 
the two wires A and B are in their natural state, an equilibrium is 
sustained by the attractions and repulsions of the two fluids in each 
wire; or, according to the theory of Franklin and Cavendish, by the 
attractions and repulsions of the one fluid, and the matter of the two 
wires. Ifa current of free electricity be passed through A, the natural 
equilibrium of B will be disturbed for an instant, in a similar manner 
to the disturbance of the equilibrium in an insulated conductor by the 
sudden addition of fluid to a contiguous conductor. On account of the 
repulsive action of the fluid, the current in B will have an opposite 
direction to that in A; and if the intensity of action remains constant, 
a new state of equilibrium will be assumed. The second state, how- 
ever, of B may perhaps be regarded as one of tension; and as soon as 
the extra action ceases in it, the fluid in B will resume its natural state 
of distribution, and thus a returning current for an instant be pro- 
duced. 
The action of the spiral conductor in producing sparks is but another 
case of the same action; for since action and reaction are equal and in 
contrary directions, if a current established in A produces a current in 
an opposite direction in B, then a current transmitted through B should 
accelerate or increase the intensity of a current already existing in the 
same direction in A. In this way the current in the several successive 
spires of the coil may be conceived to accelerate, or to tend to accelerate 
each other; and when the contact is broken, the fluid of the first spire 
is projected from it with intensity by the repulsive action of the fluid in 
all the succeeding spires. 
In the case of the double spiral conductor, in experiment sixth, the 
fluid is passing in an opposite direction ; and according to the same 
views, a retardation or decrease of intensity should take place. 
The phenomenon of the secondary shock with the battery appears 
to me to be a consequence of the law of Mr. Faraday. The parts of 
the human body contiguous to those through which the principal cur- 
rent is passing, may be considered as in the state of the second wire B; 
when the principal current ceases, a shock is produced by the returning 
current of the natural electricity of the body. 
If this explanation be correct, the same principle will readily account 
for a curious phenomenon discovered several years since by Savary, but 
which I believe still remains an isolated fact. When a current is trans- 
mitted through a wire, and a number of small needles are placed trans- 
verse to it, but at different distances, the direction of the magnetic 
polarity of the needles varies with their distance from the conducting 
wire. The action is also periodical; diminishing as the distance in- 
creases, until it becomes zero; the polarity of the needles is then in- 
verted, acquires a maximum, decreases to zero again, and then resumes 
