SiG PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR 



as matliematically 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. If a 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 

 svidden 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 phaenomenon 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 phaenomenon 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 diff"erent 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 



