100 WRITINGS OF JOSEPH HENRY, [1835 



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 1 believe still remains an 

 isolated fact. When a current is transmitted through a wire, 

 and a number of small needles are placed transverse 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 increases, until it becomes zero ; the polarity 

 of the needles is then inverted, acquires a maximum, de- 

 creases to zero again, and then resumes the first polarity; 

 several alternations of this kind being observed.* Now this 

 is precisely what would take place if we suppose that the 

 principal current induces a secondary one in an opposite 

 direction in the air surrounding the conductor, and this 

 again another in an opposite direction at a great distance, 

 and so on. The needles at different distances would be acted 

 on by the different currents, and thus the phenomena de- 

 scribed be produced. 



The action of the spiral is also probably connected with 

 the fact in common electricity called the lateral discharge: 

 and likewise with an appearance discovered some years since 

 by Nobili, of a vivid light, produced when a Leyden jar is 

 discharged through a flat spiral. 



The foregoing views are not presumed to be given as ex- 

 hibiting the actual operation of nature in producing the 

 phenomena described, but rather as the hypotheses which 

 have served as the basis of my investigations, and which 

 may further serve as formulae from which to deduce new 

 consequences to be established or disproved by experiment. 



Many points of this subject are involved in an obscurity 

 which requires more precise and extended investigation ; we 

 may however confidently anticipate much additional light 

 from the promised publication of Mr. Faraday's late re- 

 searches in this branch of science. 



*Cumming's Demonferrand, page 247 ; also Edinburgh Journal of Science, 

 October, 1826. 



