254 LOCALIZED ELECTRIZATION. 



A second accident led me to tlie discovery that a slit tube lost 

 its influence upon the current of the coil that it enclosed. The 

 metal cap of the little instrument, mentioned above, was too tight 

 to glide easily over the coil, and I split it down its entire length. 

 I found that it no longer graduated the current. 1 paid no atten- 

 tion to this phenomenon, which I attributed solely to the vicinity 

 of the metallic plate ; but I soldered to one of the extremities of 

 the tube a very fine copper wire, which reunited its edges, and its 

 properties were immediately almost entirely restored. 



I made several other experiments, from which I found that, the 

 greater the distance between the coil and the walls of the tube, 

 thus mended by the wire, the less was the iufluence of the latter. 

 I concluded that, in order to obtain a maximum of diminution 

 by the metallic tube, it must be as nearly as possible in contact 

 with the coil. 



The external tube, however, did not completely neutralise the 

 induced currents ; and, indeed, when it covered the coil entirely, 

 the latter still possessed a very notable force, such that, if the 

 instrument was one of great power, this force would still be very 

 considerable. It was a matter of necessity to graduate this 

 remaining force, on which the external cylinder exerted no 

 action. 



It then occurred to me to try tlie effect of a second tube of 

 copper, made to slide in the interior of the coil, and covering or 

 uncovering the bundle of soft iron wire. The excess of induction 

 current which had not been neutralised by the external tube was 

 considerably diminished, in this experiment, by the influence of 

 the internal tube ; and, when I withdrew the latter slowly, I felt 

 the power of the current increase in proportion. To discover which 

 of the two tubes exerted the greatest neutralizing influence, I used 

 them alternately, and compared their effects upon the power of in- 

 duction. I found tliat the inner tube diminished, much more than 

 the outer one, the physiological powers of the currents of both the 

 primary and the secondary coil. It might have been expected that 

 when the inner tube was once completely inserted, the outer tube 

 would no longer influence the induced current ; but this was not so, 

 for I found that the considerable power possessed by the current 

 when the internal tube was in situ, was very sensibly diminislied, in 

 proportion as the external tube was pushed over the coil. 



In all these experiments I had not observed that the magnetiza- 

 tion of the bundle of iron wire forming the core of the coil had 

 been diminished in proportion to the diminution of the physio- 

 logical power of the induced currents. Thus, a compass being 

 placed at a given distance from the extremity of the coil, in such 



