256 LOCALIZED ELECTKIZATION. 



upon its current, but is scarcely appreciable upon that of the 

 second coil. The outer tube, on the contrary, acts chiefly on the 

 currents of the second coil. This experiment affords an explana- 

 tion of the difference in the influence exerted by the two tubes 

 upon the rapidity and energy of the beats of the trembler. We 

 can understand that, the magnetization of the iron core being 

 produced by the current of the first coil, this magnetization must 

 be more enfeebled by the inner tube, which acts specially upon that 

 current, than by the outer tube, of which the influence upou the 

 primary current is almost nil. I shall hereafter point out the im- 

 portance of knowledge of this phenomenon. 



The apparatus with a double graduator tube, and with a double 

 movable iron core (fig. 55) will serve to repeat the whole of these 

 experiments. 



If it be desired to study the influence of the outer tube B upon 

 the currents, the inner tube C is drawn completely out from the 

 coil, as in fig. 55. The outer tube is similarly drawn off when it 

 is desired to experiment only with the inner one. 



A very simple mechanism suffices to unite the two tubes so 

 that they move together, and cover or uncover simultaneously 

 the internal and external surfaces of the coil. It follows that the 

 induction currents are then more completely neutralised than 

 when the tubes act separately. Lastly, the iron core itself being 

 movable, it is easy to experiment on the action of the tubes 

 alternately or simultaneously, either with or without the assistance 

 of the magnetic force. 



To recapitulate : 1. A tube of copper, sometimes called a dia- 

 phragm, placed in the interior, or at the exterior, of a reel, formed 

 of a primary and of a secondary superposed coil, and within which 

 there is no core of soft iron, neutralises the currents in proportion 

 as it covers more and more of the spirals, and operates as a closed 

 conductor. 2. The external tube acts specially upon the current 

 of the second coil, while the internal tube affects principally that 

 of the primary coil, 3. The tubes diminish in the same degree 

 the intensity of the currents of the primary and secondary coils, 

 when moving together in the same direction, as when acting separ- 

 ately. 4. The presence of a core of soft iron within the reel in no 

 way modifies the power of the tubes to neutralise the intensity of 

 the currents ; for if, on the one hand, the magnetic influence of the 

 iron upon the coils augments this intensity, on the other they 

 neutralise it proportionately, and as well as when the iron core is 

 absent. 5. The magnetization of the iron core is very little 

 diminished when the tubes cover the coils ; from which we may 

 conclude that the tubes act directly upon the currents of the coils. 



