256 Prof. Rijke on some Properties of the Induced Current, 





Medium in which the rupture 



of the inducing circuit took 



place. 



Greatest striking distance. 





millims. 



8-6 

 33-6 

 576 











I worked with, ordinary rain-water, the jet was produced by a 

 pressure of about 10*5 millims. The electrodes were the same 

 knobs of copper as those used in the preceding experiment. 



10. It has been sufficiently established by many physicists, 

 that when an induced current is passed through the wire of a 

 multiplier, the deflection obtained is quite independent of the 

 mode in which the interruption is effected. It is simply neces- 

 sary that the rupture takes place in a space of time very short 

 compared with an oscillation of the magnetic needle. It has been 

 concluded that the quantity of electricity which the interruption 

 of the primary current sets in motion in the induced wire remains 

 the same, whatever be the manner in which the rupture is made, 

 for example in the middle of a flame. Does not this increase of 

 the striking distance appear to prove that, when the rupture takes 

 place under these conditions, what is called the electromotive 

 force of the induced wire experiences a more or less considerable 

 increase? There is always the same quantity of electricity; it 

 simply takes less time to traverse the circuit. But if this is the 

 case, it follows that, when the multiplier is replaced by a Weber's 

 electrodynamic dynamometer, the deviation of this instrument 

 must increase. In fact this instrument only differs from an 

 ordinary galvanometer in having the magnet replaced by a 

 moveable helix suspended in the interior of the multiplier by 

 two wires very near each other. The apparatus being so arranged 

 that the current traverses successively the multiplier and the 

 helix, it follows that the action exerted by the multiplier on the 

 helix will be proportional to the square of the intensity of the 

 current, and that, if the duration of this current is very small 

 as compared with that of an oscillation of the helix, the elonga- 

 tion obtained will be proportional to the square of the intensity 

 of the current, and inversely as its duration. Hence, if the same 

 quantity of electricity traverses the dynamometer in different 

 spaces of time, and while it lasts the intensity of each current 

 remains constant, the elongation observed (which I assume to 

 be very small) will be inversely as the time which the current 

 will have taken in traversing the dynamometer, or, in other 

 terms, directly as its electromotive force. This elongation is 

 measured very accurately by MM. Poggendorff and Gauss's 



