128 Prof. J. C. Poggendorff on the Indue tivn Apparatus 



guished from the regiilav beat of the hammer. On the contrary, 

 by employing a strong galvanic current, these sparks are quite 

 visible ; they are more steady than the interruption sparks^ emit 

 a very clear light, throw out smaller sparks, and, \Yith conden- 

 sers of small dimensions, assume the appearance of a small flame 

 breaking forth from under the hammer. This is a consequence 

 of the great intensity of the current, which has also the eflect of 

 fusing the platinum extremity of the hammer, even when the 

 same is 1 millim. thick, and soldering it to the anvil, so that the 

 action of the instrument is arrested unless the small electro- 

 magnet has sufficient power to overcome the solder. The latter 

 always occurred when a current from one of Grove's elements 

 was conducted through the wire 400 feet long and two-thirds of 

 a millim. thick. 



Riess found that this fusion could be avoided by using a long, 

 thin, German silver wii-e to connect the condenser with the 

 hammer, and thus throwing a body of great resistance into the 

 circuit. The discharge sparks, however, are thereby merely 

 weakened; they can still be observed by employing the current 

 from a l)attcry of two elements, even when 120 or 130 inches of 

 German silver wire, 0'45 millim. in thickness, are introduced 

 between the condenser and the hammer by means of the rheo- 

 chord, and it is at the same time indifferent whether the current 

 traverses the wires of the primary coil side by side or one after 

 the other. 



Further, the action of the condenser upon the induction cur- 

 rent is weakened by so great a length of German silver wire, as 

 may be best seen by the luminous phfenomena in the electric 

 egg. This is most perceptible when the wires of the primary 

 coil are traversed side by side ; when they are arranged one after 

 the other, no diminution in the action can be detected, even 

 when 150 inches of German silver wire are used. In the latter 

 case, however, where the interruption at the hammer is scarcely 

 perceptible, the luminous phajnomenon in the egg is, without a 

 condenser, somewhat different to what it is in the first case ; it 

 is more compact, and more like that which is caused by the ad- 

 dition of a condenser. 



The interruption sparks as well as the discharge sparks attack 

 the hammer strongly, and pulverize the parts which beat against 

 one another to a black powder. It is a remarkable fact, which 

 has never yet been sufficiently reconciled with the action of a 

 pm'e voltaic current, that here, where an induction current (an 

 extra current) also acts, the negative pole is most heated, and 

 that a transfer of platinum from this to the positive pole is the 

 consequence. li the platiman end of the hammer be connected 

 with the negative or zinc pole of the battery, and the tongue vi^ith 



