122 Prof. J. C. Poggendorff on the Induction Apparattis 



lity with which it is here produced, even without any insulation 

 of the galvanometer, will appear somewhat remarkable. 



According to Riess, a thermic action is produced in the wire of 

 the interrupted current, but it is an exceedingly weak one. With 

 my less sensitive air-thermometer I could not detect this action, 

 although the same was sufficiently sensible to show the increase 

 of heat in the perfectly closed wire, especially when the latter 

 was thick. It is worthy of notice, however, that notwithstanding 

 this, a thermo-electric battery was charged in exactly the same 

 manner as with a galvanic current, that is to say, opposite to the 

 direction of the same. I observed it in a combination of two 

 V-formed bismuth and antimony pairs. The common thermo- 

 electric batteries are not here applicable, in consequence of their 

 imperfect insulation. 



The sparks at the point where the current is broken have also 

 a thermic action, in fact, a much greater one than that which 

 takes place in the metallic circuit of the current. When very 

 thin platinum wires are used as poles, and when they are brought 

 near one another, it has already been observed by several phy- 

 sicists that the point of the negative wire, which is then sur- 

 rounded by the positive sparks, becomes red-hot. 



Chemical decompositions, decompositions of water, iodide of 

 potassiimi, &c., are effected in exactly the same manner as with 

 a galvanic current, i. e. only one electrolyte is separated at each 

 pole. In water the electrodes become polarized; and when they 

 are composed of very thin platinum wires, the negative one 

 becomes slightly illuminated at the extremity. 



Many of these decompositions are interesting when they are 

 so made that the point where the current is broken is at the 

 liquid itself. For this purpose the wires of the discharger are 

 placed vertical and near one another, and the liquid is made to ap- 

 proach them from below, so that the sparks may be made to strike 

 the liquid from both wires at once, or only from one, the other 

 being kept immersed. In general it is found that the stream 

 of sparks from the positive pole possesses a yellow or reddish- 

 yellow colour at the top, close to the point of the wire, and forms 

 a blue disc below on the surface of the water; whereas the 

 stream of sparks from the negative pole is blue at the top, and 

 surrounds with this light a part of the wire from the point, 

 whilst a yellowish glimmer rests upon the liquid. When the 

 liquid is placed nearer to the wires, about a quarter of a line 

 from them, the phsenomenon reduces itself to blue sparks at 

 the negative, and yellow ones at the positive pole. 



Further, the phfenomenon is different according to the nature 

 of the liquid. Non-conducting liquids, such as turpentine, do not, 

 of course, show the phaenomeiion at all. With distilled water it is 



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