by the employment of different Resistances. 525 



has already shown, when a Leyden jar is introduced into the 

 circuit. 



If, instead of introducing the test-tube into the induction wire, 

 we attach it to one end of the same and conduct the other to 

 the earth, we likewise obtain opposite currents ; or, to explain 

 myself more cautiously, negative light appears at both wires. 



If we melt into a small tube, which contains very rarefied air, 

 only one wire and then attach it to one end of the induction- 

 coil whilst the other is in contact with the earth, we obtain, if the 

 tube be freely suspended in air, a luminous appearance on the 

 above wire, which appearance is always of negative light ; the 

 tube may be in connexion with either end of the induction-wire ; 

 or, supposing it to remain at the same end, the current may 

 traverse the wire in either direction. The intensity of the light 

 is increased if we approach the tube with a conductor from the 

 outside. 



In how peculiar a manner glass influences the discharge, is 

 seen from the following observation. If the air-tube be intro- 

 duced into the wire which completes the circuit, and if its wires 

 be so far separated that only single currents circulate, whilst on 

 their being further removed from each other opposite currents 

 arise, the passage from one wire to the other ceases as soon as 

 the tube, thus arranged, is grasped with the hand; whilst in the 

 test-tube that also forms a part of the circuit, opposite currents 

 are immediately perceived. At the same time we observe (if 

 not always, it is frequently the case) that the electricity in the 

 air-tube passes to the glass. This phenomenon likewise makes 

 its appearance in the electric egg; it is necessary, however, 

 as this instrument is much wider than the tubes, to make its 

 whole circumference a conductor by means of a strip of tinfoil. 

 When we remove either the hand or the tinfoil, some time 

 usually elapses before the passage from one wire to another is 

 re-established. 



From what has been before cited it may be inferred, and expe- 

 rience conclusively confirms it, that if the distance of the polar 

 wires in the tubes, filled with water or air, be so chosen that on 

 the employment of the large induction-coil single currents are 

 still formed, then on replacing the large apparatus by the small 

 one, opposite currents make their appearance*. The resistance 



* For both apparatus one and the same contact-breaker was always 

 used, the one which Ruhmkorff makes for his large induction-apparatus. 

 With it the breaking of the contact is effected by the separation of a plati- 

 num wire from amalgam, the separation being, on Neef's principle, brought 

 about by a small special electro-magnet, whose magnetism is induced by a 

 single Daniell's element. 



The breaking of the contact by means of Neef's hammer, already men- 

 tioned, whereby a point separates from a plate, diminishes the strength of 



