536 Prof. J. C. Poggendorff on a new Electrical 



'&o 



of an induction-coil 10,000 feet in length, without perceiving a 

 decrease in the action. Just as little effect is produced by a 

 shunt, if it is not too strong. The electrodes to which the tube 

 hangs, if they terminate in points, may be brought within an 

 inch from each other (when small sparks begin to pass) without 

 causing the cessation of the phenomenon of motion in the tube. 



Even the current of an ordinary electrical machine with a disk 

 of only 15 inches set the mercury just as briskly in vibratiou 

 as that of Holtz's machine ; the motion was not, however, so 

 continuous, but was more by starts. And it was the end of the 

 machine joined with the conductor (that is, with the positive 

 pole of the machine) towards which the mercurial thread moved. 



I also produced the phenomenon with a Holtz's machine in 

 conjunction with a Leyden jar. The tube was suspended with 

 one end to the positive electrode, and with the other to an 

 insulated brass stand to which the negative electrode was ap- 

 proached within about half an inch. It was interesting to ob- 

 serve that sometimes before a spark of the jar passed, therefore 

 while the positive electricity flowed through the electrode in the 

 formation of this spark, the mercury in the tube began to move 

 towards the positive pole, or, rather, towards the more positive 

 part of the positive electrode, and when the spark passed remained 

 almost stationary. 



An induction-current appears to act like the current from the 

 machine, but, in spite of its great quantity, far more feebly than 

 the latter. I have been unable to arrive at certain conclusions 

 in the matter. In order to avoid the injurious influence which 

 platinum wires, under the influence of the induction-current, 

 exert upon mercury, I had made six exhausted mercurial tubes 

 provided with aluminium wires. With the current of the ma- 

 chine all of them produced good effects, though not so good 

 as the tube mentioned before ; but a powerful induction-cur- 

 rent had only a doubtful action, in spite of the fact that it filled 

 them with a white stratified or granulated light visible in day- 

 time, none of which appeared with the current of the machine*. 

 In the tube which I have mentioned, and which I did not like 

 to expose to an induction-current, with several discharges the 

 mercury jerked every time towards the positive side. 



In this phenomenon the quantity of electricity is less im- 

 portant than what is called intensity or tension ; and it is thereby 



* Aluminium wires cannot, however, be recommended for these tubes. 

 In a few days the mercury in these tubes loses its mobility, becomes vis- 

 cous, drawn out into threads, adhering in parts to the glass, and therefore 

 incapable of showing distinctly the phenomenon of motion. Tubes with 

 platinum wires are not exposed to this deterioration, provided they are not 

 exposed to an induction-current. 



