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



at both ends, and passed the current through the length of the 

 tube, which, as far as possible, was placed horizontally. Here 

 I again saw a motion of the mercury, more distinct and defined 

 than before, but by no means so decisive as to justify me in say- 

 ing it was real. The case was the same with a third, fourth, and 

 fifth tube, though in the latter it assumed such a form as to con- 

 vince me that I was not labouring under a mistake. 



A sixth tube finally removed all doubt. This had been pre- 

 pared with particular care. It had not only been most carefully 

 exhausted, but the mercury in it had been kept briskly boiling 

 for some time, so that when the tube was inclined it made a 

 sharp crack in striking against the ends. The tube, moreover, 

 was bent at right angles at a distance of about an inch from each 

 end, so that the platinum wires were not touching the mercury ; 

 for I thought I had observed that the mobility of the mercury 

 (probably owing to the formation of amalgam) was diminished 

 by such a contact. 



This tube, in which the mercury was extremely mobile, was 

 hung by wire hooks to the electrodes of the machine in such a 

 manner that the middle was perfectly horizontal. This could 

 easily be effected by moving the electrodes, the mercury thread 

 itself serving as level; the adjustment was altered until it re- 

 mained at rest in a certain position of the tube, even when gently 

 struck with a stick. 



When this adjustment was effected the machine was set to 

 work. As soon as the current passed through the tube the mer- 

 cury moved, and travelled with considerable velocity from the 

 negative to the positive pole. In whatever direction the cur- 

 rent was sent the result was always the same ; I never saw an 

 exception. 



Even in the fifth tube this travelling of the mercury towards 

 the positive pole could not be mistaken ; but, owing to an adhe- 

 sion of the metal to the side of the tube, it often stuck, and had 

 to be assisted by tapping : in the last tube this was not necessary. 

 So long as the current continued, the motion was continuous 

 and easy, and could be hindered or renewed at pleasure according 

 as the current was opened or closed. 



For this mobility of the mercury, it is necessary that when 

 the tube is horizontal it does not occupy the entire section, which 

 with the width taken is either not at all the case, or only so for 

 short distances. That the tube is quite filled for a short length 

 does not do much harm; it acts just like a cork, until the free 

 thread has quite passed and taken it to the end ; but for the 

 most part I arranged the tube so that the mercury formed a 

 thread or cylinder over which the current could pass. 



In the experiment mentioned, this thread was 4 inches in 



