between Mercury Surfaces. 



Fio-. 3. 



487 



A W-tube, 0*8 centim. diam., was made 

 up as in fig. 3 ; mercury in the two lower 

 parts, acidulated water in the junction c, and 

 platinum wires in tbe outer limbs. On tilt- 

 ing the tube, so that tbe surface in a advanced 

 and tbat in b receded, tbe mercury in «, by- 

 reason of tbe sligbt friction, flowed, of course, 

 less readily in contact witb tbe glass tban 

 at tbe centre ; and so fresb surface broke 

 through. On the other side (b) just the 

 reverse took place ; whatever suboxide was 

 on the sides closed in and thickened. 



The needle of the galvanometer between the platinum wires 

 was deflected in one direction when the system was inclined 

 one way, and when it was inclined the other way, in the other 

 direction. The advancing surface brightened and was posi- 

 tive to the receding surface, which became duller. 



Tube inclined from Excursion of 



light-point. 



Upright to left + 125 divisions. 



,, „ right -125 „ 



Right „ left +185 „ 



Left „ right —187 „ 



Upright „ left +118 „ 



» n right -115 „ 



Right „ left +180 „ 



Left „ right —175 „ 



The same was done with capillary tubes, and the effect found 

 to be still more striking, whether the tube was tilted or the 

 mercury caused to travel along by increasing the pressure of 

 the air above one of the ends. 



Then a straight length of capillary tube turned up at the 

 ends and attached to mouth-pieces was filled with mercury, 

 in the middle of it being a small quantity of acid water. 

 When this was tilted or otherwise so that the acid water tra- 

 velled along, an electromotive force was obtained equal to 

 nearly one third of a Daniell element. 



An ordinary U-tube had mercury poured into the bend to 

 about an inch up each limb ; acid water over this, and plati- 

 num wires in the acid water. When at rest, a small constant 

 electromotive force was observed. When tilted, results pre- 

 cisely similar to those with the W-tube were found. With 

 capillary tubes provided with enlarged ends, the effects were 

 the same, and due unquestionably to the same cause. 



