440 Chronicles of Science. [July, 



Daniel, Professor of Physics at the Central School of Arts. It is 

 generally admitted that the current of the pile moves in the inter- 

 polar circuit from the positive to the negative pole. The existence 

 of a mechanical action exerted in this direction is confirmed by the 

 movement produced in the carbon by the voltaic arc. It is evident 

 also from the difference of level which takes place under the influence 

 of a current, in a vessel divided into two compartments by a porous 

 diaphragm, and enclosing a liquid of weak conductivity, which at 

 the commencement of the experiment presents two surfaces of equal 

 height at each side of the separation. The movement of the liquid, 

 by the current discovered by Porret, has been examined by Messrs. 

 De la Piive, Becquerel, and latterly by Windemann, who has 

 determined its laws under certain conditions. It is possible to place 

 in evidence this action of electricity, and to show the direction by 

 an experiment more simple than the preceding. M. Daniel fills. 

 with slightly acidulated water, a glass tube of any length, and of a 

 diameter from ten to fifteen millimetres, bent at a right angle at its 

 two extremities. He introduces into the liquid column a globule of 

 mercury two or three centimetres long, and immerses the electrodes 

 of a more or less powerful pile into the two vertical portions. By 

 means of the globule of mercury the instrument is easily levelled. 

 As soon as the current passes the globule becomes elongated and 

 begins to move ; going from the positive to the negative pole. If 

 by means of a commutator interposed in the circuit, the direction 

 of the current be changed, the globule stops and immediately takes 

 an opposite direction, always from the positive to the negative pole. 

 By properly moving the commutator, we can make the mercury 

 take an indefinite alternating motion. The ends of the globule 

 under the influence of the current do not present the same appear- 

 ance. It is brilliant towards the negative electrode, and dull 

 towards the positive one. This is owing to its possessing positive 

 tension in front and negative tension behind. The oxide of mercury 

 formed during the experiment is collected at the negative end, and 

 is reduced, at least in part, by the hydrogen produced at the 

 same time. If the liquid contain too much acid, a salt is formed 

 which affects the transparency of the liquid, and bubbles of 

 hydrogen are disengaged. 



When the direction of the current is altered, a sort of veil 

 which covers one of the extremities of the globule is seen to fly to 

 the other extremity. Four Bunsen elements suffice for this experi- 

 ment, if we employ a tube 0*40 m. to 0*50 m. long. With twenty- 

 four elements we can operate upon a tube a metre long. The 

 current of fifty elements gives too great a velocity to the mercury, 

 and breaks it up into globules which travel in the same direction. 

 When the tube is inclined the mercury can still move from the 

 lower to the upper end. Thus the weight of the mercury being 



