Intelligence and Miscellaneous Articles, 483 



means of the globule of mercury the apparatus may be easily 

 levelled. 



As soon as the current passes, the globule elongates and begins 

 to move ; it goes from the positive to the negative pole. If, by 

 means of a commutator, the direction of the current be inverted, 

 the globule stops, and immediately resumes its march, always, 

 however, from the positive to the negative pole. By suitably 

 manipulating the commutator, an oscillating motion may be im- 

 parted to the entire mass of the mercury. 



The globule thus acted upon by the current differs in appearance 

 at the two ends : it is brilliant at the positive electrode, and tar- 

 nished towards the negative one. This arises from the circum- 

 stance that, like the whole liquid column, it is polarized, and has 

 negative tension at one end and positive at the other. Oxide of 

 mercury, formed during the experiment, is carried to the negative 

 end, and is reduced, at any rate partially, by the hydrogen which is 

 produced at the same time. If the liquid contains too much acid, 

 a salt is formed, which diminishes the transparence of the column, 

 and bubbles of hydrogen are disengaged. When the direction of 

 the current is changed, the kind of veil which covers one end of the 

 globule changes its position and passes to the other end ; there is 

 still a carriage of matter, indicating a mechanical action in the con- 

 trary direction to that which produces the motion of the mercury ; 

 but on the globule this moves still from the positive towards the 

 negative end. 



Four Bunsen's elements are sufficient for the experiment, if a 

 tube of 40 to 50 centims. in length be used. With twenty-four 

 elements a long column of mercury can be moved in a tube a metre 

 in length. A current of fifty elements imparls to this column too 

 considerable a velocity ; it divides into globules, all of them moving 

 in the same direction. 



The tube being inclined, the mercury may even move from the 

 lower to the upper part of the tube. The weight of the mercury 

 being known, a tolerably correct idea can be formed of the force of 

 that portion of the current which traverses the globule. If the in- 

 clination be gradually increased, a point is attained at which equili- 

 brium is established between the force of the current which tends 

 to raise the mercury, and the action of gravity which tends to make 

 it descend ; the globule does not move, but it remains elongated ; it 

 has always an internal motion, and frequently turns upon itself, 

 first in one direction, and then in another. 



The same experiment may be made by means of Ruhmkorff's 

 coil ; but as its currents are alternately in opposite directions, an 

 interruption must be made, so as to suppress the inverse current. 

 The circuit traversed by the direct current consists then of me- 

 tallic wires, of a layer of air, and a column of liquid. When the 

 apparatus works, the globule of mercury begins to move ; it marches 

 by starts, the more marked the less frequent the breaks, and it 

 always goes from the positive towards the negative pole ; it is 

 always brilliant at one end and tarnished at the other. 



