1 66 Mr. Herschel on certain motions produced in 
returning would be equal, and the centre of gravity of the 
whole mass would remain at rest ; but by reason of the fric- 
tion and adhesion of the fluid metal to the vessel and liquid, 
these re-act on the globule in a direction contrary to that of 
the superficial currents, and the centre of gravity accordingly 
advances in that direction, or towards the negative pole. 
When this motion cannot take place, the internal current, 
having all one uniform direction, forces its way outwards 
to the negative pole, distorting and elongating the figure of 
the mercury in proportion to its energy. If the metal be 
oxidated, so as to give a certain tenacity to the superficial 
film, the radiating currents pursue their course under it; 
and the supernatant fluid, being thus defended from their 
action, remains at rest. In this case the only indication of 
their existence is the protuberance produced by the resultant 
interior streams. 
9. A number of singular appearances are explained by this 
internal current. In some cases the mercury throws out pro- 
jections or probosces of inordinate length, which take the di- 
rection of the electrified wire, and follow all its motions. The 
resultant interior current is in this case directed along the 
axis of the proboscis from its root to its extremity, which 
thus becomes an indication of a very powerful radiation along 
its surface in an opposite direction. In others, the mercury 
flattens throughout its whole extent, and, when this is the 
case, it is always covered with a thick coat of oxide. In these 
circumstances the superficial currents tend from the circum- 
ference towards the centre of the flattened mass, and the in- 
terior stream tends from the centre outwards in all directions. 
