272 Mr. Herschel on certain Motions produced in Fluid [Oct. 



from the negative wire, the flattening of the globule, and the 

 protuberances it throws out in pursuit of the oppositely electri- 

 fied conductor, sufficiently indicate their existence under the 

 crust of oxide. Where this oxidation however does not happen, 

 or is prevented by the addition of a few drops of dilute nitric 

 acid, the currents from the negative wire are equally evident 

 with those from the positive, just mentioned. 



19. These however are not the only effects produced by con- 

 tact with the electrified wires. On breaking the contacts and 

 completing the circuit in the liquid, the mercury is found for the 

 most part to have acquired new properties, or lost some of its 

 former ones. A globule of four or five hundred grains of pure 

 mercury being introduced into a solution of sulphate of soda, the 

 circuit was completed in the liquid with neither pole in contact. 

 A current was produced from the negative pole. A momentary 

 contact being made with that wire, and the circuit then com- 

 pleted as before in the liquid, a counter-current was produced 

 from the positive pole, more confined in the sphere of its extent, 

 but apparently more violent in its action than that from the 

 negative. In consequence, the globule acquired the figure here 

 annexed, having a blunt elongation at z, the point nearest the 

 negative pole, and a more pointed one at c , that next the posi- 

 tive, with a kind of shoulder at a b. The film of oxide pro- 

 duced at z was thus swept towards c, but never attained beyond 



+ • 



the zone a b, where it remained stationary and constant in quan- 

 tity, being absorbed at the side next c as fast as it was produced 

 at the other. Another short contact was now made with the 

 negative wire, and, on breaking it, the currents from c were 

 found to have increased both in strength and extent, while those 

 from 2 were proportionally enfeebled, the zone of equilibrium a b 

 being thus brought nearer to g. By another contact prolonged 

 a few seconds, the negative currents were contracted within a 

 very small space around z, and by prolonging the contact a 

 little longer, its influence was totally destroyed, and a regular 

 and violent circulation from + to — established throughout the 

 whole alobule. 



