1824.] Conductors when transmitting the Electric Current. 173 



10. That friction against the vessel is the principal cause of 

 the apparent attraction of a globule of mercury to the negative 

 end, may be proved evidently by the substitution of a glass for 

 a Wedgwood-ware basin. In this case the currents are pro- 

 duced as before ; but, though equally forcible, the globule 

 shows little or no tendency to move bodily, but if placed on a 

 plate of emeried glass, or on any other rough surface, it will 

 move with great activity ; nay, so strong is its tendency to the 

 negative pole, that globules of considerable magnitude may 

 thus be sustained without contact of either wire, on surfaces* 

 many degrees inclined to the horizon. 



11. It is essential to the production of the motions in ques- 

 tion, that the mercury be in actual contact and free communi- 

 cation with the acid, and so situated as to be within the in- 

 fluence of the electric current. It is not necessary, however, 

 that a continuity of the acid should subsist between the posi- 

 tive and negative wires ; they will appear in any interrupted 

 circuit of mercury and the liquid medium. The experiment 

 indeed is difficult to try in sulphuric acid, whose capillary 

 attraction for mercury is such that the least drop, applied to 

 any part of a clean surface of that metal, instantly spreads over 

 the whole, but with other conducting media it may readily be 

 made. We have only to drop a little of the liquid to be tried 

 on two different spots of a large clean surface of mercury, and 

 bring the poles in contact with them, taking care not to plunge 

 them in the metal, when the same phamomena will be observed 

 to take place about each pole as if the whole surface had been 

 covered with the liquid. The motions however are confined to 

 such portions of the mercury as are actually covered, all the 

 rest remaining quite still : the effects too are modified by capil- 

 lary action. 



12. When the circuit is completed in a conducting liquid, in 

 the manner described in the beginning of this paper, the action 

 is most forcible in the direct line joining the poles ; its violence 

 diminishing as we recede from this line, though it continues 

 sensible to a great distance either way : and the course pursued 

 by electricity in its passage through conducting media, and its 

 law of distribution within it, may in some degree be traced, by 

 placing globules of mercury in different parts of a liquid; when 

 it will be plainly seen, that it is by no means confined, or nearly 

 so, to the straight line between the poles, or to the surface of 

 the conducting medium, but immediately on quitting the wires 

 diffuses itself through the whole liquid, its density being a 

 maximum in the space directly between them, and diminishing 

 rapidly as we recede from their line of junction. 



13. The mechanical action appears (ralcris paribus) to be 

 proportional to the absolute quantity of electricity which passes, 

 iluh) tempore, through a filament of the liquid at the point 



