Capillary and Electrical Phenomena. 289 



lute electromagnetic measure 



23223000 x 4-5 x Q55 _ 12927 

 q ~ 78xJL0 10 x57 "" 10 10 ' 



To make this clearer we may call- to mind that, according to 

 Weber, the electrical equivalent of water is 0098 milligr. 

 Hence an increase of surface of 1 square millim. would disen- 

 gage a quantity of electricity which would decompose almost 

 130 milligrammes of water. 



In order to have the deflections proportional to the quantities 

 of electricity, the currents must, of course, have an infinitely short 

 duration compared with that of the swing of the needle. With 

 this view the reservoir of mercury was provided with a cock, 

 which was only opened for a short time after a complete raising 

 or lowering. Moreover small displacements were employed; 

 for the current requires an appreciable time if, with a given 

 glass tube, the displacement of the mercury exceeds a certain 

 amount, because with this length the resistance of the thin 

 layer of acid between the glass and the mercury, and which 

 forms a part of the circuit, becomes larger, and the discharge 

 slower. 



The same electrical currents may also be very simply pro- 

 duced. A glass vessel contains mercury and dilute sulphuric 

 acid. A glass funnel filled with mercury is so adjusted that its 

 lower very fine aperture dips in the acid. -If the two masses of 

 mercury (that in the glass vessel and that in the funnel) are 

 respectively connected with the terminals of a galvanometer, the 

 needle is deflected as long as the flow of mercury continues. The 

 extension of surface of each drop as it forms causes the produc- 

 tion of the current. 



The funnel may be replaced by a drawn-out tube, and the 

 vessel by a second similar tube, and thus the simple electromotor 

 of fig. 4 may be constructed. The mercury then flows through 

 both tubes ; when the stationary condition has been attained, the 

 deflection of the needle remains constant. 



Polarization by Capillary Forces. 



If, after the metallic contact between the poles a and ft has 

 been broken, the mercury be displaced, we have the ordinary 

 condition of things ; for hitherto no attempt has been made to 

 complete an electrical circuit in capillary experiments. Pheno- 

 mena are then observed of which a portion are known as " un- 

 explained disturbances." If the reservoir A is raised (that is, 

 the surface in M increased), and at the same time the pole ft 



Phil. Mag. S. 4. Vol 47. No. 312. April 1874. U 



