MEMOIR XXVI.] CAPILLARY ATTRACTION, ETC. 351 



take place between the protuberant tide on the mercury 

 and the wire. At that moment the cause of attraction 

 is annihilated, the whole current of electricity now pass- 

 ing along perfect conductors, and fulfilling the supposed 

 case of an annihilation of the sun and moon at the time 

 of high tide. And the same reasoning that held in one 

 case applies equally in the other the mercurial tide falls 

 with an accelerated motion, and the line which before 

 was the transverse axis of the ellipse becomes the conju- 

 gate, tides being produced at right angles to the former 

 ones. But here the strict comparison ends, for as the 

 mercury ebbs from its protuberant position the metallic 

 connection breaks, and the wire is again put in action as 

 a point of attraction. The motion of the ebbing tide is 

 checked ; it flows once more. Once more the metallic 

 contact is complete ; and when the tide falls, it is only to 

 flow again as long as the battery current passes. Tides 

 take place at right angles to each other, in a series too 

 rapid to be counted, and the whole surface of the mer- 

 cury is worked into those various and beautiful undula- 

 tions which have been before referred to. 



With respect to the currents that are observed, as if a 

 gentle wind were playing over the surface, the explana- 

 tion is obvious. We have seen that when a voltaic cur- 

 rent is passed through mercury and water, the pressure 

 on the surface of contact is changed. Newton has shown 

 (" Principia," Vol. II., Bk. ii., Pr. 41) that if the particles 

 of a fluid do not lie in a right line, a pressure propagated 

 through that fluid will not be in a rectilinear direction, 

 but the particles that are obliquely 

 posited have a tendency to be urged 

 out of their position. So the particles 

 a, a, Fig. 77, pressing on the particles 

 #, d, which stand obliquely to them by Fig - 7T - 



reason of the shape of the mass of mercury, M, have a 



