THEY PRODUCE TIDES. H 



28. The doctrine which I wish to establish from this experiment is, that though the 

 polar wires are plunged in a conducting medium, and the current is actually passing, 

 yet they still act as centres of attraction. The motions of mercury and other fluids are 

 only exemplifications of this doctrine. 



29. When a spheroidal mass of conducting matter is brought in presence of a point 

 of attraction, situated at a distance from its surface, the particles on that surface will be 

 differently affected as their situation in regard to the attracting point varies. Thus, on 

 touching the mercurial globule, named in the first part of this paper, with a negative 

 wire, and introducing into the water a positive platina pole, the globule, w T hich before 

 was spherical, becomes ellipsoidal, two tides are formed upon it, one directly opposite 

 the positive wire, and the other 180 degrees from it ; meanwhile there is an ebb in those 

 regions which are situate a quadrant from the point of attraction. If the positive wire 

 is made to revolve round the globule, both tides move, always keeping the same rela- 

 tive position to the point of attraction that they had at first It only requires the force 

 of the battery to be appropriately moderated to exhibit these phenomena with the ut- 

 most rigiduess. And as these motions exhibit very nearly, on a small scale, that effect 

 which takes place on an immense scale by the joint action of the Six and MOON hi 

 producing the tides of the ocean, I have given them the name of Tidal motions of mo- 

 vable Conductors. 



30. Now the mechanism which produces the change of figure from a sphere to an 

 ellipsoid is sufficiently obvious. We have two forces under consideration : 1st. The 

 cohesion or grav itation of the mercurial particles upon each other ; and, 2d. The dis- 

 turbing force of the polar wire as a centre of attraction. As that disturbing force de- 

 creases in a certain ratio, as the distances increase, the mercurial particles on the side, 

 A (Jig. 8, pi. 1), nearest to the polar wire are more attracted by it than those in the cen- 

 tre, C, of the globule, and those in the centre, C, are more attracted than those at F. 

 The particles, therefore, at A rise towards the wire by its direct action, those at F being 

 less solicited towards the centre of the globule than those at E and B ; the former re- 

 cede from that centre, while the latter seek it. 



31. It has been observed that a true theoretical tide differs in no respect from a wave- 

 " Suppose a spring tide actually formed on a fluid sphere, and the sun and moon then 

 annihilated, the elevation must sink, pressing the under waters aside, and causing them 

 to rise where they were depressed. The motion will not stop when the surface comes 

 to a level, for the waters arrive at that position with a motion continually accelerated. 

 They therefore pass that position, as a pendulum passes the perpendicular, and will 

 rise as far on the other side, forming a high water where it was low water, and low 

 water where it was high water. And this would go on forever, oscillating in an as- 

 signable time, if it were not for the viscidity of the water." Now this theoretical case 

 mav be easily shown, for on approaching the positive wire towards the globule of mer- 

 cury, a particular position will be gained, at which contact will take place between the 

 protuberant tide on the mercury and the wire. In that moment the cause of attraction 

 is annihilated, the whole current of electricity now passes along perfect conductors, 

 hence fulfilling the supposed case of an actual annihilation of the sun and moon at the 

 time of spring tide. And the same reasoning that held in one case, equally applies in 



