Wakelin. — On the Cause of Gravitation. 126 



the plank transversely against the current, especially with its face fair 

 against the stream, the force required would be very much greater. The 

 water acts only on the outsides of the plank. If we hold the plank above 

 * the ground in any other way the " gravific " current of sether will carry it 

 to the earth with exactly the same force or weight in whatever position it 

 may be held. This supposed cm-rent does not act then only on the outsides 

 of the plank ; it must act on every particle of it. The ethereal current must 

 flow through the plank as a current of ah" would flow through a sail made 

 of netting. Every central body would in this case be a reservoh', into 

 which the sether rushes with very great rapidity. 



Let us apply this notion of a current to the case of a planet and its 

 satellite. The attraction is mutual between them ; there must therefore be 

 a current flowing, in space, from the planet to its satellite, and another 

 ffithereal current at the same time flowing from the satellite to its planet. 

 The currents would therefore oppose each other, and one would be 

 destroyed. The attractive power would be reduced, and the larger body 

 would not move at all towards the smaller ; we cannot therefore consider 

 gravitation to be caused by currents. 



The notion, however, of a current of extremely attenuated gas flowing 

 through a solid, helps us very considerably in our conception of what is 

 required. If the aether could be stationary, and act like a current, this 

 kind- of- current theory would account for gravitation. Clothes are run 

 through two elastic-rollers of a mangle. If the rollers are made to revolve, 

 and the clothes are brought within their grip, the clothes acquke the 

 velocity of the rollers. If, between the same two rollers, we place a long 

 bar of smooth steel, and the rollers be adjusted so as to press lightly on 

 the bar, they will make many revolutions before the bar acquires a per- 

 ceptible motion. It seems as if a medium that would act on every particle 

 of matter, as these rollers act on the bar of steel, would produce the gravi- 

 tational motion of bodies. We might at once suppose that revolving 

 spheres of matter, as of the common india-rubber balls, would be sufiicient. 

 If the spheres revolve and come in contact with matter under a very small 

 pressTU'e, the matter they are in contact with would begin to acquire the 

 motion of this revolving shell. As one side moves one way, and the other 

 side the opposite way, the body would not move from its place, whatever 

 other motion it might acquire. These revolving spherical shells are then 

 insufficient. 



Let us take a piece of gutta-percha, or india-rubber tubing, of a suit- 

 able length, say eight to twenty times the diameter of the tube. Let this 

 tube revolve exactly as the rollers of a mangle revolve, and let the velocity 

 of rotation be increased to any necessary degree. As the rate of rotation 



