63 



(Professor Elliot's) experiment ou the iron ring to that of 

 Saturn, but agreed with him in maintaining that Laplace's 

 hypothesis of a load on the ring Avas untenable. Pro- 

 fessor Elliot briefly described two other experiments 

 which he had himself made in regard to rotation. One 

 of these consisted in magnetizing the axis of a light 

 rotating disc, carefully depriving the disc of all pre- 

 cessional movement, inclining its axis a little from the 

 vertical line, placing over its centre an electro-magnet, 

 and then giving to the disc a rapid rotation on its axis. 

 The axis remained at rest in its oblique position till an 

 electric current was passed along the wire of the electro- 

 magnet ; as soon as that was done the axis ot the disc 

 began to revolve round the magnet. When the current 

 was transmitted in the opposite direction, the direction 

 of revolution immediately changed, producing a singu- 

 larly close resemblance to that mysterious phenomenon, 

 electro-magnetic rotation. The other experiment con- 

 sisted in taking a very large cylindrical vessel of water, 

 making a small orifice in the centre of the base, with a 

 straight brass pipe extending a few inches downward, 

 the outer end of the pipe being closed with a plug, and 

 the inner end being made perfectly smooth. The vessel 

 Avas filled with water, and as soon as that had attained 

 perfect repose the plug was withdrawn. This being- 

 done, as the level of the water sank, it gradually ac- 

 quired a rotatory movement, at first vevj slow, but be- 

 coming more rapid as the evacuation proceeded, and 

 always in the direction of the earth's rotation, provided 

 that perfect stillness of the fluid had been secured. The 

 rationale of the process was this : That the vessel of 

 water participated in the earth's diurnal rotation; its own 

 motions consisting of a revolution round the earth's axis 

 and a slow rotation on its own axis, that the portions 

 near the circumference had a n)ore rapid motion in rota- 



