180 ANNUAL OF SCIENTIFIC DISCOVERT. 



it had been described more than twenty years before by Mr. Sang, nor was 

 it iu his (Professor Elliot's) opinion practically successful in showing the 

 earth's rotation, since its success depended altogether upon the adjustment 

 of the apparatus; and the only mode, he believed, of making that very 

 delicate adjustment was by trying it if it produced the very motion it was 

 intended to demonstrate. It could be made to show the rotation of the 

 earth, or not shoAV it, just as it was balanced. Professor Smythe's apparatus 

 he had previously described. Professor Maxwell, of Aberdeen, was the last 

 who had produced anything new on the subject of rotary motion, and in a set 

 of beautiful experiments and some refined calculations, he had advanced fur- 

 ther into the subject than any of his predecessors. Professor Maxwell's prin- 

 cipal object was to throw r light on the theory of Saturn's ring, for his essay 

 on which he lately had the high honor of gaining the Adams Prize offered 

 by St. John's College, Cambridge, for the best dissertation on that subject. 



Professor Maxwell objected to the applicability of his (Professor Elliot's) 

 experiment on the iron ring to that of Saturn, but agreed with him in main- 

 taining that Laplace's hypothesis of a load on the ring was untenable. 



Professor 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 disk, carefully depriving the disk of all proces- 

 sional movement, inclining its axis a little from the vertical line, placing over 

 its centre an electro-magnet, and then giving to the disk a rapid rotation on 

 its axis. The axis remained at rest in its oblique position till an electric cur- 

 rent was passed along the wire of the electro-magnet. As soon as that was 

 done the axis of the disk began to revolve around the magnet. When the 

 current was transmitted in the opposite direction, the direction of revolution 

 immediately changed, producing a singularly close resemblance to that mys- 

 terious 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 was filled with 

 water, and as soon as that had attained perfect repose the plug was with- 

 drawn. On this being done, as the level of the water sunk, it gradually 

 acquired a rotary movement, at first very slow, but becoming more rapid as 

 the evacuation proceeded, and always in the direction of the earth's rota- 

 tion, 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 more rapid motion in rotation than those near the 

 centre. In approaching the centre they retained their actual velocity, and, 

 consequently, increased in angular velocity, and in escaping at the central 

 orifice, produced a vortex in the direction of the earth's rotation, affording 

 another experimental pi-oof that such rotation existed, 



Mr. Higginson apprehended that when the iron pole of the instrument 

 was not itself a magnet, the action of the magnet was the same as that pro- 

 duced by suspending a weight to the equatorial part of the instrument. 

 When a movable magnet, turned upside down, was supplied, there would be 

 repulsion. It would act as if the instrument were made topheavy, so as to 

 give it a larger and larger eccentricity. Would the fact of the different 

 position of the centre of gravity make the difference? 



