418 Miscellaneous Intelligence. 



towards the E ; and the intermediate positions had their motions 

 in intermediate directions. 



The tendency, therefore, of the wire to revolve in a circle 

 round the pole of the earth, is evident, and the direction of the 

 motion is precisely the same as that pointed out in the former 

 experiments. The experiment also points out the power which 

 causes Ampere's curve to traverse, and the way in which that 

 power is exerted. The well-known experiment, made by 

 M. Ampere, proves,' that a wire ring-, made to conduct a cur- 

 rent of electricity, if it be allowed to turn on a vertical axis, 

 moves into a plane east and west of the magnetic meridian ; if 

 on an E and W horizontal axis, it moves into a plane perpendi- 

 cular to the dipping-needle. Now if the curve be considered 

 as a polygon of an infinite number of sides, and each of these 

 sides be compared in succession to the straight wire just de- 

 scribed, it will be seen that the motions given to them by the 

 terrestrial pole, or poles, are such as would necessarily bring 

 the polygon they form into a plane perpendicular to the dip- 

 ping-needle ; so that the traversing of the ring may be reduced 

 to the simple rotation of the wire round a pole. It is true the 

 whole magnetism of the earth is concerned in producing the 

 effect, and not merely that portion which I have, for the 

 moment, supposed to respect the north pole of the earth as 

 its centre of action ; but the effect is the same, and produced 

 in the same manner ; and the introduction of the influence of the 

 southern hemisphere, only renders the result analogous to the 

 experiment at page 82, where two poles are concerned, instead 

 of that at page 77, &c., where one pole only is active. 



Besides the above proof of rotation round the terrestrial 

 pole, I have made an experiment still more striking. As in 

 the experiment of rotation round the pole of a magnet,, the pole 

 is perpendicular to but a small portion of the wire, and more 

 or less oblique to the rest, I considered it probable, that 

 a wire, very delicately hung, and connected, might be made 

 to rotate round the dip of the needle by the earth's mag- 

 netism alone ; the upper part being restrained to a point in 

 the line of the dip, the lower being made to move in a circle 

 surrounding it. This result was obtained in the following man- 

 ner : a piece of copper-wire, about 0.018 of an inch in diameter, 

 and six inches long, was well amalgamated all over, and hung by 

 a loop to another piece of the same wire, as described at page 

 285, so as to aliow very free motion, and its lower end was 

 thrust through a small piece of cork, to make it buoyant on 

 mercury; the upper piece was connected with a thick wire, 

 that went away to one pole of the voltaic apparatus ; a glass 

 basin, ten inches in diameter, was filled with pure clear mer- 

 cury, and a little dilute acid put on its surface as before ; the 

 thick wire was then hung over the centre of the glass basin, and 



