356 ROTATION BY ELECTRICITY. [SECT. xxxr. 



north towards the east or west, according to the direction 

 in which the current is flowing ; and, on reversing the 

 direction of the current, the motion of the needle will be 

 reversed also. The numerous experiments that have been 

 made on the magnetic and electric fluids, as well as those 

 on the various relative motions of a magnetic needle under 

 the influence of galvanic electricity, arising from all pos- 

 sible positions of the conducting wire, and every direction 

 of the Voltaic current, together with all the other pheno- 

 mena of electro-magnetism, are explained by Dr. Roget in 

 some excellent articles on these subjects in the Library of 

 Useful Knowledge. 



All the experiments tend to prove that the force emanating 

 from the electric current, which produces such effects on the 

 magnetic needle, acts at right angles to the current, and is 

 therefore unlike any force hitherto known. The action of 

 all the forces in nature is directed in straight lines, as far as 

 we know ; for the curves described by the heavenly bodies 

 result from the composition of two forces; whereas that 

 which is exerted by an electrical current, upon either pole 

 of a magnet, has no tendency to cause the pole to approach 

 or recede, but to rotate about it. If the stream of electricity 

 be supposed to pass through the centre of a circle whose 

 plane is perpendicular to the current, the direction of the 

 force exerted by the electricity will always be in the tangent 

 to the circle, or at right angles to its radius (N. 217). Con- 

 sequently, the tangential force of the electricity has a 

 tendency to make the pole of a magnet move in a circle 

 round the wire of the battery. Mr. Barlow has proved that 

 the action of each particle of the electric fluid in the wire, 

 on each particle of the magnetic fluid in the needle, varies 

 inversely as the squares of the distances. 



Rotatory motion was suggested by Dr. Wollaston. Dr. 

 Faraday was the first who actually succeeded in making the 

 pole of a magnet rotate about a vertical conducting wire. In 

 order to limit the action of the electricity to one pole, about 



