Scr. XXXf. DEFLECTION OP THE NEEDLE. 315 



positions of the conducting wire, and every direction of 

 the Voltaic current, together with all the other phe- 

 nomena 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 hith- 

 erto 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 ex- 

 erted by an electrical current upon either pole of a 

 magnetic has no tendency to cause the pole to approach 

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

 tricity be supposed to pass through the center of a circle 

 whose plane is perpendicular to the current, the di- 

 rection 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). Consequently 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 two-thirds of a small mag- 

 net were immersed in mercury, the lower end being 

 fastened by a thread to the bottom of the vessel con- 

 taining the mercury. When the magnet was thus floating 

 almost vertically with its north pole above the surface, a 

 current of positive electricity was made to descend per- 

 pendicularly through a wire touching the mercury, and 

 immediately the magnet began to rotate from left to 

 right about the wire. The force being uniform, the 

 rotation was accelerated till the tangential force was 

 balanced by the resistance of the mercury, when it be- 



