314 ROTATION BY ELECTRICITY. SECT. XXX. 



Mercury has been made to rotate by means of Voltaic electricity, 

 and Professor Ritchie exhibited in the Royal Institution the sin- 

 gular spectacle of the rotation of water by the same means, while 

 the vessel containing it remained stationary. The water was in 

 a hollow double cylinder of glass, and, on being made the con- 

 ductor of electricity, was observed to revolve in a regular vortex, 

 changing its direction as the poles of the battery were alternately 

 reversed. Professor Ritchie found that all the different con- 

 ductors hitherto tried by him, such as water, charcoal, &c., give 

 the same electro- magnetic results when transmitting the same 

 quantity of electricity, and that they deflect the magnetic needle 

 in an equal degree when their respective axes of conduction are 

 at the same distance from it. But one of the most extraordinary 

 effects of this force is exhibited by coiling a copper wire, so as 

 to form a helix or corkscrew, and connecting the extremities of 

 the wire with the poles of a galvanic battery. If a magnetized 

 steel bar or needle be placed within the screw, so as to rest upon 

 the lower part, the instant a current of electricity is sent through 

 the wire of the helix, the steel bar starts up by the influence of 

 this invisible power, and remains suspended in the air in opposi- 

 tion to the force of gravitation (N. 224). The effect of the 

 electro-magnetic power exerted by each turn of the wire is to 

 urge the north pole of the magnet in one direction, and the south 

 pole in the other. The force thus exerted is multiplied in degree 

 and increased in extent by each repetition of the turns of the 

 wire, and in consequence of these opposing forces the bar re- 

 mains suspended. This helix has all the properties of a magnet 

 while the electrical current is flowing through it, and may be 

 substituted for one in almost every experiment. It acts as if it 

 had a north pole at one extremity and a south pole at the other, 

 and is attracted and repelled by the poles of a magnet exactly as 

 if it were one itself. All these results depend upon the course of 

 the electricity ; that is, on the direction of the turns of the screw, 

 according as it is from right to left, or from left to right, being 

 contrary in the two cases. 



The action of Voltaic electricity on a magnet is not only pre- 

 cisely the same with the action of two magnets on one another, 

 but its influence in producing temporary magnetism in iron and 

 steel is also the same with magnetic induction. The term in- 

 duction, when applied to electric currents, expresses the power 



