Mr. W. Sturgeon on the Theory of Magnetic Electricity. 449 



With this magnetic force, and the assistance of a galvano- 

 meter which multiplied the electric force more than fifty times, 

 " a permanent deflection of the needle of nearly 4-5° could be 

 sustained." 



With my simple electrical machine, excited by a magnet of 

 about three pounds weight only, and a needle, supported on 

 a pivot, either above or below the edge of the revolving disc, 

 a permanent deflection of more than 40° can be exhibited. 

 And when two such magnets are employed, as in fig. 10, the 

 needle may be kept steadily deflected at right angles to the 

 plane of the disc. 



From this simple statement of facts, we readily perceive 

 that the apparatus of Mr. Faraday exhibits but a very small 

 portion indeed of the excited force in the disc, and leaves in 

 complete obscurity the finest application of that force ever ex- 

 hibited on the magnetic needle. 



The electric force which may be led or conducted by a wire 

 from a revolving disc may be very much exalted by taking 

 advantage of the distribution accomplished by the arrange- 

 ment of magnets exhibited in the following experiment. 



Experiment 23. — Let the disc revolve between the poles of 

 two horse-shoe magnets, having both the north poles on one 

 side, and consequently both the south poles on the other side 

 of the disc, as in fig. 11. (Plate I.) In this case the four sy- 

 stems of forces which flow over the surface of the disc give 

 two resultants in the same diameter. When the disc revolves 

 in the direction of the exterior arrow, those resultant forces 

 will run from between the poles of both magnets towards the 

 centre or axis of motion, where they meet. From the axis of 

 the disc, a portion of those forces may be led off by one or 

 more wires at pleasure. The resultant forces will be reversed 

 by reversing the direction of the revolving disc. 



When four or more magnets are similarly arranged on dia- 

 meters of the revolving disc, several resultants are driven to 

 or from the axis or centre. By this means the force led off is 

 very much increased. No application of magnets to revolving 



least 7 cwt. The power of this gigantic magnet on the iron rod is only 

 about one hundred pounds, or not quite fth of its own weight. This force, 

 however, must necessarily be much less than the magnet is capable of ex- 

 erting on a proper cross piece or lifter ; but it is not likely from this fact, 

 that it is capable of supporting its own weight. The horse-shoe magnet 

 which I described weighs between nine and ten pounds ; and its lifting 

 power equals one hundred and twenty pounds, or about twelve times its 

 own weight. 



Third Scries. Vol. 2. No. 12. Jwie 1833. 3 M 



