420 



Prof. E. Edlund on the Theory 



Fig. 6. 



are not of equal magnitude. They are in any case so small 

 that it would be impossible for them to produce an appreci- 

 able current, even if they acted in the same direction. 



2. In experiment No. 4 of § 2, the jacket and the metallic 

 wire were in rotation with "the same angular velocity. As 

 it would be impossible to use a galvanometer to measure the 

 current, recourse was had to chemical tests to show the exist- 

 ence of a current. It is easy to deduce the results of formula 

 (6) mentioned above, drawn from the 

 mechanical theory of heat. Let sn 

 (fig. 6) represent a vertical magnet, of 

 which the poles are situated at s and n, 

 and let a b be a concentric jacket en- 

 circling the magnet, and put in contact 

 at the points a and b with the metallic 

 wire a lie gb. We will suppose now 

 that the jacket a b and the wire ahegb 

 are put into rotation round the axis of 

 the magnet, so that each part of the 

 circuit formed moves with the same 

 angular velocity v. The lines s e and 

 s h denote two planes passing through 

 the magnetic pole, and through the 

 direction of motion of the two points e 

 and h. We will suppose the angle 

 fse between the two planes to be very 

 small. If the distance from s to e is 

 denoted by the velocity of the point, e 



would be denoted by pvr x where p is a constant. The length 

 of the normal ef drawn to the plane s h is equal to r x sin ( fse) . 

 The element of the circuit eh ( = As of formula 6) multiplied 

 by cos [fell) ( = cos yjr of formula 6) is equal to ef=i\$m{fse). 

 If the closed circuit seen from above is in rotation in a direction 

 opposite to that of the hands of a watch, and if s is the south 

 pole, there is produced in e h an electromotive force tending 

 to produce a current in the direction of the arrow. Sine 

 of formula (6) is equal to unity, since the direction of motion 

 makes a right angle with the line joining the element to the 

 pole. If we denote by M the intensity of the magnetic pole, 



M 



and consequently by - 2 the intensity of the magnetic field at 



the point e, we shall obtain from formula (6), for the induction 

 in the element of circuit e h, the expression 



