416 On the Conjugate Positions of two Circular Coils of Wire. 



combination, it may be observed that the greatest inductive 

 effect occurs when the planes of the coils are at the greatest 

 distance from one another — and that as the planes approach, 

 this effect gradually diminishes, until, when they still are at 

 some distance, it becomes nothing. 



Another, and perhaps more convenient, way of combining 

 them is to place them, as in the last case, with their planes 

 parallel and their axes coincident, the distance between them 

 being equal to, or a little greater than, the radius of either coil : 

 then, if their planes are vertical, we may fix one of them in that 

 position ; and if the other is capable of rotating round its ver- 

 tical diameter, it will be found that when it has rotated through 

 90° (that is, when the planes of the coils are at right angles) the 

 inductive effects in the secondary circuit have ceased. If the 

 coil is made to rotate through a few degrees to one side of this 

 position, the currents induced in it will be in a certain direc- 

 tion ; and if it is rotated to the other side, their direction will 

 be found to be reversed. 



As with either of these combinations we could pass from 

 sound to silence, some experiments were made in order to com- 

 pare the rate of diminution of the induced currents with the 

 movements of the coils in passing from a maximum to a mini- 

 mum of inductive effects. 



For this purpose the coils were placed with their faces in con- 

 tact and their axes coincident, the secondary one being joined 

 in circuit with a reflecting galvanometer. In this position 

 five observations were taken and the mean recorded. They 

 were now separated until their planes were an inch apart, and a 

 mean of five observations again taken ; and this process was 

 repeated at intervals of half an inch till the distance betw r een 

 them was increased to five inches. 



They were now arranged as in the first combination, their 

 faces being in contact during all the experiments ; and while 

 their axes were coincident, five observations were taken and 

 the mean recorded. One of them was now slid over the other, 

 the faces being still in contact, through a distance of half an 

 inch and a mean recorded as before ; and this process was re- 

 peated at intervals of half an inch till a balance was established. 



The second and third combinations were treated in the same 

 manner, the coils being moved by steps of 10° at a time, and 

 readings taken till a balance was obtained ; and as the deflec- 

 tions were small in all cases, they were taken as being propor- 

 tional to the strength of the currents. 



The numbers given in the annexed Table are those found 

 in the way indicated, the mean in each case being that of five 

 experiments. 



