307 



also be referred to a single point or pole in the copper ring, some- 

 what in arrear of the point vertically over the magnet, as a conse- 

 quence of the principles proposed by other writers on the same sub- 

 ject ; and, lastly, that the mutual action of these poles on each other 

 is inversely as the 4th power of their distance. Assuming then a 

 formula with indeterminate co-efficients expressive of these condi- 

 tions, and determining them by comparison of the assumed with the 

 observed forces, he finds that the effect of a variation of distance 

 from \ an inch to 2^ (which causes a diminution of force from 

 1982*5 to 11-375, the ratio of nearly 200 to 1,) can be represented 

 within a 40th of the whole force, in the extreme case where the ob- 

 servations are liable to the greatest errors, and in all other cases to 

 the 100th part of the force ; so that he considers this law as esta- 

 blished by experiment. The same operations give the values of the 

 assumed constants ; and it may be remarked that these agree very 

 nearly as deduced from different experiments, and that as a mean 

 result, we may state the distances of its pole from the extremity of 

 each magnet, at 105 thousandths of an inch ; and the distances by 

 which the pole of the disc is in arrear of that of the magnet, with 

 the velocity employed, at about four tenths of an inch; and the intro- 

 duction of this element gives a considerable increase of coincidence 

 between observed and computed results. 



The author next proceeds to apply similar processes of assump- 

 tion and calculation to the case where the magnets were made to 

 revolve horizontally under the ring, with their poles of the same name 

 adjacent. In this case his observations also lead to the conclusion 

 of a law of force, varying inversely as the 4th power, instead of the 

 inverse square of the distance, between the poles of the magnets 

 and the corresponding poles in the ring. 



He now reversed the experiments, suspending the magnets over the 

 ring in a vertical position, and making the ring revolve below them 

 till the magnets had attained a state of equilibrium, between the force 

 of the disc in one direction, and that of torsion and their own di- 

 rective force in the opposite. The same result is still obtained from 

 this experiment, viz. a variation of the force as the inverse 4th 

 power of the distance. 



Mr. Christie next enters into an analytical investigation, having for 

 its object to ascertain how far the principle of time being required 

 for the developement of magnetism will account for the phenomena ; 

 and the conclusion to which he arrives is, that it will do so satisfac- 

 torily. In the course of these investigations, he is led to conclude 

 that, in certain cases, a retrograde rotation in the suspended disc 

 might take place ; and suggests the great confirmation such a fact, 

 if observed, would afford to this theory. 



