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On the Magnetism developed in Copper and other Substances during 

 Rotation. In a Letter from Samuel Hunter Christie, Esq. M.A. 

 S(C. to J. F. W. Herschel, Esq. Sec. R.S. Communicated by J. F. 

 W. Herschel, Esq. Read June 16, 1825. [Phil. Trans. 1825, 

 p. 497.] 



Mr. Christie in this communication gives an account of some ex- 

 periments on the development of magnetism in copper by rotation. 

 He corroborates by his own experience the results obtained by Mr. 

 Babbage and Mr. Herschel, in which a disc of copper was set in ro- 

 tation by the rotation of one or more magnets beneath it, both in the 

 case when poles of the same name were immediately below the disc 

 and when of a contrary name. The action appeared equally intense 

 in both cases, and from this circumstance the author concludes the 

 magnetism thus communicated to the copper to be extremely trans- 

 ient. The experiment was varied by combining the revolving mag- 

 nets differently, and the results are stated. 



The next experiments of Mr. Christie were directed to the deter- 

 mination of the law according to which the force diminishes as the 

 distance between the disc and magnets increases. It seems to follow 

 from these experiments, that when a thick copper plate is made to 

 revolve under a small magnet, the force tending to deviate the needle 

 is directly as the velocity, and inversely as the fourth power of the 

 distance ; but that when magnets of considerable size are made to 

 revolve under these copper discs, the diminution follows more nearly 

 the ratio of the inverse square of the distance, or between the 

 square of the cube, though not in any constant ratio of an exact 

 power. 



The author then investigates the law of force when copper discs 

 of different weights are set in rotation, which for small distances ap- 

 pear proportioned to the weights of the discs, but for greater ones 

 appear to vary in some higher ratio. 



On the annual Variations of some of the principal Fixed Stars. By 

 J. Pond, F.R.S. Astron. Royal. Read June 16, 1825. [Phil 

 Trans. 1825, p. 510.] 



This communication consists of a table stating the annual varia- 

 tions of 23 of the principal fixed stars, as deduced from Dr. Brink- 

 ley's observations, and those of the Astronomer Royal. On these 

 Mr. Pond remarks, that out of 16 stars observed at Dublin, 13 either 

 indicate a southern deviation, or at least are not inconsistent with it, 

 and that of these 13, about half indicate a greater deviation than that 

 assigned by Mr. Pond himself. The other half a less, while the 

 three remaining stars deviate northwards. 



Mr. Pond further remarks, that the examination of this table is 

 calculated rather to increase than to diminish scepticism on the sub- 

 ject of the determination of such very small quantities by astronomi- 

 cal observations. He concludes by disclaiming all intention of placing 



