372 Scientific Intelligence. 



gave opposite results in the cases of zinc and copper, placing them constant- 

 ly above and beloiv each other, according to the mode of observation employed. 

 Messrs Babbage and Herschel next investigated the effect of so- 

 lution of continuity on the various metals, and they ascertained the 

 curious fact, that the re-establishment of the metallic contact in other me- 

 tals, restores the force either wholly or in a great measure, even when 

 the metal used for soldering has in itself but a weak magnetic power. 

 Hence is obtained a power of magnifying weak degrees of magnetism. 

 They found also that the force varied inversely between the square and the 

 cube of the distance. 



From these valuable experiments, Messrs Babbage and Herschel con- 

 clude, that the phenomena may all be explained, by supposing time to be 

 requisite, both for the developement and the loss of magnetism, and that 

 different metals differ, in respect not only of the time they require, but of 

 the intensity of the force ultimately producible in them. See Quart. 

 Jour. vol. xxxviii. p. 276. 



14. On the Magnetism imparted to Iron bodies by Rotation. This is the 

 title of a paper read before the Royal,Society by Mr Barlow. Having fix- 

 ed a 13 inch mortar shell to the mandril of a powerful turning lathe 

 wrought by a steam-engine, and caused it to perform 64.0 revolutions in a 

 minute, the magnetic needle deviated several degrees from the magnetic 

 meridian, and remained stationary during the motion of the shell. When 

 the rotation ceased, it immediately resumed its original position. When 

 the motion of the shell was inverted, an equal but opposite deviation of the 

 needle took place. 



When the earth's action on the needle was neutralized, and the needle 

 made a tangent to the ball, the north end of the needle was attracted, 

 when the motion of the ball was made towards the needle, and repelled 

 when the motion was in the contrary direction, and this happened what- 

 ever was the direction of the axis of rotation. In the two extremities of 

 the axis, there was observed no effect, but in two opposite points, at right 

 angles to the axis, the effect was a maximum, and the deviation of the 

 needle was to the centre of the ball. In speculating on these facts, Mr Barlow 

 is disposed to think, that the earth's magnetism is of the induced kind, 

 and he considers this opinion as supported by the fact of the non-coin- 

 cidence of the magnetic axis with the axis of the earth's daily motion. 



15. Mr Christie's A r ew Experiments on the Magnetism produced by Ro- 

 tation. — In a letter to J. F. W. Herschel, Esq., which was read to the 

 Royal Society on the 16th June, Mr Christie has communicated the fol- 

 lowing facts : After confirming the results obtained by Mr Babbage and 

 Mr Herschel, as given above, Mr Christie found, that when a thick cop- 

 per plate is made to revolve under a small magnet, the force tending to make 

 the needle deviate 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 beneath copper discs, the force diminishes more nearly as 



