Dr Turner's Analysis of Mica from Cornwall. 137 



dip, will not only account for the phenomena in general, but 

 that the deviations deduced from such a supposition will very 

 nearly correspond with those actually observed. 



Some singular circumstances attend the effects which Mr 

 Christie has described as arising from rotation : these effects 

 appear to be nearly independent of the velocity of rotation ; a 

 single revolution of the plate, or even less, is sufficient to pro- 

 duce the whole effect ; and the effect is permanent, so long as 

 the plate remains perfectly stationary after having revolved. 



Since making these experiments, Mr Christie has, we under- 

 stand, tried the effect of rapid rotation, and has found, that 

 the deviations of the needle during the rapid rotation of an 

 iron plate, are in the same direction as those which take place 

 after the rotation, whether slow or rapid, has ceased, the plate 

 revolving in the same direction in the two cases ; but the ex- 

 tent of deviation during rapid rotation is greater than that 

 after rotation, which appears to be permanent, nearly in the 

 ratio of three to two. It appears, therefore, that the same 

 polarising of the iron will account for the deviations in the 

 two cases, but that during rapid rotation the intensity of the 

 poles is increased. 



As the magnetic phenomena, arising from the rotation of 

 different bodies at present excite a considerable degree of in- 

 terest, we have no doubt that this brief sketch of those which 

 Mr Christie first observed more than four years ago, (and we 

 are not aware that such had ever been observed, or even hint- 

 ed at before,) will be acceptable to our readers. 



Art. XXVIII. — Analysis of a Mica from Cornwall. By Ed- 

 ward Turner, M. D. F. It. S. E. &c. Lecturer on Che- 

 mistry, and Fellow of the Royal College of Physicians, 

 Edinburgh. Communicated by the Author. 



Having accidentally in my possession some of the rose-co- 

 loured mica from Chursdorf in Saxony, in which Professor 

 Gmelin has detected the presence of lithia,* and being struck 

 with the characteristic appearance it exhibits when heated by 



• See his Analysis in the last Numher of this Journal. 



