Mr Voysey on the Diamond Mines of Southern India. 97 



1825, a copy of my paper " on the effects of temperature on 

 the intensity of Magnetic Forces, and on the Diurnal Varia- 

 tion of the Terrestrial Magnetic Intensity? read before the 

 Royal Society in June 1824, I thought it would be proper 

 to call your attention to a note, in which I had mentioned the 

 discovery I had some years before made, respecting the effects 

 due to the rotation of iron, at the same time to give a brief 

 notice (little more than the note itself,) of the principal of 

 these effects, and likewise to state, that the same supposition 

 of the iron being polarised in a direction perpendicular to the 

 dip, would account both for the phenomena observed after 

 rotation, and likewise those during its continuance. This was 

 the only notice of these experiments which I sent to any Jour- 

 nal. I must therefore leave the responsibility of the " very 

 injudicious remark" complained of, with whoever may have 

 made it ; at the same time stating, that I am not aware of the 

 remark alluded to. Others must decide to whom the implied 

 \f want of candour"' 1 should be appropriated. 



Having so frequently witnessed the application of Mr Bar- 

 low's correcting plate, I am, of course, perfectly aware, that 

 all motion of rotation is prevented, when the plate is once per- 

 manently placed in its position ; but should circumstances re- 

 quire its removal and replacement, its magnetism would, in 

 particular situations, be materially affected by any rotatory 

 motion given to it, when applied on the axis, although every 

 point might be brought into precisely the same situation which 

 it had previously. I am therefore still of opinion, that it 

 would be advantageous, if the axis were so formed, that this 

 motion of rotation, on applying the plate, should be pre- 

 vented. I remain, Dear Sir, yours very truly, 



S. H. Christie. 

 Royal Military Academy, 



4>th November 1826. » 



Art. XII. — On the Diamond Mines of Southern India. By 

 H. W. Voysey, Esq.* 



Having lately visited some of the principal diamond mines of 

 Southern India, the few facts I have been able to collect re- 



* Abridged from the Asiatic Researches, vol. xv. p. 120. 

 VOL. VI. NO. I. JAN. 1827. G 



