Royal Society. 30'S 



mena that he encountered, was a very great diminution of magne- 

 tic force, when a ring of the same weight was substituted for a disc ; 

 and pursuing this point of inquiry, he found, that in all cases of so- 

 lution of continuity, not only by cuts in the direction of radii from 

 the centre, but also in concentric annuli or otherwise, there is al- 

 ways a great loss of force ; the magnetism of the whole being always 

 much greater than the sums of that of the parts. 



In reasoning on the experiments detailed, Mr. Christie concludes 

 that the greater development of magnetism in a disc subjected to 

 the action of revolving magnets, takes place, when the axes of the 

 magnets are vertically under points bisecting the radii, and that the 

 magnetism decreases very rapidly as they approach the edge; thus 

 indicating that for a full development of magnetism, a continuity 

 of substance in all directions from the point acted on is principally 

 requisite. Various phaenomena lead also to the conclusion that the 

 reduction of the disc by concentric and radiating cuts into very 

 small portions, would render its magnetism quite insensible. 



The author next proceeds to investigate by experiments of the 

 same kind, the law of variation of the magnetic force, regarded as 

 depending on the distance of the revolving magnets from the sus- 

 pended body. Assuming in this investigation, as a consequence of 

 the principles proposed by other writers, that the action may be 

 referred to a single point or pole in the copper ring, somewhat in 

 arrear of the point vertically over the magnet, and also that the 

 mutual action of tiiis pole, and the single point near the extremity 

 of each magnet to which its action may also be referred, is inversely 

 as the 4-th power of their distance, he found these laws to be esta- 

 blished by the experiments, made in various ways. 



Lastly, Mr. Christie enters into an analytical examination, the 

 object of which is to ascertain how far the principle of time being 

 required for the development of magnetism, will account for the 

 phaenomena; and the conclusion at wliich he arrives, is, that it will 

 do so satisfactorily. In the course of this examination, he infers 

 that in certain cases a retrograde rotation in the suspended disc 

 might take place, and suggests the great confirmation which such 

 a fact, if observed, would afford this theory. 



A notice was read, entitled, " Correction of an error in a paper 

 published in the Philosophical Transactions, entitled ' On the paral- 

 lax of the fixed stars;' by J.F. VV. Herschel, Esq.,IVI.A. Sec. K.S."; 

 and a paper was also read, entitled, " On attractions apparently 

 magnetic exhibited during chemical combination ; by W. L. Hen- 

 wood, Esq." : communicated by Davies Gilbert, Esq. M.P. V.P.R.S. 



March 1. — Dr. J. C. Prichard was admitted a Fellow of the So- 

 ciety ; and a paper was read, entitled " On the structure and use 

 of the submaxillary odoriferous gland of the Crocodile ; by Thomas 

 Bell, Esq I'.L.S. ": communicated by Sir E. Home, Bart., V.P.R.S. 



Beneath the lower jaw of the Alligator and the Crocodile, on each 

 side, is situated a gland which secretes an unctuous substance of a 

 strong musky odour. About two years since, the author of this 

 paper discovered in it a structure which is without parallel in the 

 glandular system of other animals. His observations were made on 

 the common American Alligator. In this animal the external ori- 

 fice 



