103 



June 15, 1854. (Continued.) 

 The EARL of ROSSE, President, in the Chair. 

 The following papers were read : 



Y. " The Attraction of Ellipsoids considered generally." 

 By MATHEW COLLINS, Esq., B.A. Communicated by 

 S. HUNTER CHRISTIE, Esq., M.A., Sec. R.S. &c. Received 

 April 27, 1854. 



The author commences by stating, that the attraction of an ellip- 

 soid on a point on its surface or within it, in a direction perpendi - 

 cular to one of its principal planes, is proportional to the distance of 

 the attracted point from that plane. 



This general proposition, which is an extension to ellipsoids of 

 those already given for spheroids in Airy's Tract " On the Figure of 

 the Earth," Prop. 8 and 10, and in MacLaurin's 4th Lemma, " De 

 causa physica Fluxus et Refluxus Maris," he demonstrates 



1 . In the case when the attracted point is on the surface of the 

 ellipsoid. 



The demonstration of this is much like those given by the above- 

 named authors for the less general case of spheroids, and its final 

 step is effected by Cor. 1 to Prop. 87 of the first book of the Prin- 

 cipia. 



2. When the attracted point is within the ellipsoid. 



The demonstration in this case is effected by showing that an 

 ellipsoidal shell, bounded by two similar and similarly placed ellip- 

 soidal surfaces, exerts no attraction on a point situated anywhere 

 within it or upon its interior surface. 



The foregoing proposition shows that the attraction of an ellip- 

 soid on any point on its surface, or within it, can be got at once from 

 the attraction of the same ellipsoid on a point placed at the extre- 



VOL. VII. M 



