448 Mr. Levy on Murchisonite. 



fected in only one way. Now the most important part of my 

 paper is occupied in endeavouring to show that the proof 

 offered by Laplace is insufficient, and in giving a demonstra- 

 tion not liable to the same objections. Laplace's proof pro- 

 fesses to be general ; mine applies only to the cases in which 

 y can be expressed (at any rate approximately) by a rational 

 function of the coordinates. Where then is the unavoidable 

 consequence of which Mr. Ivory speaks ? I have endeavoured 

 to show that the fundamental equation of Laplace is general, 

 but that its application to the theory of the attractions of solids, 

 is restricted by the limited nature of the proof of one of the 

 subsequent steps. In this I can discover no inconsistency, 

 nor do I perceive that I have embroiled the subject with new 

 difficulties. I have only done with regard to one point, what 

 Mr. Ivory has done respecting another : I have endeavoured 

 to show that a demonstration professing to be general, is un- 

 satisfactory, and have substituted one which appears, though 

 more restricted, to be better founded. 



I am sorry that I should have come in contact with Mr. 

 Ivory, for the first time, on an occasion so disagreeable. I am 

 not desirous of appearing in a public controversy of this na- 

 ture; and under any common censure I should have remained 

 quiet. But the manner in which I have been mentioned is so 

 gross, and the name of the person who has mentioned me 

 stands so high, that I have no other resource than to lay my 

 defence before all who have read the accusation. I am aware, 

 that the Editors of a Philosophical Journal can take little plea- 

 sure in inserting the squabbles of quarrelsome writers; and 

 therefore, whatever further provocation maybe offered, I shall 

 not trouble you again with my complaints. 



I am, Gentlemen, yours, &c. 

 Trinity College, Cambridge, May 9, 1827. G. B. AlRY. 



LXXXVII. Oil a neio Mineral Substance, proposed to be called 

 MuTchisonite. By A. Levy, Esq. M.J. F.G.S. 



IN looking over some specimens of the conglomerate of the 

 new red sandstone, which Mr. Murchison had brought 

 from the neighbourhood of Dawlish, and which he was so 

 good as to show me, 1 observed, in many of them, a felspar- 

 like laminated substance, with a peculiar nacreous cleavage, 

 which induced me to believe, it might differ from common 

 felspar. Upon further examination I found that it had cleav- 

 ages 



