38. The Rev. R. Murphy's Remark on an Error 



examined for potash, traces of which were readily found. 

 According to the total result, the green particles consist of 



[M. Berthier's analysis of the green 

 particles from near Havre gave 

 the following proportions: — 



Silica 50-0 



Protoxide of iron ... 21*0 

 Alumina 7'0 



Silica 48-5 



Black oxide of iron 22*0 



Alumina 17*0 



Magnesia 3*8 



Water 7*0 



Potash traces 



98-3 



Water 110 



Potash 10-0 



99-0.] 



It is superfluous to speculate on the precise atomic con- 

 stitution of the green particles, since they were not obtained 

 in a state of perfect purity. The ingredients which appear to 

 be essential, both from the quantity in which they occur, and 

 their constancy in the colouring matter of green-sand from 

 different localities, are silica, alumina, oxide of iron, magnesia, 

 and water. I should hence consider the green matter as a 

 hydrated silicate of alumina, magnesia, and black oxide of 

 iron, and as being, in all probability, the true green earth, or 

 earthy chlorite of mineralogists. The analyses of chlorite 

 hitherto published are so discordant as to prove, either that 

 different compounds have been examined under the same 

 name, or that the specimens under examination were very im- 

 pure. The essential ingredients, however, appear to have 

 been the same as in the subject of my analysis. 



Though the foregoing description applies more immediately 

 to the colouring matter of the green-sand from the vicinity of 

 Folkstone, I have obtained similar results on examining that 

 from Hythe and several other places. Indeed, from the ex- 

 amination of many samples of green-sand collected by Dr. 

 Fitton from various localities in England and France, I be- 

 lieve the colouring matter to be precisely the same in all. 



VII. Remarks on an Error of M. Fourier in his Analyse des 

 Equations. By the Rev, R. Murphy, M.A. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



T^HE first part of M. Fourier's posthumous work on the 



-*■ analysis of determinate equations was published in 1831, 



the editor being M. Navier, of the Academy of Sciences of the 



