382 Mr. T. S. Hunt on the Mineral Wilsonite. 



the fourth approximation, which would require an amount of 

 calculation that I am not prepared to undertake. I must con- 

 tent myself with having thrown out these suggestions. 



If the equation CA 2 =yu, 2 he true, it follows as a consequence 

 that the equations (C), (C), (C"), &c. contain the disturbing 

 force as a factor. In my first researches I endeavoured to show 

 antecedently that this is the case. But on reviewing the reason- 

 ing on this point, given in the Philosophical Magazine for August 

 1854, and in the Supplementary December Number (p. 524), I 

 find that the inconsistencies in the approximations to the mean 

 distance and mean motion of the apse there spoken of, disappear 

 when due regard is paid to the order of magnitudes proper to 

 each approximation, and in consequence that the argument 

 founded on the occurrence of those inconsistencies is invalid. 

 This point is fully cleared up in the present communication. 



Cambridge Observatory, 

 April 16, 1855. 



LIV. Note on the Mineral Wilsonite. 

 By T. S. Hunt, of the Geological Commission of Canada*. 



IN the Supplementary Number of this Magazine for July 

 1854, p. 499, I published descriptions and analyses of two 

 minerals occurring in crystalline limestone in Bathurst, C.W., 

 one of which I proposed as a new species with the name of Wil- 

 sonite. It was described as forming rose-red, translucent, clea- 

 vable masses, probably monoclinic in crystallization, with a hard- 

 ness of 3-5, and a density of 2'765 to 2 - 776. Lustre vitreous, 

 shining occasionally, pearly on the cleavage surfaces. One of 

 three analyses gave silica, 43'55 ; alumina, 27"94; oxides of iron 

 and manganese, *20 ; lime, 6'50 ; magnesia, 3"81 ; potash, 8*37 ; 

 soda, '95; water (loss by ignition), 8 , 61 = 99 , 93. "With two 

 other specimens the amounts of silica, alumina, magnesia, and 

 alkalies were very nearly the same, while the loss by ignition 

 was 9'40 and 9*00, and the amounts of lime respectively 6'94 

 and G-72. 



The subsequent examination of more perfect specimens in the 

 possession of Prof. E. J. Chapman has shown him that this 

 mineral is triclinic, with inclination to the right, and he has 

 kindly furnished the following notes : — " I give you as approxi- 

 mations, the following angles from cleavage faces by the common 

 goniometer :— P : T = 94° j P : e= 145° ; T : e = 129° ; P : M and 

 T:M = 110° to 115°. Cleavage with P and T perfect, less so 

 with M ; the cleavage with e is not easily obtained, but is very 



* Communicated by the Author. 



