4[4 Mr« Levy on the Origin of the 



little greater than a right angle *. I have determined the di- 

 mensions of this primitive form by means of the observed an- 

 gles P on g', P on (1, and P on e. Supposing besides that the 

 faces d and e are both the result of a decrement by two rows 

 in breadth, the one on the angle a and the other on the angle 

 a of the primitive ; I find then that the planes Mr. Phillips 

 has designated by ?«, ^S 5'^ Pj e, n, d, k, i, a, I, i\ h, which 

 are the only ones for which he has given measurements, may 

 be represented respectively by the following simple crystallo- 

 graphical signs, P,7«,g^, A', a^, o®, o'*,^', e^ ^^, b\bi,di. Their 

 calculated incidences are written below, and by the side of 

 them their differences with the observations. 



Diff. with Diff. with 



m, w = 115° 16' Observations. Observations. 



P, e^ = 128° 39' 30" . . 9' 30" 

 P, e^ = 147° 30' . - 10' 

 P, ^ = 157° 22' 40". . 2' 40" 

 m,b^ = 139° 45' ... 3' 

 m,bi= 157° 5' . . . 15' 

 7B, di = 157° 7' 30" . —22' 30" 

 h\dk= 141° 7' 30" — 12' 30<' 

 The above differences are so small that it may be inferred 

 at once that the crystals of Haytorite are perfectly regular, 

 and that one of the forms which may be taken as their primitive 

 can differ but very little from that above assumed; that is to say, 

 from an oblique rhombic prism the incidence of the lateral 

 planes of which is 1 15° 1 6', the incidence of the base on each of 

 them 90° 8' 30", and the lateral edge equal to the oblique dia- 

 gonal of the base. It is also obvious that if the primitive was 

 supposed to be a right rhombic prism, preserving still the 

 same incidence for the lateral planes, the differences between 

 the observations and the results of calculation would not be 

 much greater than above. But 1 think, however, that it is 

 better to consider the primitive as a slightly oblique rhombic 

 prism, because all the measurements of Mr. Phillips indicate 

 an inclination of the base in the same direction, and also be- 

 cause the symmetry of the crystals agrees better with it. 



When I first saw the drawings and measurements of Hay- 

 torite, I thought they might be considered as pseudomorphic 

 crystals of sphene, because some of the angles are not very 

 far from those of that substance. But the preceding investi- 

 gation proves, that an almost perfect equality must be esta- 

 blished between the angles of Haytoi-ite and those of any 

 other mineral, before it can be reasonably suspected that the 



* The drawings to be put in position with respect to this primitive form 

 should be inverted. 



crystals 



