250 Mr. William Phillips on the 



than that assigned to it by Haiiy. However it must be allowed 

 that, on taking into consideration the circumstances that all the 

 brilliant crystals did not agree in yielding the same results, and of 

 my being compelled for want of brilliant fractures, to depend on 

 the natural planes, it is possible that the measurements on which 

 I rely may not be absolutely correct. 



Like most other hard and brittle substances, the hyacinth most 

 readily yields to the pincers. 



Staurotlde. 



Fig. 2. 



In regard to this substance also I rely on the measurements ob- 

 tained by means of the reflecting goniometer on the natural planes. 

 The form of the primimitive crystal is a right rhomboidal prism 

 (fig. 2) of which the admeasurement of M on M is given by Haiiy 

 as l'z9° 30'. Two of the only three crystals that were submitted 

 to that instrument agree in affording, each two measurements of 

 that angle 129° 20', and each also two of M on the adjacent plane 

 over the edge A 50° 40'. The other affords one of 129° 20' ; only 

 two of its planes give clear reflections ; which on the faces of the 

 other two crystals were remarkably clean and well defined. These 

 crystals are from St. Gothard. 



Anatase. 



Fig. 4. 



The form of the primitive crystal of anatase is an elongated octo- 

 hedron of which the common base is square. Of nine isolated 

 crystals in my possession only two are sufficiently brilliant for the 



