40 



WRITINGS OF JAMES 8MITHSON. 



I have a very small, but very regular, crystal of the form 

 of Fig. 1. 



Fig. I 



Fig. 2. 



mp = 90 



m t =90 



a m = 135 



m b = 135 



c b = 125 15' 52" 



g b = 144 44' 8" 



d m = 116 33' 54" 



fm = 153 26' 6" 



By mensuration the faces a and m appear to form together 

 an angle of about 135, and the faces c and b an angle of 

 about 125. 



It is said in the account above quoted, that the primitive 

 form of this matter is a rectangular tetraedral prism, but 

 no proofs of this have been offered ; nor have the dimen- 

 sions of this prism been given, a circumstance of the first 



