150 



On Cohimbite. 



Fig. 1. 



1. Haddam, Conn. 2. Bodenmais, Bavaria. 3. Middletown, Conn. 



The specimens from the localities that afforded these two crystals 

 are correctly recognized by Dr. Thomson as belonging to the same 

 species. A simple inspection of figure 3, a representation of a Mid- 

 dletown specimen, seems to lead to the same conclusion respecting 

 its relation to the Bodenmais Columbite. This will be rendered more 

 apparent by comparing with the above the interfacial angles of this 

 crystal. These angles have been obtained by calculation ; they are 

 necessarily founded, however, on previous measurements, with which 

 they very closely agree.* 



a : a (over o') = 102° 58' 

 a : a (over e) = 117° 51' 

 a : a (over e) = 107° 56' 

 6' : 6' = 150° 17' 

 6" : 6"= 160° 29' 

 a : 6'= 156° 20i' 

 a : e=143° 58' 

 e : o"=170° 14^' 

 e : e=100° 40' and 79° 20' 

 In the calculations of these angles, the planes a, were assumed as 

 the faces of the fundamental form. We hence obtain for the val- 

 ues of the crystallographic axes, a = 1.0584 = V^1.12, 5=1.206 = 

 v^ 1.454, c=l ; and by inspection and calculation deduce the an- 



* The following values of these angles have been observed by C. U. Shepard. 

 (Shepard's Min. ii. 323.) 



P:a=127° ia:e=129°30' 



P : 6'=137° 20' ? M:e=112°10' 



P:e=160°23' o' ; o'=149° 30' 



M: e=157°40' a: 6 = 144" 



