OF AETS AND SCIENCES. 283 



From these we calculate 



XonY 104° 43' TouZ 71° 6' X on Z 71° 10' 



a:b:c = 0.7981 : 1 : 0.7207 



In addition to the above, selected as fundamental planes, we also 

 observed 



430; 054; 504? 740; 470; 474; 047? 



These symbols were for the most part deduced from the zone inter- 

 sections, and the indices could only in a few cases be verified by 

 angular measurements. The faces of the vertical prism especially 

 were very irregular, in consequence of the alternations caused by 

 parallel grouping, so common with artificial crystals ; and although 

 the relative position of the fundamental planes could be accurately 

 fixed, the symbols of the intermediate planes must be regarded as 

 doubtful ; these planes were seldom seen, and only in the vertical 

 zone. The symbols given on the projection were obtained by finding 

 the intersection with the vertical zone of other zones never well defined 

 on the same crystal, and it can only be claimed that the approximate 

 angular measurements on the vertical zone were compatible with the 

 indices given. The following additional angles were calculated and 

 verified by measurements when possible. 



