W. E. Ford — RemarTcable Twins of Atacamite. 19 



Faces 



of , 

 No. II 



m' 



Measured 



Calculated 



45'* 1 



38 I 



25 I 



20 J- 



31 I 



3 

 12 



47= 



47 



45 



46 



46 



46 



46 



80° 48'* 

 80° 9' 



J 



Average 



46° 31' 



80° 29' 



83° 



84 



83 



82 



85 



84 



84 



48° 

 47° 



56'^ 



8 

 46 

 58 



2 

 54 



2 



35' 



Average 



> 83° 49' 47° H' 84° 31' 



47° 51' 81° 9' 48° 17 



2. Angles measured on a one-circle goniometer between 

 faces of individuals I and II. 



Measured Average Calciilated 



106° 24' 



105 54 



106 23 

 106 3 



■e' of No. I ,s e' of No. II 



m of No. I ^ e' of No. II 



m'" of No. I/vm" of No. II 



m of No. I /\ m" of No. II 



5' 

 6 

 5 

 5 



10 = 



11 



10 



11 



67° 

 68 



44' 

 20 

 54 

 36 



39' 

 17 

 42 

 17 



1 



)- 106° 11' 106° 10' 



I 



J 



I 



I 



\ 

 J 



] 



j. 11° 1' 



I 

 J 



5° 53' 



10° 57' 



!*' i 67° 58' 67° 54' 



\ 



m"' of No. I /s m' of No. II 76° 56 1 



76 

 76 

 76 



6 

 59 

 50 



)■ 76° 42' 76° 29' 



i 



The above tables give all the measured angles on the differ- 

 ent crystals without regard to the quality of the faces and the 

 consequent authority of the angles. In general, however, the 

 average values of the angles of the different series are reason- 

 ably close to the calculated angles. In the case of the table of 

 the measurements made on the two-circle goniometer the 

 angle, derived from the measurement of the best crystal and 

 the one which permitted of the most accurate adjustment on 

 the goniometer, is given first in each list and is further marked 

 by an asterisk. The agreement between these angles and the 

 corresponding theoretical values is quite close. The widest 

 variation between the measured and the calculated angles is to 

 be found in the case of the faces in the prism zone, and with 



