288 Prof. A. Des Cloiseaux on the three Types of Hum tie. 

 Tabic (continued). 



Scacchi's 



symbols. 



Symbols of 

 Des Cl. 



1 



Miller's 

 symbols. 



Calculated 

 angles. 



Observed 

 angles. 

 Scacchi. 



A:n 2 



pa 3 



00 1:2 1 1 



103 12 



103 12 



C:m 2 



ff 1 ^ 



10:211 



135 40 



135 41 



C : « 2 ' 



9 X W 



010:2 10 



*135 41 



135 41 



A.r 



P V 



00 1:112 



135 20 



135 18 



A:r' 



pd% 



001:223 



135 19 



136 (nearly )DesCl. 



3 



b 1 and c£* holohedral in Humite (v. 

 chondrodite (Des CL). 



Rath) and in 





pb$ 001:223 125 52 





A:r 2 



pd\ 1 001:1 111 125 50 i 



125 52 



V* and d* holohedral in Humite ( 



v. Rath). 



A:r 3 



pb\ 100 1:111! 113 28 



113 28 





pb* 00l:22l! 113 25 



113 10 (nearly) D. 



b* and ^ 

 drod 



r holohedral in Humite (v. Rt 



ite (Des CL). 



ith) and in chon- 



A:r* j jtm {001:1 1 Oj 98 12 



98 18 



a 2 =u=(b 1 b*h 1 ), /3 = (bn*h l ), V = (b 1 b?h*) = az = (b 1 b?h 1 )=:p, 

 of which a part = A 3 , are shown in fig. 228 of my ' Manual.' 



The plane of the optic axes is inclined from behind forward 

 (from a 1 towards o*), and makes an angle of about 30° with 

 the base. In chondrodite the twins are of a more or less com- 

 plex character, and consist of laminae twinned parallel to the 

 base, which extinguish the light well. The laminae are asso- 

 ciated along undulating surfaces, which cannot be referred to 

 either of the two planes adopted by Scacchi. 



The accompanying figure shows one of the crystals observed 

 by me. 



The number and extent of the 

 twin laminae are different in each 

 specimen : but all obey the same law 

 of association. 



The acute bisectrix is positive 

 and normal to the plane of sym- 

 metry. 



2H a .,= 86°27 / . 

 2H„, 6 =8G° 38'; /><*>, weak. 



