184 R. W. G. Wyckoff — Determination of the 



Hemihedral Photographs : 



T 2 , T h 3 , and T h 4 : No classes of all odd planes are 

 absent in the first order. Second order reflections are 

 absent from T h 4 for planes of the forms {Ohl} and {hOl}, 

 where h is even and I is odd. 



Holohedral Photographs : 



T d 2 , O 3 , 0% O h 5 , and O h 7 : No classes of all odd 

 planes are absent in odd orders. From O 4 only fourth, 

 eighth, etc., orders from planes of the form {100} are 

 present. Second order reflections from O h 7 are absent 

 for planes of the form {Old} where k is even and I is odd; 



T d 5 , O h 6 , and O h 8 : Planes with all odd indices are 

 present in odd orders except those of the form {KM}, 

 where h = ± k. Second order reflections from O h 8 of 

 planes of the form {Ohl}, where k is even and I odd, are 

 absent. 



Space Groups based npon a Body Centered Cubic 

 Lattice, in general planes having two odd and one even 

 indices appearing in odd orders : 



Hemihedral Photographs: 



T 3 , T 5 , and T h 5 : No classes of two odd and one 

 even planes are absent ; 



T h 7 : Planes of the form {Okl}, where k and I are 

 both odd, are absent from odd orders. 



Holohedal Photographs : 



T d 3 , O 5 , O 8 and O h ° : No classes of two odd and one even 

 planes are absent in the first order. Reflections in the 

 second order from planes of the form {100} are absent 

 for O 8 . 



T d G : Planes of the forms {Ml} where \h is even and I 

 odd are absent in odd orders. In the second order, planes 

 of the forms {hhl}, where either h is even and I odd, or 

 both h and I are odd, are absent. 



O h 10 : Planes of the form {Okl}, where k and I are odd, 

 and of the form {Ml}, where \h is even and I is odd, are 

 absent in the first order. Reflections in the second order 

 are absent for planes of the forms {hhl} where either 

 h is even and I odd or both h and I are odd. 



