500 



soniewhat uncertain, and that furtlier the correction for thickness 

 of preparation brings with it a relatively large nncertainty for these 

 lines. 



Fig. 1. 



From llie given values of .4 and q, there follows for the edges of 

 the elementary-cell: ^ = 5,84.10'^ and r = 0,406 ^/ = 2,37. 10" » cm. 

 in tig. 1 a representation of an elemenlary-cell is given. 



In the space-netting, built of these cells, we see alternating 

 equidistant hiyei's with distance 1, 19.10"^ cm. The tirat layer has a 

 netting of squares with side 5,84.10^ cm., the next 'a netting of 

 squares with side 4.13.10 ^ cm., which last S(|uares ai-e just above 

 the squares symmetrically inscribed in that of the tirst layer. 



The dense crowding of these planes indicates a strong force- 

 exertion in a direction, perpendicular . to the layers; perhaps the 

 occurrence of needle shaped combinations is connected with this fact. 



Röntgenometrical investigations teach us to cast a look in the 

 structure of the crystal and may for that reason lead us to a more 

 rational choice for the system of crystal lographic axes than the 

 former crystallographic methods. The white tin procures an example 

 of this. So e.g. the bipyramid, accepted by Miller as (111) (proportion 

 of axes a: (I : c^\ : 1 : 0,3857) would, conform to the system of 

 axes formed from the edges of the elementary cell proposed by us, 

 be indicated as (403); just so the planes (110), (100), (101) of Miller 

 by (100), (110), (223) resp. according to us. 



