CONTEMPORARY ADVANCES IN PHYSICS 



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We will now work out the details of the diffraction-pattern of a 

 cubic lattice. This kind of lattice is much the easiest to treat, and 

 Nature has kindly bestowed it on many of the commonest crystals. 



90 120 150 ISO 210 240 

 AZIMUTH ANGLE — DEGREES 



270 300 330 360 



P^ig. 13— Diffraction-peaks obtained with a fixed crystal and monochromatic elec- 

 tron waves (the two curves correspond to different wave-lengths chosen because they 

 satisfy the condition for producing diffraction-beams) by moving a collector around 

 so as to capture one beam after another. (Davisson and Germer.) 



In the cubic lattice, the nearest neighbors of any atom-group lie at 

 equal distances from it along three directions at right angles to one 

 another. Moreover any atom-group in the entire (perfect) lattice 



