164 Prof. A. Ogg on the Crystalline 



(110) planes, but the relative intensities of the spectra from 

 the (111) planes do not agree. The}' find the ratio of the 

 intensities of the first and second order spectra 60 : 100, 

 while I found 30 : 100. 



The relative intensities of the spectra from this plane are 

 of importance since the ratios of the spacings are deduced 

 from them. It was therefore thought advisable to repeat 

 these measurements 4 using wave-length 0/581 x 10 -8 cm. 

 The experiments which have been made confirm the ratio 

 30 : 100. 



The Arrangement and Spacing of the Planes. 



(a) (111) planes. 



James and Tun stall * conclude from the ratio of the 

 observed intensities 60 : 100 : 48 : : 15 that the planes 

 belonging to one of the lattices divide the distance between 

 those belonging to the other in the ratio of 0'389 : 0*611, 

 there being a phase difference of 110°. 



The ratios of the observed intensities, putting the second 

 order equal to 100, have been found to be 30 : 100 : 33 : 4 : 12. 



From these we conclude that the two sets have a phase 

 difference of 148°, and that the planes belonging to one set 

 divide the distance between those belonging to the other 

 set in the ratio 0*412 : 0*588. 



If we assume a normal set t of spectra to be in the 

 ratio 100 : 34 : 14 : 7 : 4, we find the calculated ratios are 

 30 : 100 : 31 : 5 : 15, which is in good agreement with the 

 observed ratios 30 : 100 : 33 : 4 : 12. 



{b) (110) planes. 



The planes occur in pairs with equal number of atoms in 

 each plane. The spacing is in the ratio 0*117 : 0*883. The 

 intensities of the first three orders should be 100 : 21 : 3. 

 The observed ratios were J 00 : 17 : 0. James and Tunstall 

 found 100 : 20 : 0. 



(c) (100) planes. 



The intensities were found to correspond nearly to those 

 of a normal set of spectra. The planes occur in pairs of 

 small phase difference, the ratio of the spacings being 

 0*058 : 0-942. 



* James and Tunstall, he. cit. 

 f James and Tunstall, he. cit. 



