Results of Crystal Analysis. 65 



From (9), (10) we have 



m 2 q 2 = - -^N l7 /+^^-V a ~ y)i - 



- 1 - a — y \ ct-y) 



We have also 



;V = XeQs 1 q l '\' + n,q.^)-E ; 



so that a third relation is required in order that we should 

 kuow Nj, n 2 , and i. 



According to J. J. Thomson's theory, when there is only 

 one kind o£ ion in the tube, 



It is our intention to discuss the experimental results in 

 their bearing on this and other theories in a future paper. 



Our thanks are due to the authorities of the Presidency 

 College, Calcutta, for affording us facilities for carrying|on 

 the above investigations. 



VI. Results of Crystal Analysis. 

 By L. Regard, Dr.phil., University of Christiania *. 



[Plate III.] 

 § 1. TN a previous paper f I gave an account of the 

 JL crystalline structure of silver, as determined by 

 the Bragg reflexion method. The X-ray spectrometer was 

 in principle the same as that constructed by Bragg, only 

 differing with regard to details which were mentioned in 

 the paper. 



Since then the work has been continued, and some of the 

 results obtained will be given in this paper. 



Besides some results concerning the structure of gold 

 and lead, which were announced in a paper read before 

 " Kristiania Yidenskapselskap " on November 19, 1915, 

 the present paper will chiefly deal with the more elaborate 

 and complicated case, the determination of the structure 

 of the Zircon group, represented by the minerals zircon 

 (ZrSi0 4 ), r utile (Ti0 2 )2> and tinstone (kassiterite) (Sn0 2 ) 2 , 

 which are, as far as I know, the first cases of tetragonal 

 crystals which have yet been analysed J. 



Not being aware of the fact that the Spinel group recently 

 has been analysed by W. H. Bragg §, I have also made an 



* Communicated bv the Author, 

 t L. Vegard, Phil. Mag. Jan. 1916. 



X An account of the analysis of the Zircon group was given in a 

 lecture in Kristiania Vid. Selsk. March 10, 1916. 

 § W. H. Bragg, Phil. Mag. Aug. 1915, p. 305. 



Phil. Mag. S. 6. Vol. 32. No. 187. July 1916. F 



