July 8, 1922] 



NA TURE 



47 



found to be due to a submarine earthquake which 

 broke up many miles of the ocean floor. The occur- 

 rence may be compared with a similar commotion 

 which destroyed an important fishery in the sub-tropical 

 waters of the United States. 



A full and comprehensive appreciation of sub-tropical 

 ichthyology is necessary to indicate the vast and 

 interesting variety of the fauna and the intrinsic charm 



of scientific research. It is the duty and interest of 

 the community to discover the potential genius and 

 place him where he can accomplish that for which he 

 is fitted, unfettered by the suppressing restrictions of 

 a false communistic socialism or cramping of individual 

 effort. 



.Magna opera Domini exquisitae omnes 

 voluntates ejus. 



Ten Years of X-ray Crystal Analysis. 



By Dr. A. E. H. Tutton, F.R.S. 



A SPECIAL number of Die Naturwissenschaften, 

 t\ entitled " Zehn Jahre Laue-Diagramm," was 

 issued on April 21, forming Heft 16, 1922, which con- 

 tains eight articles by authors who have contributed 

 to the subject of X-ray analysis on the continent since 

 its first inception by Dr. M. von Laue, among whom 

 may be mentioned Drs. Friedrich and Knipping, who 

 collaborated with Dr. von Laue in the first discovery, 

 Prof. Debye, and Prof. Niggli. Probably the article 

 of deepest interest to the general reader will prove to 

 be that of Dr. Friedrich, who gives an account of the 

 circumstances in the year 1912 in Munich when the 

 first discovery was made. To the present writer, 

 who was himself in Munich in the summer of that 

 same remarkable year, this memoir is of fascinating 

 interest. It has to be remembered that the scientific 

 coterie at that time forming the professorial staff of 

 the University, Museum, and Institute, included Prof. 

 Rontgen, the generally recognised discoverer of X-rays 

 (although their production had for some time previously 

 been almost a daily occurrence in the private laboratory 

 of the late Sir William Crookes) ; Prof, von Groth, 

 the founder and editor of the Zeitschrijt fur Kry ^allo- 

 graph ic and the doyen of crystallographers, whose 

 brilliant lectures on crystal structure and optics 

 attracted students from all over the world ; Prof. 

 Sommerfeld, who had carried on the tradition of X-ray 

 physics bequeathed to him by his predecessor Boltz- 

 mann. and also extended the work of Haga and Wind, 

 and of Walther and Pohl on X-radiograms and the 

 general physics of X-rays ; Prof. Ewald, who had 

 studied the behaviour of long electromagnetic waves 

 w ith space-lattices ; and Dr. von Laue, who had 

 specialised largely on the interference phenomena of 

 ordinary optics. It was among this strong combina- 

 tion of crystallographers. X-ray specialists, and dif- 

 fraction (grating) opticians that the inception of the 

 attack on crystals by X-rays had its birth. 



During a conversation between Laue and Ewald, 

 the former raised the question as to how electromagnetic 

 waves would behave which were small compared with 

 the grating constants, and from his optical experience, 

 he suggested that diffraction spectra should be pro- 

 duced. The order of the space-lattice cell dimensions 

 of crystals was already known to be about an Angstrom 

 unit (10 " 8 cm.), from the density and molecular weight 

 of the crystal and the mass of a hydrogen atom. Tin- 

 work of Sommerfeld and of Walther and Pohl had led 

 us to expect that the order of dimensions of the wave- 

 length of X-rays would be about one-tenth of this 

 (io~ s cm.). Consequently Laue suggested that the 

 conditions should be particularly favourable for the 



NO. 2749, VOL. I io] 



origination of interference phenomena on the passage 

 of X-rays through crystals. 



The discussion was continued in the common room, 

 and taken up by the whole, deeply interested coterie, 

 and Friedrich, who was at the time acting as Sommer- 

 feld's assistant, declared himself, with youthful en- 

 thusiasm, ready to test the idea practically. He 

 secured the assistance of Knipping, who had more 

 spare time at his disposal, and together they set up 

 the now famous arrangement of X-ray bulb, leaden 

 screens with slits for ensuring the exit of a definite 

 beam of X-rays, simple goniometer carrying the 

 crystal, and photographic plates to receive the ex- 

 pected radiations. At the first attempt the sensitive 

 plates were only arranged parallel to the primary beam 

 of X-rays, as any effect expected appeared likely to 

 be of the character of secondary rays from the crystal, 

 and it was only on repeating the exposure with a 

 photographic plate arranged behind the crystal, per- 

 pendicular to the direct beam, that the first Laue 

 radiogram with a crystal of zinc blende was obtained, 

 after several hours of exposure. 



Friedrich describes how excited and delighted he 

 was when, alone in his working room at the Institute 

 late that night, he saw the spots appear on the plate 

 under the influence of the developer, due to the de- 

 flected X-rays, now known to be reflected from the 

 planes of atoms within the crystal, the planes of the 

 atomic space-lattice. Next morning he went early 

 to show the negative to Knipping, and together they 

 hastened to Laue and Sommerfeld, who were both 

 naturally equally interested and delighted. Prof. 

 Sommerfeld at once excused his assistant from his 

 ordinary duties, so that he might go ahead with further 

 experiments. Both Profs, von Groth and Rontgen, 

 to whom the result of the experiment was at once 

 communicated, supplied materials and gave valuable 

 advice. A much better and more accurate apparatus 

 was erected, including a good goniometer for the exact 

 adjustment of the crystal (which is particularly neces- 

 sary), and the excellent X-radiograms of zinc blende, 

 quartz, rock-salt, and other crystallised substances, 

 now so well known were obtained as the immediate 

 results. 



Dr. Knipping directs special attention in his article 

 to the remarkable work of Siegbahn, who worked with 

 an evacuated apparatus, so as to exclude air absorption 

 of the X-rays, and measured the wave-lengths of the 

 " softer " long wave-length portion of the radiation, 

 eventually discovering and measuring rays as long as 

 ten Angstrom units. Compton, it will be remembered, 

 at the "other extreme, has measured X-rays (y-rays 



