June 24, 1922] 



NATURE 



817 



institutions be formed in other countries, the Astro- 

 nomical Society (rejecting all views but that of 

 benefiting science) would be ready and desirous to 

 divide at once the labour and the glory of this Hercu- 

 lean attempt, and to act in concert together in such 

 manner as should be judged most conducive to the 

 end in view. 



It is largely the Herculean nature of the task before 

 us which has led to astronomy being to-day (whether 

 for good or ill) the most highly organised of the sciences. 



The accomplishment of these objects has not been 

 rapid. A passage in the First Annual Report of the 

 Council mentions as one of the greatest desiderata 

 a means of determining the apparent magnitudes of 

 the stars^ and ascertaining " a correct scale whereby 

 astronomers may be enabled to express themselves 

 in one common language on this subject." The 

 lapse of a century has not quite sufficed for the 

 completion of this uniform scale ; but the main diffi- 

 culties have been surmounted, and the time is very 



near now when all astronomers will be able to express 

 themselves in a common language in regard to stellar 

 magnitudes, both visual and photographic. 



The foundation of our Society on January 12, 1820, 

 caused a ripple in the aether which has spread out ever 

 since in widening circles. To-day that ripple embraces 

 about 5000 of the fixed stars. The remaining thousand 

 million or so are still outside. Though a good many 

 of the best-known stars must by this time have received 

 the tidings, 90 per cent, of the naked-eye stars are 

 still in ignorance. We should like to think that the 

 stars of the morning sing together with joy on this our 

 Centenary ; but the cold truth must be faced that not 

 I in 100,000 can yet have heard of our birth. But we 

 shall look out on the heavens again to-night with re- 

 newed enthusiasm and joy ; and if from the majority 

 of the stars we can expect no more than an unrecognis- 

 ing stare, there are half-a-dozen old favourites which — 

 we may fairly be persuaded — will give us an answering 

 twinkle. 



X-Ray Studies on the Crystal Structure of Iron and Steel. 



AT the annual meeting of the Iron and Steel 

 Institute last year. Dr. Westgren presented a 

 paper on some X-ray crystallographic investigations 

 on iron and steel. At that time the photograms on 

 which his conclusions regarding the crystal structure 

 of the steel components were based were not very 

 clear, and were not published. More- 

 over, owing to spontaneous crystal 

 growth at high temperatures, the 

 photogram of gamma iron at 1000° C. 

 did not show any continuous lines, 

 but only a few spots. Since then. 

 Dr. Westgren has continued his 

 investigations and improved the ex- 

 perimental arrangements, and in a 

 paper published with Mr. Phragmen 

 at the corresponding meeting of the 

 Institute on May 5 last, he showed 

 photograms of very great interest and 

 significance. 



The X-rays were produced in a tube 

 of the Seigbahn type. Difficulties had 

 previously been experienced in obtain- 

 ing vacuum-tight bronze tubes which 

 composed the metal body. A more 

 suitable material has been found in Skefko ball- 

 bearing steel, which is remarkably free from slag 

 inclusions and heterogeneities. The anti-cathode 

 was cut off perpendicularly to its axis, and in 

 order to get the characteristic X-rays of iron, 

 which are very convenient for these investigations, an 

 iron plate was soldered on to it. Round the radiating 

 surface five windows were made. The tube therefore 

 gave five beams, and exposures could be made in five 

 cameras simultaneously. The tube was evacuated by 

 the combination of a mercury vapour jet pump and a 

 mercury diffusion pump of the Volmer type. Special 

 arrangements were made for maintaining the vacuum 

 of the desired quality. The tube was usually charged 

 with 45,000-50,000 volts and run with 10-12 milli- 

 amperes. 



NO. 2747, VOL. 109] 



In investigating the crystal structure of pure iron 

 at different temperatures, a wire (0*3 millimetre 

 diameter) of vacuum-melted electrolytic iron contain- 

 ing 99-98 per cent, of the metal was investigated. 

 Arrangements were made for rotating this three or 

 four times per minute during exposures. Photograms 



were taken at the ordinary temperatures, and at about 

 800°, 1100° and 1425° C, which gave information of 

 the structures of the iron in the alpha, beta, gamma and 

 delta ranges (Fig. i). The time of exposure was 2 J hours. 

 The lines in the photograms obtained at the ordinary 

 temperatures are clear and sharp, but in the higher 

 ranges of temperature investigated they appear broad 

 and not very distinct. The author explains this as due 

 to the fact that the iron wire at temperatures of about 

 1400° C. is extremely pliable. Its position, therefore, 

 changed somewhat during the exposure. Moreover, 

 he found it very difficult to keep the temperature of 

 the wire steady in the delta iron range. If the tempera- 

 ture was maintained at 1450° C, i.e. within about 70° 

 of the melting point, the wire became so soft that it 

 could not stand the torsion. The temperature, there- 



