3o8 



NATURE 



[June 20, 1918 



ship's clocks, and quoted in all time-readings. 

 Onlv one ambiguity would remain— that of the 

 Greenwich day. Uncertainty about this might 

 arise in the neighbourhood of the antimeridian of 

 Greenwich; the line of demarcation, which is 

 shown on the chart, is not quite regular, different 

 islands keeping Asiatic or American reckoning 

 according to their political affinities and history. 



It was with the view of lessening these difficul- 

 ties that Commandant Vincent added a day-hand 

 to his chronometer dial (see p. 146). . It is clear 

 that the difficulty is considerably increased by the 

 fact that at Greenwich two different systems, the 

 civil and the astronomical, are in use, the day be- 

 ginning at midnight and noon respectively. It is 

 hoped that the reform of using the former system 

 for all purposes may soon be introduced. From 

 the discussion that is now taking place, it is clear 

 that the only serious difficulty that is felt in the 

 matter is the breach that will be caused in the 

 continuity of astronomical records. This incon- 

 Acnience will be minimised if in all records, for 

 some years before and after the change, the time- 

 origin employed is clearly stated. 



Summer time is not to be used at sea ; it would 

 cause needless complication, and the reasons which 

 make it desirable on land are much less potent at 

 sea ; it will be remembered that navigation and 

 astronomy were excluded from the scope of the 

 Act, and the Greenwich ball has been dropped 

 throughout at i o'clock Greenwich time (2 o'clock 

 summer time). A. C. D. Crommelin. 



DAMASCENE STEEL. 

 iHiAIMASCENE or Damascus st^el made its 

 -L-' appearance in Western Europe during the 

 Middle Ages. It was manufactured in India, and 

 the origin of the process may be traced back 

 many centuries B.C. The same kind of steel had 

 previously been introduced into Russia, where it 

 was known as " poulad " or " bulat. " The ex- 

 ternal characteristic of this steel was its patterned 

 surface-watering or "jauher" (Persian), which 

 gave rise to the name "poulad jauherder. " It 

 was imported into Russia through Persia and the 

 Caucasus, and into Western Europe through 

 Syria and Palestine. 



A most interesting and important study of this 

 material was presented by Col. N. T. Belaiew 

 at the spring meeting of the Iron and Steel In- 

 stitute. According to his researches, there were 

 three principal methods of producing it : 



(i) The old Indian, by which crucible steel was 

 made by melting pure ore with the best kind of 

 charcoal; (2) the Persian, in which case pure 

 soft iron and graphite were the ingredients; and 

 (3) a particular heat treatment which was in the 

 nature of a prolonged tempering. 



The greatest care was taken in regard to the 

 temperature and duration of the melting process, 

 since it was known that the best "watering'' 

 could be obtained only with alloys which were 

 kept molten for a long time and afterwards 

 very gradually cooled. The fluid alloy was allowed 

 NO. 2538, VOL. lOl] 



to freeze in the crucible, and removed only when 

 cold in the form of a cake. 



These cakes have been described by Tavernier 

 and others, and were brought to this country by 

 Scott. Numerous investigations were carried out 

 on them, notably by Stodart and Faraday in 

 England, Reaumur and Breant in France, and 

 Anossoff in Russia. The last-named was led so 

 early as 1831 to apply the microscope to the study 

 of polished and etched surfaces, not merely of 

 these steels, but bIso of all his alloys that were in- 

 tended for industrial applications. He was the 

 first to classify the patterns of damascene blades, 

 and showed that in steels containing the least 

 carbon the watering took, the form of parallel 

 stripes, and that as the carbon increased these 

 became wavy, then mottled, and finally passed into 

 vertebrae, which were considered the most perfect 

 form. To this the Persians gave the name "kirk 

 narduban," or "forty steps of Mahomet's ladder." 



Col. Belaiew took up the experimental study 

 of these steels at the instigation of Prof. 

 TchernofT, who, in lecturing at the Michael Artil- 

 lery Academy, Petrograd, stated that " the best 

 kind of steel ever manufactured was undoubtedly 

 the bulat." He found that the majority of dama- 

 scene steels contained from i"i to i"8 per cent, of 

 carbon. The following is a complete analysis of 

 one of them : — 



c 

 1-49 



Mn Si S 



o-o8 o'oo5 005 



p 

 o"io 



He then proceeded to reproduce the steels 

 artificially at the Putiloff works, using the Eastern 

 Crucible method (soft iron and graphite), and 

 studied both the primary crystallisation (from the 

 melt) and the secondary (from the solid), and 

 showed that the latter differed in its form accord- 

 ing to whether the steels were hypo- or hyper- 

 eutectoid, i.e. < or > o'go per cent, of carbon. 

 Damascene steels all belong to the latter category. 

 He found that in all cases where the alloys were 

 slowly cooled a remarkably clear primary and 

 secondary crystallisation followed. The former 

 consisted of dendrites of austenite of very varying 

 carbon content, the latter of dendrites of cementite 

 which closely followed the orientation of the 

 austenite axes. The higher the carbon the 

 more closely did the primary and secondary 

 crystallisations resemble one another, and a 

 "structure of large crystals " resulted. To under- 

 stand how, from an alloy with this structure, the 

 beautiful wavy or motley watering of Oriental 

 blades can be obtained, he discusses the life- 

 history of a I '5 per cent, carbon steel from the 

 molten state. Every cake is either cut in two, in 

 which case each half makes the blade of a sabre, 

 or the central part is cut away and the remaining 

 ring is cut through at one place so as to facilitate 

 subsequent working and then drawn into a bar. 

 If the specimen is only drawn lengthwise the 

 "veins "produced are longitudinal and the water- 

 ing consists of parallel stripes or ronces. But if 

 the forging is executed in two or more directions, 

 then, " according to the skill of the workman and 



