466 



NA rURE 



[March .19, 1908 



In 1849 Sorbv founded the science of petrography, 

 preparing in that 3ear the first rocli section ever 

 examined by transmitted light. His alleged " wild 

 ideas" as to the capabilities of this method were 

 laughed at by the authorities of the period. Indeed, 

 for a voung man, not long past his teens, to attempt 

 to upset the generally accepted dictum of de Saussure 

 that mountains could not be e.\amincd by micro- 

 scopes was regarded as bordering on presumption. 

 In the early 'fifties, Sorby was much engaged on the 

 subjects of the crystalline tetramorphism of carbon 

 and the vexed question of slaty cleavage. In con- 

 nection with the latter, in spite of rebukes, he per- 

 sisted in his work, and in 1857 the young man of science 

 buried both the electric and the 45° theories, by 

 proving that slaty cleavage was due to the fact that 

 lateral pressure on argillaceous rocks compressed 

 them in one direction, elongated them in another, 

 thus setting the small particles with their longest 

 dimensions parallel, and so developing the character- 

 istic structure in a plane perpendicular to the pres- 

 sure. 



In 1856 Sorby enunciated his now generally 

 accepted theory that the Cleveland ironstone hills 

 had been originally calcium carbonate, which had 

 been gradually replaced by carbonate of iron derived 

 from associated strata. 



In the organic world Sorby did much work on 

 colouring matters, and in this connection, for prac- 

 tical value, his microspectroscopic examinations of 

 blood perhaps stand first. In 1865 he described his 

 " new form of spectrum microscope " and the 

 results registered thereby before the British Associa- 

 tion. Proceeding upon information published bv 

 Hoppe, and two years later (1864) in greater detail 

 by Prof. .Stokes, Sorby exhaustivelv examined 

 the microspectroscopic properties of red and brown 

 cruorine and haematin, and from these figured no 

 less than seven characteristic absorption spectra, 

 showing incidentally that well-marked bands could 

 be obtained from a minute blood-stain when only one- 

 thousandth part of a grain of colouring matter was 

 present. The importance of such marvellouslv deli- 

 cate analysis was at once obvious to medical men 

 and public analysts liable to be called upon to give 

 evidence in criminal cases. 



.Sorby, the " Father of Petrography," was also 

 destined to become the Father of Metallography.' 

 His pioneer discoveries in petrography led him to 

 the sagacious conception that steel ftself might be a 

 crystallised igneous rock; and in February, 1864, he 

 placed in the hands of metallurgists for all time a 

 new and most valuable method of scientific investi- 

 gation. 



On that date he read before the Sheffield Literary 

 and Philosophical Society a paper " On a New 

 Method of Illustrating the Structure of Various 

 Kinds of Blister Steel by Nature Printing." In this 

 paper he revealed the cellular structure of hard blister 

 steel. He then attempted to produce artificial 

 meteorites, but his efforts were not attended with 

 success, because, as is known now, his experimental 

 conditions were unsuitable, and it was not until 1904 

 that an " artificial meteorite " was described in 

 Nature on November 10, p. 32. 



Sorby (as evidenced by the numerous carefully 

 dated and initialled iron and steel sections now in 

 the writer's possession -) worked on iron and steel 

 -netallography during the years 1863, 1864 and 1865, 



> The attempt made by an American writer' to transfer this title to a 

 Russian metallurgist is best answered by silence. 



_ - Some years ago the writer was exhibiting Sorbv's pioneer sections of 

 iron and steel at the Royal Institution, and was asked by an interested 

 sp ciator, How much each are you asking for them ? ■' 



NO. 2003, VOL. 77] 



and, taking into consideration the meagre chemical 

 data then extant, his final theory as to the nature 

 of steel seems almost of the order of inspiration. 

 He described crystals of nearly pure iron as consist- 

 ing probably of interfering cubes and octahedra, and 

 after a lapse of nearly forty-three years the accuracy 

 of his conclusions (with only sectional planes to guide 

 him) remains unshaken. In his " pearly constituent " 

 (now called pearlite) he discovered a mineral the 

 importance of which to mankind is still in this, the 

 steel age, imperfectly realised. His " intensely hard 

 constituent " is the cementite of the modern metallo- 

 grapher. The pearly constituent Sorby described 

 thus : — " The optical characters of this substance led 

 me to conclude that it had a very fine laminar 

 structure before I was able to prove it by the use 

 of high powers. It seems difficult, if not impos- 

 sible, to explain its structure by supposing that it is 

 an accidental mi.xture, whereas the facts are easily 

 explained, if we suppose that it e.xists as a compouini ' 

 at a high temperature, and breaks up into a mixture 

 on further cooling, as more fully described in my 

 paper on the use of high powers. For this reason 

 it will be convenient to retain the name pearly con- 

 stituent with the understanding that, as seen when 

 cold, it is a mixture." 



Persistent attempts to disprove the accuracy of 

 Sorby's views of the nature of pearlite have, up to 

 the present, consistently failed. Sorby's efforts to 

 analyse pearlite quantitatively by micrographic means 

 were, from the very nature of the problem, unsuc- 

 cessful. He provisionally suggested that the hard 

 plates constituted about 33 per cent, of the mass. 

 .Subsequent researches have shown that analyses on 

 planes of section are misleading. The quantitative 

 determination of the percentage and composition of 

 these plates in pearlite occupied (in the metallurgical 

 laboratories which were founded at Sheffield, largely 

 owing to the energy and interest of Dr. Sorby) :i 

 period of three years, 189 1-4, and was only accom- 

 plished by a triple attack conducted (a) by the micro- 

 ■scope ; (b) by quasi-quantitative pyrometric measure- 

 ments of the heat of transformation of pearlite ; and 

 (c") by differential chemical analysis of the carbides 

 as distinguished from carbon. The result obtained 

 and now generally accepted indicated that in pure 

 pearlite the percentage of hard plates always approxi- 

 mates 13. 



It would occupy an inordinate amount of space 

 even to summarise the results of Sorby's work ct>n- 

 ducted on his yacht Glimpse in connection with 

 marine zoology. Dr. Sorby was a member of the 

 Established Church, and made considerable researches 

 in ecclesiastical architecture. 



In concluding, it may be remarked that the final 

 answer to the more or less good-natured derision 

 with which his first rock section was regarded in 

 1849 was given, not by Dr. Sorby himself, but 

 fifty-seven years afterwards by a cloud of witnesses 

 at the centenary meeting of the Geological Societv 

 in February, 1906. Then many of the most distin- 

 guished foreign and British petrographers sent to the 

 invalid man of science the following special message, 

 expressing their " profound conviction of the important 

 service rendered to the branch of geological science 

 which they cultivate by the pioneer labours of Dr. 

 Henry Clifton Sorby. They deplore the circum- 

 stances which prevent him from joining them on 

 this interesting occasion, but beg to be allowed to 

 assure him of their great admiration of his life's 

 work, of their filial regard and deep affection." 



Of Dr. Sorby it cannot be said that a prophet 

 has no honour in his own country. Amongst the 



1 This is now known as fc.->rdenite (ivriter's note). 



