January 22, 1920] 



NATURE 



537 



course, at low magnifications, leave little to be 

 desired in regard to sharpness and beauty. A 

 collection of Sorby's original polished and etched 

 sections of metals is carefully preserved by the 

 University of Sheffield, and was lent on the occa- 

 sion of the symposium. 



Sorby's discovery aroused little interest, and 

 when, in 1877, Prof. Martens, of Berlin, soon fol- 

 lowed by Osmond and by Le Chatelier in Paris, 

 began the study of metals with the aid of the 

 microscope, the work of their predecessor had 

 been forgotten. By this time, however, a general 

 interest in the subject had been awakened, and 

 Sorby's important papers in the Journal of the 

 Iron and Steel Institute in 1886 and 1887 met 

 with a more appreciative audience. By employing 

 higher magnifications, Sorby was able to show that 

 the "pearly constituent" of steel, as he had called 

 one of its principal constituents, owing to the 

 mother-of-pearl lustre often exhibited by it, was 

 in reality an aggregate of parallel plates of a soft 

 and a hard material. This discovery placed the 

 metallographv of steel on a firm basis, and pre- 

 pared the way for the complete explanation of its 

 structure when thermal methods were added to 

 those of the microscope. Great as were the 

 services of other investigators, it is to Sorby that 

 we owe, without question, our modern metallo- 

 graphic methods. 



Sorby laid great stress on the extension of our 

 knowledge by the use of higher magnifying 

 powers, so well illustrated by his own discovery 

 of the true nature of pearlite. Most metallographic 

 work is done at magnifications not exceeding 500 

 diameters, but excellent results have been obtained 

 by some workers with magnifications of 1000 and 

 even of 1500 diameters. The minuteness of many 

 metallic structures, especially those of hardened and 

 tempered steels, has made many metallographers 

 wish for a means of applying much higher mag- 

 nifications. Since the discovery of new detail 

 depends, not on the magnifying power, but on the 

 resolving power of the microscope, it is necessary 

 to increase the latter. This may be efTected either by 

 increasing the numerical aperture of the objective, 

 or by shortening the wave-length of the light used 

 for illumination. The numerical aperture can be 

 increased beyond its present maximum only by the 

 use of other materials than glass, a plan which is 

 likely to be adopted at some future time, whilst 

 the use of ultra-violet light, the magnificent results 

 of which in bacteriology were shown at the meet- 

 ing by Mr. J. E. Barnard, has so far given disap- 

 pointing results with metals. 



A valuable contribution to the study of highly 

 magnified metal sections was made by the third 

 paper under notice, that by Sir Robert Hadfield 

 and Mr. T. G. Elliot. The numerous and very 

 beautiful plates illustrate both the advantages of 

 high magnifications and the pitfalls which have to 

 be avoided if success is to be obtained. For ex- 

 ample, a field containing ferrite and pearlite is 

 shown in three photographs, all taken at a mag- 

 nification of 600 diameters, but with objectives of 

 different resolving power. With a 12-mm. objec- 



NO. 2621, VOL. 104] 



A 



tive, the pearlite is structureless (Fig. i), and only 

 when a 2-mm. apochromat is used is its minute 

 lamination fully revealed (Fig. 2). Another pearl- 

 ite has its structure revealed at 1500 diam. 

 (Fig. 4), but becomes much clearer at 5000 

 (P'gf- 5)> using the same objective. No further 

 advantage is shown at 8000 diam. The effect of 

 narrowing the aperture too much is shown by the 

 apparent broadening of the cementite lamellae in 

 the pearlite, the true breadth being seen very 

 clearly when the iris diaphragm is opened suffi- 

 ciently. The photographs, all of which are re- 

 markably good, may be said to be most successful 

 in the case of pearlitic structures. The structure 

 of martensite at 5000 diam. is not so clearly seen 

 as at a much lower magnification, whilst the 

 minutely granular structures of troostite and 

 sorbite evidently call for a higher resolving power 

 rather than for mere enlargement to indicate their 

 true nature. The paper will serve a most useful 

 purpose in directing attention to the nature of the 

 problem, and perhaps attracting skilled optical 

 workers and physicists to its solution. 



C. H. D. 



REPORT OF THE CALCUTTA 

 UNIVERSITY COMMISSIONA 



T first sight a report in five volumes, each 

 of upwards of four hundred pages, on the 

 Calcutta University Commission would appear 

 somewhat portentous ; but anyone alive to the 

 importance of university education in India who 

 makes a study of these volumes will be quickly 

 reconciled to their length and number. For it 

 may be fairly claimed that they contaih scarcely 

 a sentence which one would desire to see omitted. 

 The whole report of the Commission, including 

 evidence and appendices, comprises no fewer than 

 thirteen volumes, but we are here concerned only 

 with the first five. Vols, i., ii., and iii. contain a 

 very masterly analysis of the present conditions of 

 education obtaining in Bengal, and vols. iv. and v. 

 the actual recommendations of the Commission. 



Although this report ostensibly deals only with 

 education in Bengal, the greater part of it natu- 

 rally has bearing on our educational systems 

 throughout India. The whole report is a model 

 of style, and bears testimony to the infinite pains 

 and care taken by its editors. The names of the 

 members of the Commission were a sufficient 

 guarantee of its thoroughness and accuracy. The 

 review of the present conditions of education in 

 Bengal constitutes in itself one of the most valu- 

 able documents for the student of British rule In 

 India. Reports, annual and quinquennial, have 

 been issued in quantity from the various secre- 

 tariats in India, but we know of nothing to com- 

 pare for thoroughness and instructiveness with the 

 chapters under review. 



It is, of course, impossible for U3 in this place 

 to do more than refer briefly to one o.- two of 



1 Reports of the Calcutta University Commission, 1917-19. (Calcutta 

 Superinten'lent Government Printine. InHia, 1919.) Prices: Vol. i., Parti. 

 31. ; Vol. ii., Part i., v 6rf. : Vol. iii,, Part i., is. 6rf. ; Vol. iv., Part ii., 

 2s f>d. ; Vol. v., Part li., 2*. 



