January 22, 1920] 



NATURE 



545 



SYMPOSIUM ON THE MICROSCOPE. 



THE s)'mposium and general discussion on the 

 microscope, held on January 14 by the Faraday 

 Society, the Royal Microscopical Society, the Optical 

 Society, and the Photomicrographic Society, in con- 

 junction with the Optical Committee of the British 

 Science Guild, attracted a very large audience, which 

 the meeting-room of the Royal Society proved quite 

 inadequate to accommodate. The objects of the sym- 

 posium, as stated by Sir Robert Hadfield in his intro- 

 ductory address, were : — 



(a) Improvement in the technique of the microscope 

 itself, including its manufacture. 



(b) Improvement in lenses, including eyepieces and 

 objectives of high power. 



(c) Improved application of. the microscope for re- 

 search in ferrous and non-ferrous metallurgy. 



With such extensive ground to be covered it is not 

 surprising that the programme of papers presented 

 was much longer than could possibly be read during 

 the meeting. Many of these were of great interest, 

 and, as the majority were in type before the meeting, 

 the aims of the symposium might perhaps have been 

 more fully achieved had these been taken as read and 

 the time thus saved utilised for discussion. It will 

 onlv be possible in the space available for this article to 

 record a few of the more salient points brought for- 

 ward at the meeting. 



Sir Robert Hadfield, who was in the chair, opened 

 the afternoon session by giving a brief history of the 

 microscope and its applications in metallurgy down 

 to the present day. In addition, he contributed papers 

 on the Faraday Society and on the work of Sorby, 

 a bibliography of the chief literature relating to the 

 microscope, and a series of photomicrographs of steel 

 and iron sections at magnifications ranging from 9 up 

 to 8000 diameters. He was followed by the presidents 

 of the various participating societies, by microscope 

 manufacturers, and by other prominent workers, who 

 each dealt with some special aspect of microscopy. 

 Prof. Cheshire indicated the importance of microscope 

 production as a measure of the standing of the optical 

 industry of any country. Other speakers touched on 

 ground which was to a considerable extent traversed 

 by many other contributors. On one subject, at any 

 rate, all the speakers were agreed — the necessity for 

 proper training in the use of the microscope, whether 

 for visual or photographic use. This will be clearly 

 realised by those who note how frequently those with 

 extensive experience in microscopical research refer to 

 the importance of securing proper conditions of 

 illumination. The absence of proper courses in this 

 subject was compared by Sir Herbert Jackson with the 

 very thorough courses now available in spectroscopy. 

 That instruction is needed in our universities in the 

 use of the microscope and in the interpretation of the 

 effect seen — nay, more, in the proper appreciation of 

 optical theory itself — was proved beyond any doubt 

 to the meeting. 



Compared with the unanimity on the need for 

 education, there were very marked divergences in the 

 views expressed by nearly all the speakers on detailed 

 matters. Consider, for instance, the desirability of 

 obtaining increa.sed magnification with greater resolv- 

 ing power. Many of the most experienced metal- 

 lurgists who expressed their views anticipated that anv 

 considerable increase in resolving power would be 

 likely to afford clues to .some of those problems which 

 to-day are most baffling in the production of metals 

 with specific properties. It is suggested, for instance, 

 that with improvements in the resolving power the 

 mysterious alterations in the mechanical properties of 

 metals brought about by cold working would be ex- 

 plained. The papers abound with examples of the 

 NO. 2621, VOL. 104] 



valuable information that has been derived from past 

 increases of aperture ; nevertheless, some workers are 

 satisfied that further advantage in this direction is not 

 to be expected, and it is even suggested that the N.A. 

 of objectives has already been increased too greatly. 



The same extent of disagreement was shown in 

 discussing the relative merits of British and German 

 stands and lenses. For some purposes, at any rate, 

 very experienced workers give decided preference to 

 the English stand, though this is said to be less con- 

 venient for metallurgical work. No stand now made, 

 it was said, is sufficiently rigid to enable the micro- 

 scope to be changed from the vertical to the horizontal 

 position without disturbing the relative adjustment of 

 the specimen and the optical system. Modern de- 

 signers were recommended to study Powell's model of 

 1841 as an admirable example of what is required. 

 One important criticism was to the effect that the 

 materials employed by the British makers were too 

 soft, particularly for such working parts as the racks 

 and pinions, with the result that after a few years 

 all the movements were too loose. In this respect 

 German instruments had been found more satisfactory 

 bv some workers, though this was not the experience 

 of all. 



As regards objectives, it was not denied that the 

 best home-made products were fully as good as those 

 made abroad, but it was contended that this standard 

 of excellence was reached in a smaller proportion of 

 the objectives produced than in the foreign lenses. 

 The importance of a highly trained test-room staff was 

 emphasised in this connection. It may be noted as a 

 point of interest, mentioned by Mr. F. Twyman, that 

 good objectives have been found to show differences of 

 phase in the emergent wave-front of about one wave- 

 length. 



During the meeting it was announced that one or 

 two makers would shortly place upon the market new 

 designs of objectives made from English glasses. It 

 is satisfactory to learn that the different varieties of 

 glass required for these objectives have been produced 

 in this country. To determine how these glasses com- 

 pare with the German lenses of Zeiss, a committee of 

 expert microscopists was appointed to investigate and 

 issue a report. In view of what was said regarding 

 the general standard reached, it would be as well, if 

 this proposal were carried a step further, and it 

 became customary for manufacturers to issue with 

 their objectives a certificate issued, say, by the 

 National Physical Laboratory. If the required 

 standard for a certificate were maintained at a 

 reasonable level, with due regard to periodical im- 

 provements, such a system should go far to remove 

 the impression that it is necessary to go to Germany 

 for a thoroughly good objective. 



There are many other points to which attention 

 might be directed, but for these reference must be 

 made to the printed papers. The apparent lack of 

 enterprise on the part of the manufacturer since the 

 war has, however, been fully explained. He has been 

 busy for the first time in making arrangements for 

 the mass production of microscopes by modern 

 machine methods. This is of the first importance, 

 for in the past few years nearly all the microscopes 

 required for biological work — and this covers possibly 

 as much as go per cent, of all microscopes made — ■ 

 have been imported. The hand-made English instru- 

 ment could not possibly compete either in price or in 

 quality with the machine-made article. Should it be 

 possible to regain a large share of this trade while 

 retaining the best features of the more expensive and 

 elaborate models, the future position of the industry 

 in this country will be assured. It is to be hoped 

 that this development will not , be hindered, as was 

 suggested, by lack of capital. 



