PKOCEEDINGS OF THE .SOCIETY. 91 



believe that the lecture they had just heard was not merely interesting, 

 but epoch-making. Mr. Barnard had dealt with two subjects, the one 

 the practical application of skiagraph methods to microscopic objects, 

 the other the possible future development of microscopy on other lines, 

 by the aid of X-rays. The Chairman referred to the great importance 

 of the first method of which they had had such beautiful illustrations, 

 but what in the speaker's mind constituted the epoch-making nature of 

 the lecture, was the idea, for the first time publicly recorded by 

 Mr. Barnard this evening, that X-rays might be made available in the 

 service of microscopy for increasing resolving power now that they were 

 proved to be akin to light waves, but of infinitely shorter wave-length. 



For thirty years or more there had seemed to be no possible means 

 of increasing the power of resolution of the Microscope to any marked 

 degree. Mr. Barnard had that evening indicated what the speaker felt 

 sure would be the future lines of progress and development. He had 

 felt that conviction from the moment that it had been suggested to him 

 by Mr. Barnard in a conversation they had had early last year, not long 

 after the publication of Friedrich, Knipping, and Laue's famous paper, 

 in which the properties of X-rays were first shown to resemble those of 

 light rays in ways which had not till then been demonstrated. 



At the present time its application to microscopy was still only 

 theory, and it might very well take a long time before substantial pro- 

 gress could be made, and the technique of the methods to be employed 

 worked out, but he thought Mr. Barnard's communication would scarcely 

 fail to have the important effect of stimulating research in this direction. 



It w r as desirable to free one's mind from the idea that the future 

 Microscope, utilizing X-rays, would be anything like the present form 

 of instrument. When it came to dealing with wave-lengths, a thousand 

 or even a few hundred times shorter than those of ordinary light, it was 

 manifestly impossible to use anything in the nature of lenses. That 

 would be like trying to skate on a road paved with cobble-stones. 

 Lenses had to be polished so that any irregularities of their surfaces 

 bore a small proportion to the wave-lengths of the light they were used 

 with ; it was hopeless to expect any approach to that with artificially 

 polished lenses, when wave-lengths of the order indicated came into 

 question. It was probable, therefore, that, in the first place, all would 

 have to be done by means of instruments with reflecting surfaces. It 

 was that which had led Mr. Barnard to make experiments with curved 

 mica plates, to see whether it was possible to expand and contract the 

 cones of X-rays, for the power of contracting and expanding cones of 

 light was the primary essential to any optical method of magnification. 



Mr. Rheinberg then reverted to Mr. Barnard's improved method of 

 producing skiagrams of microscopic objects, remarking on the ingenuity 

 of the arrangements used. Regarding the possible limits of magnifica- 

 tion by this method, he expressed the opinion that this could not be 

 carried beyond comparatively low magnifications, because it was not a 

 case of using any proper optical system, but of producing shadow- 

 graphs by means of a "light" source and diaphragms. The actual 

 sizes of the source of radiation and the diaphragms would play a pre- 

 ponderating role if it were intended to develop magnifying power, and. 



