X-rays in Relation to Microscopy . By J. E. Barnard. 3 



It appears probable that in the present state of knowledge no 

 advance in Microscopy will be made on optical lines, but if it 

 is possible to utilize some new source of energy, then there is 

 some hope that advances may be made — advances, I venture to 

 say, that are at present beyond our imagination. We shall, as a 

 result, be able to go far beyond the limits that at present seem so 

 impenetrable. 



On reading carefully the records of the work referred to on 

 X-rays and crystal structure, I was at once impressed with the idea 

 that, if we could in any way use X-rays as a source of energy for 

 microscopical work it would take us a great deal further. X-rays 

 are in order of wave-length something like one-thousandth that 

 of the Schumann waves in the ultra-violet spectrum. Assuming 

 that some means of utilizing them to the full is found, it should 

 be possible to demonstrate structure and to obtain resolution that 

 is inconceivable by any method at present available. 



I talked the matter over with Mr. Eheinberg at this time, and 

 he was so impressed with the possibilities in this direction that 

 I had the advantage of his collaboration in some preliminary 

 experiments which we agreed to attempt. Unfortunately, he 

 became engaged in other and more important work, and was 

 obliged — temporarily only, I hope — to relinquish his share in the 

 experiments. 



It is at once only fair to say that so far as any practical result 

 goes we did not achieve very much. It was a question, at first, 

 of repeating the early experiments that had been made by the 

 observers mentioned, and by Bragg in this country. We were 

 able to get some reflected X-ray images from crystal surfaces 

 and from mica films, and by using curved mica films we suc- 

 ceeded in changing the form of a reflected beam of X-rays. The 

 problem to be solved at the present time is to find a method of 

 expanding or contracting a beam of X-rays in the manner that a 

 lens alters the form of the wave-front with ordinary light. If 

 means could be discovered to effect this, not on the face of it an 

 insurmountable obstacle, then X-rays have characteristics that 

 would make them by far the most valuable source of energy at 

 present known in microscopic work. If we consider the fact 

 that X-rays are selectively absorbed by so many substances, we 

 realize that even at present we are in a position to utilize them, 

 apart from the question of obtaining greater magnification and 

 resolution. That being the case, I was interested enough to make 

 some experiments to determine how far one might be able to go in 

 obtaining direct radiographs of microscopic objects, enlargements 

 being obtained by photographic means, and I venture to think the 

 results are not uninteresting. 



It is perhaps advisable briefly to indicate the conditions under 

 which X-rays are produced. An X-ray tube, as ordinarily con- 



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