QUEKETT MICROSCOPICAL CLUB. 19T 



produce lenses so nearly perfect that they almost reach the 

 theoretical limit. The only method by which any substantial 

 increase in numerical aperture, and consequent resolution, has 

 been obtained is by the use of ultra-violet light. By this means 

 resolution has been increased beyond the utmost that can be 

 obtained in any other manner. When reading the records of 

 the work done on X-rays, I was impressed with the idea that if 

 we could in any way use these rays as a source of energy for 

 microscopic work it would take us a great deal farther. Assum- 

 ing that some means of utilising them to the full is found, it 

 should be possible to demonstrate structure and to obtain resolu- 

 tion that is inconceivable by any method at present available 

 The slides Mr. Heron-Allen has kindly exhibited were the out- 

 come of 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. The 

 method adopted for producing the radiographs is quite simple. 

 The tube used is provided with a lithium glass window, so that- 

 the soft X-rays are freely transmitted. Ordinary glass ob- 

 structs these very seriously. The tube is enclosed in a lead- 

 covered box, so that the rays cannot pass out except in the 

 desired direction. There are two or more lead diaphragms 

 fixed in a tube placed above the lithium glass window, each 

 diaphragm having a small central hole. By this means an 

 approximately parallel beam of X-rays of very small cross- 

 section is transmitted. The object is placed in the path of this 

 beam, which passing through it impinges on a photographic 

 plate placed in actual contact with the object. The resulting 

 radiograph is of course the same size as the microscopic object ^ 

 (unmagnified), and the enlargement to lantern-slide dimensions,, 

 or whatever magnification may be desired, is obtained by 

 ordinary photomicrography. One of the difficulties encountered, 

 was the necessity of obtaining plates with a sufficiently fine^ 

 grain to record the extremely minute details and to allow of 

 effective enlargement. But that this and other problems had. 

 been successfully overcome was apparent from the beautiful 

 series of lantern photographs that had already been exhibited." 

 The lecture was followed by an interesting discussion in which, 

 the President and Messrs. Hilton, Ainslie and Blood took part,, 

 and by a hearty vote of thanks which showed the appreciation. 



