X-rays in Relation to Microscopy. By J. E. Barnard. 5 



ducted with the Kohler apparatus, Messrs. Wratten and Wain- 

 wriglit had supplied me with some very fine grain plates with 

 exceedingly thin films of gelatin. I tried these and found them 

 remarkably good, substantially better in fact than any X-ray plates 

 I had tried. The results I am showing are in most cases from 

 negatives on these plates. 



The resulting radiographs are of course of the same size as the 

 microscopic object, and photographic enlargement has to be resorted 

 to to obtain whatever magnification is possible. As I have said, 

 the photographic plate is a limiting factor, and I am therefore 

 experimenting in a direction that Mr. Eheinberg has suggested, 

 that is to make a plate that is entirely grainless. There are 

 photographic processes in which a grainless image is produced, 

 and it is on these lines I propose to proceed. 



It occurred to me that it might be possible to obtain a 

 fluorescent image and magnify that directly, and I therefore made 

 some experiments in thaf direction. The image was received 

 on a fluorescent screen and the visible image so obtained was 

 reflected at right angles to the direction of the beam of X-rays 

 by a right-angled prism, and this was picked up by a micro- 

 planar lens and so magnified. The result was not unpromising 

 except that up to the present I have not been able to obtain a 

 grainless fluorescent screen which gives a sufficiently brilliant 

 image. With certain minerals, such as Kunzite or Willemite, 

 I think it is possible that, given sufficient X-ray energy, one 

 might obtain photographs in this way. 



The question of exposure in the method described is not an 

 easy one, as microscopic objects are usually thin, and the distance 

 through which obstruction takes place is short, therefore small 

 differences in exposure make very considerable differences in the 

 result. I think from experiments I have made that it would be 

 more satisfactory in dealing with different thicknesses of objects 

 and with different resistances of the objects to X-rays, if one could 

 vary, not the exposure but the softness of the rays, using, of 

 course, softer rays for objects that are very transparent, and harder 

 ones in the case of objects of greater opacity. This, however, is 

 a point that is not easy to deal with in practice, although there 

 is an X-ray tube on the market now which enables one to produce 

 X-rays of any given quality and almost any given quantity, the 

 two factors being controlled fairly exactly. Up to the present, 

 however, I have not heard of one being made in lithium glass 

 or with a lithium glass window. 



The examples I am showing are almost entirely Foraminifera, 

 not that they are the only objects to which the method can be 

 applied, but because, owing to the kindness of Mr. Heron- Allen 

 and Mr. Earland, I had quite a wealth of this material at my 

 disposal for experimental purposes. There is, however, hardly 



