Production of Fluorescent Rant gen Radiation. 363- 



followed by another eight sheets of paper. Each of these 

 two arrangements of gold leaf and paper was mounted 

 between thick aluminium frames. In this way the leaves 

 and paper were gripped around their edges, and with a little 

 care in fixing the outer paper sheets with shellac on to the 

 frames, it was arranged so that the paper in each case was 

 stretched tightly across the frame. The two aluminium frames 

 were pressed together in a vice and melted wax was run 

 around their edges, so that the two remained tightly pressed 

 to one another. The thickness of the effective parts of each 

 radiator, that is, in the centre, where the X-rays struck and 

 where there was no aluminium, was such as could be accounted 

 for by the presence of the paper sheets alone. The desira- 

 bility of leaving no air-gaps will become apparent in the 

 calculations. A third radiator was made in a similar manner 

 containing only the sixteen paper sheets. 



It may be added here, that alternate gold leaves, taken 

 from the same book, were used to form the radiators I. and 

 II. respectively. It will be noted that, owing to the arrange- 

 ment of the paper and the gold leaves and their small 

 absorption, the gold fluorescent radiation was absorbed to 

 approximately the same extent in the two cases. 



Object of this Construction. 



Imagine now the same primary beam of X-rays to be 

 passed through radiator I. and radiator II. successively. 

 Consider, first, radiator I : suppose there is being produced 

 in the central gold leaf 8 a certain amount of corpuscular 

 radiation. It will be shown later that the greater part of 

 the energy of these corpuscles escapes from the leaf. This 

 is the sole assumption made at the present, and it is proved 

 by actual experiment later in the paper. Then in radiator I. 

 the corpuscles which emerge from the central leaf 8 will at 

 once pass into paper, where they will be totally absorbed, so 

 that their existence as regards acting on gold atoms is at an 

 end. Whereas in radiator II. corpuscles produced at 8 will 

 have to spend practically the whole of their energy in the 

 gold leaf itself. So that, while in the case of radiator I. the 

 corpuscles spend a large part of their energy in the paper,, 

 in the case of radiator II. the corpuscles spend almost all 

 their energy in the gold. So that, quite apart from any 

 meaning "absorption" may have, we should expect, if the 

 expelled electrons by bombarding other gold atoms produce 

 secondary X-radiation, that the radiator II. would be more 



