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Mr. J. Crosby Chapman on 



sheets o£ the order of thickness required by the experiment. 

 In addition, it has often been proved that carbon is a most 

 inefficient corpuscular radiator, so much so that in all ex- 

 periments where this type of radiation from the walls of the 

 ionization- chambers is to be minimised, carbon in the form 

 of paper is used for this purpose. So that, instead of air or 

 C0 2 separating the different portions of the radiator, which 

 is in the form of gold leaves, it is possible to use thin paper. 

 Apparatus. — The apparatus, with a few modifications, was 

 similar to that used in previous experiments. 



Construction of Radiators. 



The two radiators, the efficiency of which as fluorescent 

 X-ray producers it was required to determine, were con- 

 structed as follows: — 



Ksr. 1. 



Radiator I. Radiator II. 



Gold leaves separated. Gold leaves together. 



Continuous line=sheet of paper. 

 Dotted lines =gold leaf. 



The important point to notice is that both radiators con- 

 sisted of the same mass of gold and paper, namely, seven 

 gold leaves and sixteen paper sheets, the sole difference 

 between the two radiators being the relative positions of the 

 gold and the paper. 



In radiator I. we have first two sheets of paper then a gold 

 leaf, then again two sheets of paper and another gold leaf, 

 and so on till the seven gold leaves and the sixteen paper 

 sheets are all used. In radiator II., however, we take first 

 eight sheets of paper, then seven gold leaves altogether, 



