Gaseous Mixture shy Rontgen and Corpuscular Radiations. 833 



The corpuscular radiations were, however, of the variable and 

 uncertain type set up by heterogeneous beams of Rontgen rays 

 and the gases and vapours ionized were not the most suitable 

 for our purpose, as the following considerations will show. 

 In our experiments the corpuscular radiation studied was 

 that emitted by thin sheets of gold traversed by homogeneous 

 beams of X-rays. As is well known, the velocity of the 

 ejected corpuscles depends not on the element emitting 

 them *, or on the intensity of the Rontgen radiation causing 

 their ejection, but simply on the absorbability — (or wave- 

 length) — of this Rontgen radiation. In these respects as in 

 many others the properties of Rontgen radiation are identical 

 with those of ultra-violet light. 



The ionization-chamber used in these experiments consisted 

 of a shallow metal box 1 centimetre in depth, with square 

 ends of about 10 centimetres edge (see fig. 1). Large square 



Fig. 1. 



ro electroscope - 4 j *"" -. 'j ' \ -j <■ |,'- ' »"""' 7 = To Gm Chamber 



i <>ji ' 

 i. 1 • 



1,/p 



apertures were cut in these metal ends, and carbon plates 

 about 2 mm. thick were placed on the flat ends over these 

 apertures, and the whole chamber made air-tight by means 

 of wax poured on the outside of the plate, and round the 

 edges. The carbon plates could be easily detached and 

 refixed in the same position. A square electrode of aluminium 

 wire crossed by meshes of extremely fine aluminium thread 

 was placed in a plane midway between the two end faces. 

 This electrode was connected through an insulating ebonite 

 plug to the gold-leaf system of an electroscope. When the 

 homogeneous X-radiation from a secondary radiator was 

 allowed to fall on one face of the ionization-chamber, the beam 

 which traversed the carbon window passed within the outer 



* It is possible that the velocity depends to a slight extent on the 

 element, as it appears to do when ultra-violet light causes the ejection. 

 No such dependence has been established in the case of X-rays. 



