Metals subjected to Rontgen Radiation. 



711 



ionization-chambers. The Rontgen rays entered each box by 

 a circular window in the front face and, after passing through 

 a disk of iron-wire gauze, impinged, on a circular disk of the 

 metal to be tested. The gauze disk, G, soldered to an iron 

 ring, was held in place by three slotted pillars of ebonite, A. 

 Wires, which entered the boxes through sulphur insulators, 

 connected the gauze disks to the positive pole of the same 

 battery of a hundred cells. The metal plate, P, placed a 

 centimetre behind the gauze disk, was joined to a Wilson 

 gold-leaf inclined electroscope by a rod which was insulated 

 from the box by a sulphur plug. The tubes, C, served to 

 admit various gases, and when air was not used, thin sheets 

 of aluminium closed the windows in the boxes. 



These boxes were mounted (fig. 2) so that horizontal and 



approximately equal beams from a Rontgen-ray bulb, X, 

 entered their windows. Spring-lever keys operated by cords 

 were arranged to connect the experimental plates, P and P', 

 separately to the gold-leaf of the electroscope, to earth, or 

 together. To measure the ionization-currents created by the 

 secondary radiation between the condenser-plates, the electro- 

 scope was charged to 200 volts and was tilted at an angle to 

 give a motion of the leaf of about forty divisions in the 

 microscope-micrometer in half a minute. 



As is usual, the bulb and coil were screened by a lead- 

 sheathed box and all electrical connexions were encased in 

 metal tubes, connected to earth. At S and S', in front of the 

 windows, lead shutters were hung, which could be raised or 

 lowered by cords. When closed no appreciable ionization 

 was produced in the boxes. 



In the earlier part of the work, the rays were allowed to 

 fall not only on the experimental plates but also on a guard- 

 rino- or the inner surfaces of the box. But it was found that 



