612 Mr. A. S. Eve on the Ionization produced in 
further screened from the direct rays from = focus of bas 
bulb by a block of lead 4:7 ems. thick. } 
Fig. 2 
One of the brass cylinders was filled with air ‘at barometric 
pressure, and served as a standard, The variations in the 
intensity of the rays from the bulb rendered such a standard 
necessary. The other cylinder was exhausted by a pump 
and filled with the required gas which passed through glass- 
wool and phosphorus pentoxide. In working with the 
vapours of chloroform, carbon tetrachloride, and methyl- 
iodide, readings were taken at various pressures less than 
the vapour- -densities. The natural leaks were deducted from 
the deflexions due to the ionization currents, and the readings 
of the exhausted electroscope were reduced to a percentage 
of those of the standard electroscope. 
Arrangements were made to take observations of the values 
for the y rays. The radium was sealed in a glass tube 
placed. in a hole in a cube of lead suspended behind the 
thick lead screen. The rays therefore passed through 1 cm. 
of lead before reaching the lower large cylinders, and through 
more than 6 cms. in order -to strike the small electroscope 
above. In the early experiments some irregularities were 
traced to convection currents caused by the heat from the 
electric lamps when the lead vessels were removed. The 
heat was screened by two sheets of plate-glass 6 mm. thick 
and by a sheet of paper. The Rontgen rays therefore 
penetrated the walls of the bulb, 12 mms. ‘of glass, 1°7 of lead, 
and 1°8 of brass. Care was taken to employ a saturating 
E.M.F. 
Réntgen hays. -: 
The following table shows the values obtained in éiie 
present experiment as compared with those previously 
recorded for soft rays :— 
