X-Rays and Scattered X-Rays, 29 1 
of the type described in previous papers — modifications of 
those devised by C. T. R. Wilson. Their thin paper and 
aluminium faces were against the apertures, which were of 
dimensions 3*2 x 5 cm. and 5x5 cm., and were placed 
symmetrically w T ith regard to the carbon at a distance of 
21 centimetres. 
With this arrangement the radiation from each atom before 
entering one electroscope had to travel approximately the 
same distance in carbon and air as that entering the other. 
The intensities of the secondary beams entering the electro- 
scope were then proportional to the intensities of radiation 
from the atoms in the two directions RA X and RA 2 . One of 
these RA X made only a small angle with the axis of the 
primary beam, while the other RA 2 was perpendicular to 
that axis. 
By first placing a sheet of copper in the position R, it 
was found, by alternately placing one electroscope in the two 
positions A 1 and A 2 , that there was no appreciable difference 
between the intensities of secondary radiation from copper in 
the tw^o directions. 
This is what was expected from the results of previous 
experiments on copper, for it was found that when a polarized 
primary beam fell on copper the intensities in the two 
principal directions at right angles were equal, indicating 
that the copper radiation was equally intense in all directions 
whatever the position of the plane of polarization and direction 
of incidence of the exciting primary beam. The character 
of the secondary radiation from copper had also been shown 
to be approximately independent of that of the primary 
producing it. The equally intense copper radiations were 
therefore used to standardize the two electroscopes afterwards 
used in place of the one. 
Thus in one experiment after correction for the normal 
ionization in the electroscopes, for the effects of the secondary 
rays from air and for the ionization that may have been pro- 
duced by very penetrating primary rays in the electroscopes, 
the deflexions of electroscopes A x and A 2 were 12*5 and 
18*05 respectively when copper was the radiating substance. 
Xow as these were due to equally intense beams, the 
deflexion of 12*5 in electroscope A 1 w r as equivalent to 18*05 
in A 2 . When the copper was replaced by carbon the 
deflexions were 7 and 5*2 respectively, and by repeated 
observations 7*9 and 5*95. Taking the average of these we 
have 7*45 and 5*575. If the electroscopes had been equally 
