X-Rays and Scattered X-Rays. 293 
intensity of the beam RA 2 depends to this extent on its 
position with regard to the cathode stream in the X-ray 
tube. The above ratios were obtained when the beam RA 2 
was parallel to the cathode stream, and therefore have the 
maximum values. The intensities o£ secondary radiation in 
directions RA X and RA 2 when easily absorbed primary rays 
were used, were therefore in ratios varying from 2 : 1 to 
2 : 1*2, i.e. from 2 : 1 to 1*66 : 1, according to the position of 
the plane of polarization of the partially polarized primary 
beam. 
For an unpolarized primary beam, the ratio of intensities 
in the two directions RA T and RA 2 would therefore be 
approximately 1*85 : 1. 
The results of these experiments in this way showed that 
the ratio of the intensities of secondary rays from carbon in 
the two directions indicated varied from about 1*85 : 1 with 
very soft rays to about 1*45 : 1 for penetrating rays. Now 
the first ratio is of the order — probably a little less — that 
might have been expected if we assumed perfect scattering 
on the sether-pulse theory, the rays entering electroscope A 1 
making a small angle with the direction opposite to that of 
primary propagation, and most of those entering A 2 being 
not quite perpendicular to the direction of propagation of 
the primary. 
On the other hand, on the neutral pair hypothesis the 
ratio should be roughly 7 or 8 : 1. This, however, is on the 
assumption that a pair rotating in one plane continues even 
after ejection from an atom which it strikes to rotate accurately 
in the same plane. If we admit any deviation from this, 
then the ratio of intensities becomes less than the above. 
But the polarization which exists in a secondary beam from 
carbon is sufficiently complete to show that if the effects are 
to be explained on such an hypothesis, the behaviour of the 
pairs must approximate very closely to this ideal, and con- 
sequently the ratio of intensities in the two directions RA 2 
and RA 2 could not possibly have been lower than 4 : 1 or 5 : 1. 
We thus have what appears to be most conclusive evidence 
against the " neutral pair " hypothesis, and the most con- 
vincing verification of the sether-pulse theory that could be 
given by such experiments. 
Not only is there perfect agreement between theory and 
experiment here, but experiments showed that where the 
secondary rays were otherwise found to be less purely a 
scattered radiation judged by their penetrating power, and 
by polarization experiments, there was also a reduction of 
the ratio of intensities discussed in this paper — the result to 
be expected on the pulse theory. 
