672 Prof. Bragg and Dr. Madsen : An Experimental 
positive and beccme a secondary cathode or /3 ray would be 
lost to measurement as a 7 ray ; and we should thus have an 
explanation of how the 7 rays are " absorbed/' and why the 
absorption follows an exponential law. And in the same 
way, if a /3 particle picked up a positive it would disappear 
from view as a ft particle ; it would be " absorbed." 
Although we have made a few experiments with magnetic 
fields, we have not yet come to any conclusion as to whether 
or no there are 7 pairs which have become loosened in the 
attachment of positive to negative, forming a softer and 
more ionizing radiation. Their existence might be suspected, 
since there is an analogous effect in the case of X rays ; and 
probably they would be found more at the back o£ the 
penetrated plate than in front o£ it. 
A few further experimental illustrations are shown dia- 
grammatically in figs. 5 and 6 with the explanations 
attached. 
Fig. 5. — The upper figure shows the general arrangement. 
The lower figures are diagrammatic, and show the currents 
for different arrangements of the Pb and Al at the bottom of 
the chamber, and at the top with the exception of the plate 
through which the 7 rays enter. Inverting the top plates 
makes little difference when the upper of the two plates at 
the bottom is Al ; but an appreciable difference when it is 
Pb, because in the latter case a good deal of secondary 
radiation is thrown up by the Pb, and there is a tertiary 
from the top plate. 
The same, when the conical opening is completely filled 
by a Pb stopper : — 
12-6 12-6 17-7 18*3 
The differences show the effects of those rays only which 
are stopped by the Pb stopper : — 
27-7 28-7 39-9 44-7 
These show the effect of inverting that portion only of the 
top plate where the 7 rays enter. Three Pb plates = *55 cm.; 
Al plate=*16 cm. 
The same, with Pb stopper inserted : — 
14-1 14-7. 
