Lonization Curves of Radium. 733 
received a long expected Dolezalek electrometer by this 
week’s mail, and hope to work more quickly and accurately 
with its aid. Heating the dish more moderately seems to 
show that R is the emanation and Q the first induced activity. 
It will be observed in most of these curves that there is 
a curious return towards the vertical axis: it is best shown 
in the lower portions of P and 8. We do not see that 
there is any other than one possible explanation, viz., that 
Fig. 5. 
(o>) 
Gt: 
Gy 
™ 
DisTANCE /N CM. FROM RADIUM TO IONISATION CHAMBER. © 
“4 A 
Ac porn 2) 
LEAK OF ELECTROMETER /N MM. DIVISIONS 
OF SCALE PEFR SECOND. 
I. Curve 30 hours before heating. II. Curve after raising to red heat. 
»!* TIL. Curve about 30 minutes later. 1 §28R 
the « particle is more effective at the end of its course.’ This 
is not surprising. The disturbing influence of the @ particle 
in its transit through an atom must become greater as the 
speed diminishes. The diminution is not likely to be great 
except at the end. This is indeed shown by the curves. 
Theoretical considerations based on a somewhat insufficient 
hypothesis show that the effect should be inversely propor- 
tional to the energy of the moving particle; but in the case 
of the 8 rays Durack has shown that the influence of change 
of speed is not so great as this. It is possible that it is only 
at the end, when the change of velocity is very great in pro- 
portion to what remains, that the influence of this cause is 
Phil. Mag. S. 6. Vol. 8. No. 48. Dec. 1904. 3H 
