Ionization Curves of Radium. fou 
tubes which were only 1 cm. high, so that it might be 
possible to bring the radium close to the chamber: at the 
longer ranges the curves were therefore too wide to fall 
completely within the entrance to the chamber. The portion S 
represents the ionization due to the first change, and is always 
in excess of the others*. It might appear that after six days 
P, Q, and R ought to be more nearly of the width of S; but 
it is probable that the emanation which is formed does not all 
remain occluded in so thin a layer. We know, in fact, that 
it is always passing into the atmosphere. When a dish has 
been made red hot, the radium, as Rutherford has observed, 
retains its emanation better. In fig. 4 (p. 732) is shown the 
ionization curve of a dish five days after being so heated ; and 
it will be observed that P, Q, and R are now nearly equal toS. 
The portions P and 8 are easily separable from the rest of 
the curve, and clearly represent different sets of rays. The 
portions @) and R are not so clearly distinguishable from 
each other. When the cones of rays are wide, as in the case 
of the experiments represented in fig. 2, the break between 
the two portions is not at all clear ; but when the curves are 
narrower, as was the case in fig. 1, the break is better 
shown. We have been over this portion of the curve many 
times, using different dishes and different sets of tubes, and 
we have always found the dip more or less pronounced. 
When a dish is raised to a red heat the portions Q and R 
disappear, whilst P subsequently decays in great part. This 
is what should occur supposing that «) and R represent the 
rays from the emanation and the first induced activity, 
* We give a table of the figures from which one of the curves in fig. 3 was 
plotted : it would be tedious to give the figures in every case. 
Distance from | Distance from 
Radium to Leak Radium to Leak 
Chamber. per second. | Chamber. per second. 
WES" crc. "535 WY AP ANSET <. ctest | vate aici 520 
oc ae ee 520 i SCD) | . se .ntess “880 
(56/5 ee: 6) | DAO) vexchapars ‘930 
52) Aree ‘560 Bee) samen "975 
O2P) viststhas ‘615 SUS ps cheer. 1125 
ODO eccnosnpe "630 BBD Gek, shies 1-435 
ESO vad se ata LoTe\0) gh | RSet Rehr ert ie eee 1-425 
Me we | edie sieresine "520 BOOP et si 1-665 
BIG a oi. ses 640 A, 15 Mes BOERS 1-770 
PED | out. 40 640 | Paper ...... Mae Hea gee TOAD 
OD 5 sashes 640 DEBS Y 4 oe Sons 1-765 
BUD kas ves 620 DU Drees ope: 1-690 
BPA chk ance ‘650 TSG |S eeean 1-600 
APZD seein dene ‘700 IGDY) Anil. 15385 
BOD) sec carte “755 MAD OT cise ead 1-470 
a8 .. 800 TDG sei-ccies oes 1-430 
