﻿Thorium and Radium Emanations. 345 



Curve C is intermediate in position. The curve for the 

 weak tube approximates more closely to the first strong tube 

 curve, and it is to be noted that although it exhibits no very 

 marked maximum, there are three points that consistently 

 indicate its presence. The last set of readings that was 

 made with the strong tube was prolonged into comparatively 

 high temperatures, and it is at once seen that there is a 

 second maximum at about 72°*5 C, and that there is a long- 

 portion of the curve between 115° C. and 143° 0. during 

 which the fraction of the emanation condensed remains 

 constant. 



The results of this experiment show (1) that different 

 tubes, in general, have different condensation curves, (2) 

 that as the concentration of the emanation diminishes it 

 becomes easier to condense, and (3) that there exist two 

 maximum points, one at — 161° C. and the other at 

 -72°-5 G. 



Luminosity Experiments, 



The existence of at least one maximum point was then 

 studied in another way. A good many years ago, Rutherford 

 noticed that if a tube containing radium emanation was 

 partially immersed in liquid air, the greatest intensity of 

 the luminosity occurred just above the surf ace of the liquid 

 air, and that as the level of the liquid air was raised the 

 ring of greatest intensity was raised as well. This expe- 

 riment was repeated by supporting a tube, containing 14 

 millicuries of emanation with a very small quantity of 

 other gases, on a cork floating in liquid air. The ring 

 of brightest intensity was obtained, but it was found that, no 

 matter how long the tube was kept in liquid air, all the 

 luminosity could not be obtained on this ring. There was 

 still a large fraction scattered over that part of the tube 

 beneath the level of the liquid air. It was proved that this 

 ring was not due to a collection of ice nor due to a particular 

 state of the glass, because the ring persisted after the whole 

 tube had been warmed to room temperature. To test whether 

 the effect was due to some electrical condition of the glass 

 which would cause an accumulation of the active deposit in 

 this particular region, even although there was no concentra - 

 tion of the emanation, a glass tube, silvered on the inside, was 

 filled with the above mentioned quantity of emanation. If 

 the effect had been due to electrical causes, the silver would 

 have dissipated any charge that had accumulated in one 

 region. 



The ring of intensified luminosity was still observed. The 



