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radiation of radium and uranium have the same value at ordinary 
temperature and at the temperature of liquid air’). The influence 
of high temperatures on the radium emanation and its transformation 
products, particularly Radium C, has also been the subject of various 
investigations. The results have given rise to differences of opinion. 
Nevertheless it would seem to be justifiable to conclude that the 
dependence upon temperature which was observed in some cases must 
be attributed to secondary phenomena of less importance, and that the 
radioactive constants of the above substances are not appreciably 
altered when the temperature is raised to 1500° ©. 
As the question is of great importance it was desirable to extend 
the results already obtained, by extending the experiments over a 
wider range of temperature and by increasing the accuracy of the 
measurements, which in the above mentioned investigations could not 
have been greater than 1°/, at the most. 
Our object was to descend to the temperature of liquid hydrogen. 
By using a compensation method we were able to determine very 
slight changes in the radiation intensity. Our measurements were 
concerned with the penetrating radiation of radium. The results, 
within the limits of accuracy which may be placed at 0.1 °/,, do 
not confirm the existence of a quickly acting influence upon the 
radiation, in consequence of this strong decrease of temperature. 
The investigations were made in the first part of 1911. The 
preliminary measurements were partly made in Paris, and partly 
in Leiden, while the final measurements took place in Leiden in 
July 1911. We intend to continue and extend the experiments, 
which is the reason of the publication having been postponed. But 
as the continuation of the work has been prevented so far by the 
long indisposition of one of us, we thought it best not to wait any 
longer in publishing our results. 
Apparatus and arrangement of the measurements. After some 
preparatory experiments we decided to use the following apparatus. 
The apparatus consists of a vacuum glass A, in which a copper 
vessel B is placed, which contains the low temperature bath. 
The vacuum glass, which is fairly wide at the top (a,) consists 
underneath of a tube-shaped portion, the length of which is about 
16 cm. and the two diameters 8,5 and 13 mm. The copper vessel 
which fits into the vacuum glass, is also provided with a tube- 
1) Becqueret, Curie, Dewar, RuTHERFORD. 
*) Curie and Danne, CG. R. 1904. Bronson, Phil. Mag. 1906. Makower and Russ, 
Le Radium, 1907. Exeter, Ann. d. Phys. 1908. Scumipt, Phys, Zeitschr. 1908. 
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