618 Hon. R. J. Strutt on the 
‘The evidence that y rays are Rontgen rays is two-fold :— 
(1) The y rays are not deflected by a magnetic field. 
(2) In the changes of radium the @ and y rays always 
appear together and in the same proportion. This 
result is to be expected if the y rays are produced by 
the . 
In any case the present paper removes an objection to this 
view. It is true that methyl iodide remains as a marked 
exception to the density law, but it is probable that harder 
rays than those employed would bring this vapour into line’ 
with others. 
In conclusion, I have to thank Professor Rutherford for 
suggesting the experiment, and for his encouragement and 
advice in carrying it out. 
McGill University, Montreal, July 1904. 
LXI. Notes on the Radioactivity of Various Materials. 
By Hon. R. J. Strutt, Fellow of Trinity College, Cambridge*. 
[* this note I shall put together some rather fragmentary 
observations on the presence of radium in various 
materials. The note may be regarded as supplementary to 
a paper published in the Proc. Roy. Soc. Ixxiii. p. 192. 77 / 
The method of experimenting was the same as is described 
in that paper. The emanation was extracted from the sub- 
stance by heat, and introduced into an electroscope: the rate 
of leak was read in the usual way. 
The following Table (p. 619) gives the results for the various 
materials, on the same scale as in the former paper. These 
were not, for the most part, carried out more than once; and 
must not be regarded as much more than indications. 
1. This refers to a hard deposit, left in the lead pipes of 
the ancient Roman baths. It contains less iron than the 
modern deposits, and is much less radioactive. It would be 
rash to draw any positive conclusion from the latter fact, for 
we are ignorant of the precise conditions under which the 
Roman deposits were formed. But the idea suggests itself 
that the radium has been here separated for 2000 years from 
its parent (uranium ?), and is consequently much diminished 
in activity. I have tested the most active of the modern de- 
posits, but found no uranium in 100 grams of it. One milligram 
should have been easily detected. 
2-5. Lord Blythswood and Mr. Allen have found the gas 
of the Bath springs to contain emanation. I wished to com- 
pare the activity of this gas with that of the other materials, 
* Communicated by the Author. 
