288 Mr. S. Skinner on the 
place at our disposal a method of reinforcing sounds possessing 
some special advantages, and may prove capable of increasing 
faint sounds so that many can hear them at once, to a degree 
beyond that attained by any other method at present known. 
Eton, Oct. 1903. : 

SSS ES SSS - $$ ———e ee 
XXX. The Photographic Action of Radium Rays. By 8. 
SKinner, J/.A., University Demonstrator in Experimental 
Physics at the Cavendish Laboratory, Cambridge *. 
i he is well known that a photographic plate by exposure to 
. Radium rays is affected in such a way that the plate 
develops similarly to its development after exposure to light. 
The following experiments are an attempt to answer the 
question : Are the actions the same? As far as can be seen 
by eye, plates exposed to the two agents appear on develop- 
ment to be darkened in a similar way, and we may conclude 
that the final result of the actions and of the development 
is the same. I have attempted to obtain information of the 
intermediate stages, and some of the experiments described 
below appear ‘to indicate that only slight differences occur in 
these early stages. I shall describe the experiments in the 
order in which they may be best understood, although this was. 
not the order in which they were made. 
A plate, inclosed in two envelopes of paper, one red and 
the other black, was placed under a capsule containing 
10 milligrammes of radium bromide at a distance of 1 centi- 
metre from the plate for periods of time varying from half a 
minute to 48 hours. A different part of the plate was. 

against a flame. Barrett and Tyndall were apparently the first to notice 
that a sensitive flame sometimes reproduces the tones by which it is 
affected. In 1875 Decharme found that carbon dioxide blown through 
a jet against a flame gave a feeble effect, and attributed this to the 
decomposition of the CO,—a chemical explanation. He also found 
that pure oxygen gave only a feeble effect in comparison with air, and 
that nitrogen gave no effect at all. Mr. Bell himself, by boring a 
small hole in a telephone-plate, and forcing through it, at a gentle 
pressure, a stream of air which impinged on a small flame, reinforced 
the otherwise inaudible sounds of the telephone till they could be dis- 
tinctly heard over a small room. The explanation of the reinforcement, 
—founded by Mr. Bell on a long series of delicate and beautiful expe- 
riments, including the measurement of the relative pressures at different 
points in and near the jets,—seems to be a purely physical one. The 
actual experiments as described in the present paper are, however, new, 
so far as the author can ascertain—though Mr. Bell has experimented on 
the use of flames in connexion with the graphophone, and took outa 
patent thereon in 1886. 
* Communicated by the Physical Society: read January 22, 1904. 
