481 
1908-9.] A Simple Radioscope and a Radiometer. 
fig. 1 by means of the tube C. The inside of the chamber, where possible, 
is covered with blotting-paper, which is kept wet for the purpose of 
saturating the air. The tube C is attached to the compression chamber B 
by means of the union joint D. This opening is required for the purpose 
of cleaning the cover glass and the micrometer, and also for wetting the 
interior of B. After the air has been compressed and expanded the drops 
fall on the micrometer and are counted with the aid of the lens L, while 
the illumination is effected by means of the spot-mirror M, either daylight 
L 
or artificial light being used. As the thick walls of the chamber B offer 
considerable obstruction to the rays from the radioactive substances, a 
window A is cut out on one side of the chamber and covered with 
aluminium 025 mm. thick. 
Fig. 3 shows the arrangement of the apparatus when fitted together. 
The part R, however, may be omitted, as it is for a special purpose, and will 
be described later. Between the compressor and the chamber B is intro- 
duced a pressure gauge P. This gauge is, however, not necessary, but is con- 
venient, as it shows whether all the joints are air-tight or not and the com- 
pression keeping constant. The gauge is not necessary for setting the 
amount of compression required, as that is obtained by trial. After the 
glass surfaces in B have been cleaned and the sides wetted and all con- 
vol. xxix. 31 
