473 
1908-9.] A Simple Radioscope and a Radiometer. 
apparatus so as to produce ions in the moist air, he showed that these ions 
became active centres of condensation ; and he also showed that the super- 
saturation necessary to make them centres of condensation was the same 
as that required for the nuclei always present in the air. He further 
showed that these ions were electrically charged, some with positive and 
some with negative electricity, and that they could be removed by an 
electric field, but, so far as his experiments went, there was no evidence to 
show that the nuclei always in the air carried any charge. 
Turning now to the new instruments, fig. 1 shows the arrangement of 
the radioscope which will be described first. A is a U-shaped glass tube 
about 2 cm. internal diameter, in which the air undergoes the compression 
and expansion necessary for causing condensation in the dustless air. The 
U tube is partly filled with water, and the upper part B is the expansion 
chamber in which the observations are made. The other side of the U tube 
is connected by means of the india-rubber tube C with the india-rubber 
ball D. This ball can easily be obtained in any chemist’s ; its fittings are 
removed, and the short piece of metal tube E put in their place. The tube 
E is fixed to the board F, so as to keep the ball in its place in the centre of 
the hollow cut out in the surface of F. The lever G turns on the hinges 
H. When G is pressed down it compresses the air in D and in the chamber 
B of the U tube. K is a strip of spring brass bent into a segment of a 
circle. On K slides the stop J, which can be fixed at any point on K by 
means of the pinching screw I. On the outer end of the lever G is fixed 
a small piece of metal L, and when the lever G is pressed down to com- 
press the air in the ball D it engages with the stop J and keeps the ball 
compressed until it is desired to expand the air in the test chamber B, when 
the spring K is drawn back, and the lever G being disengaged the ball at 
once expands and relieves the pressure in B. M is an india-rubber cord for 
preventing the lever G being forced too far over. 
This arrangement of compressing and allowing the air to expand is not 
the usual one in experiments of this kind, as it is customary to expand the 
air by means of a pump or similar arrangement. The method shown, 
however, has some advantages over the pump. There is no leakage in the 
working parts, and the simple act of pressing down the lever G is all that 
is required, while the catch J keeps the pressure on till the temperature 
and vapour pressures in the expansion chamber have adjusted themselves. 
It has, however, one defect due to the heat developed by the compression. 
On the first compression being made the air in the ball and tube gets heated, 
and some of this heat escapes before expansion is made, and unless con- 
siderable time is given before the next compression, it will be made at a 
