MR. W. CROOKES OK REPULSION RESULTING PROM RADIATION. 
125 
at high exhaustions, produced slight electrification, which caused the two disks to be 
drawn together. This was remedied by connecting the lead to earth by a fine wire, e. 
A candle was used as the source of radiation ; it was set a measured distance from 
the blacked disk. Its rays were cut off by water and opaque screens, except at the 
time of trying an experiment; and all extraneous radiation, or interference from the 
warmth of the body, was cut off by water screens and black velvet placed around. 
The scale to receive the reflected index of light was 3 feet from the mirror. A 
movement of the blacked disk to the extent of 1 millim. produced a deflection of 
32 divisions on the scale. 
457. Preliminary experiments showed that it was not necessary to rarefy the air in 
this apparatus to get repulsion. By moving the control magnet sufficiently far off to 
secure great sensitiveness, and putting the candle 120 millims. from the blacked disk, 
the following results were obtained at ordinary atmospheric pressure :— 
T. = Tension in millimetres of the gas in the apparatus. 
C. = Distance in millimetres of the candle from the blacked disk. 
S. = Distance in millimetres separating the screen and disk. 
F. = Force of repulsion represented by the degrees on the scale covered by the first 
swing of the luminous index. 
T. 
C. 
S. 
F. 
millims. 
millims. 
millims. 
748 
120 
1 
367 
2 
207 
4 
11-0 
5 ) 
95 
8 
3-5 
Plotted on a curve, the results in columns S and F give the line shown in fig. 28. 
Fig. 28. 
458. The repulsion being so decided at atmospheric pressure, the apparatus was 
