MR. W. CROOKES ON REPULSION RESULTING FROM RADIATION. 
291 
A 
Aluminium. 
Fig. 19. 
13 
Mica. 
ACTION OF RADIATION ON CONES, CYLINDERS, AND CUP-SHAPED YANES. 
309. Having investigated the simplest form of favourably-presented vanes, I turned 
my attention to more complex shapes, hoping thereby to obtain verifications of the 
laws which have been described in the previous pages. A pair of thin aluminium disks, 
cut half across the diameter, were bent into cones and mounted on two arms as a 
radiometer, the cones facing opposite ways. Preliminary experiments having shown 
that an effect of attraction, already noticed at pars. 267 and 268, was strongly marked 
with these cones, the following experiments were also tried. A standard candle was 
placed with the centre of its flame 3 inches from the centre of rotation of the arm 
carrying the cones. The exhaustion having been brought to about 20 millionths of an 
atmosphere, the revolutions under the influence of the lighted candle were timed. 
With no screen in front, as in fig. 20, A, the arms made 21 ‘8 revolutions a minute in 
the positive direction, — the mean of eight closely concordant observations. 
Fig. 20. 
Candle only in Elevation. 
A screen was then interposed between the candle and the concave cone, as in 
fig. 20, B, so that the radiation should only fall on the convex surfaces of the cones, as 
they emerged successively out of the shadow of the screen. The rotation became 
2 p 2 
