MR. W. CROOKES ON REPULSION RESULTING PROM RADIATION. 
367 
Deflection of index ray of light on millimetre-scale 1100 millims. 
from mirror. 
Distance of candle 
from disks. 
Screen interposed. 
White disk. 
Reduced to Black=100. 
IJlaCK CllSK. 
Black. 
White. 
sort millims. ... 
Nothinp - 
192 
122 
32 
100 
16-7 
900 „ 
21 
100 
17-1 
1200 „ 
62 
10 
100 
16-1 
500 „ 
Cell of water 
80 
7 
100 
8-7 
500 „ 
Alum plate 
100 
8 
100 
8-0 
500 „ 
,, solution 
76 
7 
100 
9*2 
500 „ 
Ammonia gas, 6 in. thick, 
and cell of water 
79 
7 
100 
8-8 
800 
Ammonia gas alone 
190 
31 
100 
16*3 
201. The lower disk was removed and replaced by a disk of pith thickly coated 
on one side with pure precipitated carbonate of lead. The disk weighed 0499 grain, 
the counterpoise weighing 0‘530 grain. 
After complete exhaustion, the results of various experiments are shown in the 
following Table : — 
Distance of candle 
from disks. 
Screen interposed. 
Deflection of index raj of light on millimetre-scale 1100 millims. 
from mirror. 
Black. 
Carb. Lead. 
Reduced to Black =100. 
Black. 
Carb. Lead. 
800 millims 
Nothing 
130 
17 
100 
13’0 
500 „ 
Iodine in disulphide of 
carbon 
127 
9-5 
100 
7*5 
Instead, therefore, of carbonate of lead being a good absorber of the rays which 
produce motion, it is a better reflector than a plain white pith surface, owing probably 
to its superior whiteness. 
202. Another black surface was now sought for to compare with the standard disk. 
Pith coated with precipitated iodide of palladium was employed. The disk weighed 
Q-460 grain, and the counterpoise 0‘491 grain. The results were : — 
Standard Black. 
Iodide of 
Palladium. 
Reduced to Black = 100. 
Black. 
Iodide of 
Palladium. • 
70 
61 
100 
87-3 
203. Plates of alum and of rock-salt were successively introduced into the appa- 
ratus, to be compared with the standard black disk. The apparatus was, however, not 
sufficiently sensitive to enable me to make satisfactory comparisons. The average of 
3 e 2 
