ME. W. CE00KE3 ON EEPULSION EESULTINQ EEOM E ADI ATI ON. 
347 
of heat to it from that side, and therefore allows an excess of heat to fall upon it from 
the opposite side. 
The same radiometer that I used in the experiments with boiling water (155) was 
mounted with a candle the same distance off as before, so that one revolution took place 
in one minute. A lump of ice was now brought within half an inch from the bulb on the 
opposite side to the candle. The revolutions got slower, each arm as it passed seeming 
drawn towards the ice, and having a difficulty in moving away from it. At last the 
movement stopped altogether, an arm pointing direct to the ice, and being apparently 
held there by a powerful attractive force. Bringing the candle nearer caused the arms 
to oscillate a little ; and when it was almost close to the bulb the force of the light 
overcame the action of the ice, and the arms revolved again, but irregularly and with 
jerks, the disks moving quickly to the ice and leaving it with difficulty. In this action 
of ice no preference was noticed for either the black or white surface. 
159. A very delicate radiometer, in 2-inch bulb (152), was placed in a light just suf- 
ficient to see it distinctly by, but not enough to cause it to move. I then came out of 
a warm room and stood near it. In a few seconds it began to move slowly round, 
but the motion was negative, i. e. the black disks advanced instead of retreated — 
the action of the radiation of low intensity from my body being apparently to repel the 
white surface more than the black. On moving away from the instrument the rotation 
gradually stopped. I now came near it again, and held one hand an inch from the bulb. 
Botation soon commenced, but still in the reverse way. These experiments were 
repeated several times and on different evenings with the same results. 
160. When the instrument was at rest I came quickly to it, and gently breathed on 
the bulb. There was a slight movement in the normal direction, but this stopped 
directly, and the arms commenced to revolve the negative way, and kept on in the same 
direction for more than a minute, performing three or four complete revolutions. 
161. A glass shade 4 inches diameter was held over a gas-flame till the air inside was 
warm and the inner surface dim with steam. It was then inverted over the radiometer. 
Negative rotation commenced, and kept up for several minutes. 
The glass shade was then dried inside, and heated uniformly before a fire, until it had 
a temperature of about 50° C. It was then inverted over the radiometer. Negative 
rotation instantly commenced, and kept up with some vigour for more than five minutes, 
diminishing in speed until the shade had cooled down to the temperature of the sur- 
rounding air. 
162. The same experiment was repeated, and whilst the arms were in full rotation a 
lighted candle was slowly brought near it. When 3 feet off the negative rotation 
slackened. When the candle was about 2 feet off the arms became still, and when nearer 
than 2 feet the instrument rotated normally. The antagonism between the action of the 
hot shade and the lighted candle was perfect ; by moving the candle to and fro it was 
easy to cause the radiometer to move in one direction or the other, or to become still. 
These experiments were repeated many times, always with the same result. The perfect 
