458 
MR. TV. CROOKES OK THE SUPPOSED 
Considering that it would be almost impossible to get absolute equality between the 
radiating power of the face and any other substance which could be used in the 
comparison, I think these results are quite near enough, especially when taken with 
those already tried, to prove that there is nothing special in the human organism, 
beyond the heat it radiates, to produce rotation of the cylinder. 
I attempted to verify the experiment of M. Thore’s in which he got reversed 
rotation by putting a hemicylinder behind the rotating cylinder. A half-cylinder of 
glass, 4^ inches across and 4f inches high, was put behind so that the suspended ivory 
cylinder was in the centre of the curve. The following experiments were then tried, 
the cylinder, as in the other cases, being of lampblacked ivory :— 
No. of 
experiment. 
Material of pillar. 
Maximum 
speed of one 
revolution. 
No. of 
revolutions. 
Exciting agent. 
48 
Polished ivory. 
seconds. 
18 
3 75 
Face. With glass cylinder 
49 
12 
4-5 
Face. W ithout glass 
50 
')') . 
1-25 
cylinder 
Hot water. With glass 
51 
18 
4’25 
cylinder 
Hot water. Without glass 
52 
Polished brass tube. 
0-5 
cylinder 
Face. With glass cylinder 
53 
?? 5 ? . 
19 
4-5 
Face. Without glass 
cylinder 
These results show that the effect of putting a half-cylinder as a screen behind the 
suspended cylinder does not produce exactly the effect described by M. Thore. It 
does, however, cause a marked diminution of action, and, had the cylinder and pillar 
been freely exposed to the air as in M. Thore’s experiment, reversal of movement 
might have taken place. I found it difficult to try accurate experiments in the free 
air of a room, owing to the interference of air-currents. The deadening of motion in 
my experiments, and its reversal in the experiments of M. Thore, I attribute to the 
reflection of heat rays from the concave surface of the cylinder, and their concen¬ 
tration to a focus on the further side of the suspended cylinder. 
The following experiments were made with the object of ascertaining what would 
really be the effect of an upward current of air on the suspended cylinder. A glass 
jet about 1 mm. in diameter was fixed vertically in front of the cylinder. To the jet 
Avas attached a long india-rubber tube, connected at the other end with a system of 
water-bottles in such a way that, by raising one of them, a gentle stream of air rose 
from the jet in front of the cylinder. The amount of air ascending could be varied 
at Avill from a scarcely perceptible current to a strong blast. A telescope was fixed 
near the bottles, some distance away from the cylinder, so that observations could be 
taken uninfluenced by the heat of the body. The blackened brass wedge, with its 
edge towards the cylinder, as in Expt. 43, was used as the pillar, and the lampblacked 
