W. Crookes—Radiant Matter. 253 
ever pole is made negative the stream of Radiant Matter darts 
8. | 
from it along the tube, and striking the apne vanes of the 
little paddle-wheel causes it to turn round and travel along the 
railway. By reversing the poles I can arrest the wheel and 
send it the reverse way, and if I gently incline the tube the 
force of impact is observed to be sufficient even to drive the 
wheel up-hill. 
This experiment therefore shows that the molecular stream 
from the negative pole is able to move any light object in front 
it 
OT 1t. 
The molecules being driven violently from the pole there 
should be a recoil of the pole from the molecules, and by 
arranging an apparatus so as to have the negative pole mova 
ble and the body receiving the impact of the Radiant Matter 
xed, this recoil can be rendered sensible. In appearance the 
apparatus (fig. 9) is not unlike an ordinary radiometer with 
aluminium disks for vanes, each disk coated on one side with 
a film of mica. The fly is supported by a hard steel instead of 
glass cup, and the needle point on which it works is connected 
by means of a wire with a platinum terminal sealed into the 
glass. At the top of the radiometer bulb a second terminal is 
sealed in. The radiometer therefore can be connected with an 
induction-coil, the movable fly being made the negative pole. 
For these mechanical effects the exhaustion need not be 
80 high as when phosphorescence is produced. The best pres- 
sure for this electrical radiometer is a little beyond that at 
which the dark space round the negative pole extends to the 
