“ NEW FORCE ” OF M. J. THORE. 
459 
ivory was used as the cylinder. The jet was half an inch from the cylinder, and a 
moderate stream of air issued from it. The cylinder revolved three times to the right 
and then two and a-half to the left. 
Similar experiments were tried, placing the jet at different distances from the 
cylinder, altering the velocity of the air, and increasing the size of the orifice, but the 
results in all cases were of the same kind ; the cylinder first rotating once or twice to 
the right, and then about the same amount to the left. No permanent movement of 
eight or ten revolutions could be got, neither by airy modification of the draught could 
I see my way to produce any of the strong rotations easily obtained with hot bodies. 
There is a general accord between these experiments, but the agreement between 
repetitions of the same individual experiment is not so close as I should like. All 
were performed in duplicate or triplicate, and the mean taken. Much of the 
discrepancy may be accounted for by great variations of zero owing to the silk fibre 
becoming warmed or absorbing moisture, and part may be due to the impossibility of 
bringing the pillar and cylinder exactly 1 mm. apart in every case. 
Another noteworthy point is the non-accord between the maximum speed of one 
revolution and the total number of revolutions performed by the cylinder. 
All the experiments tried so far show that the rotations are produced by radiant 
energy falling on the cylinder and pillar. Radiant heat (and in less degree light) 
falling on the lampblacked surfaces is absorbed, and increases the surface-temperature. 
There are two ways in which this increase of temperature may act :— 
1. It may produce a current of warm air, rising in front of the surfaces of the 
moving body; to replace this, cold air will come in from all sides, and, striking against 
the delicately suspended cylinder, caused it to rotate. If, however, the source of heat 
is of considerable surface, such as the face, or a Winchester quart-bottle full of warm 
water, it is difficult to imagine that there would be much tendency to rotate in one 
direction rather than in the other. 
2. An increased surface-temperature of the cylinder and pillar may produce an 
increase of molecular pressure between the two bodies, and thus give rise to motion, 
after the manner of the radiometer. In this, as in the former case, the movement 
should be in the opposite direction to what it is in reality, as it would be produced by 
mutual repulsion acting between the sides nearest the source of heat. 
It seemed likely that information decisive as regards one or other of these two 
theories might be gained by suspending the cylinder in a glass tube attached to a 
Sprengel pump, and taking observations at different degrees of exhaustion. An 
apparatus was accordingly fitted up as shown in the accompanying figure (fig. 4). 
ABC is a glass tube, 39 inches long, expanded into a bulb, BC, at the lower end, 
and connected with a Sprengel pump at the upper part. An ivory cylinder, D, is 
suspended from A by a single fibre of cocoon silk, and at E is attached to the glass 
bulb a hollow brass tube, inside which, but not touching it, is a platinum spiral with 
the two ends sealed through the glass. By making battery contact between the 
3 N 2 
