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March 8, 1876. 
THE PRESIDENT (PROFESSOR CLERK MAXWELL) in the Chair. 
The following communications were made to the Society : 
(t) On the Friction attributed to the Ether. 
By Mr W. M. Hicks. 
In the Proc. Roy. Soc. Vols. XIV. XV. XXI. appear descrip- 
tions of some experiments of Stewart and Tait on the heating 
of a disk by rapid rotation in vacuo. The experiments were 
made with thin disks of aluminium and ebonite, the apparatus 
with a thermo-pile being placed inside a receiver and the 
receiver exhausted. On rotating the disk for 30” or 40” the 
pile showed a heating effect. 
For aluminium disks of 2 in thickness the effect on the 
pile corresponded to a rise of temperature of about -85° F. and 
of #7, in thickness to a rise of 1°7° F. 
They showed that the heating effect is not due to either 
1. Rotation under the Harth’s magnetic force, 
2. Nor conduction of heat from the bearings, 
3. Nor to radiation or convection from the wheel-work, 
4, Nor to vibrations of the disk. 
In a second series of experiments, they found that the heat- 
ing effect was due to two causes, 
1. A residual gas effect, 
2. An unknown effect. 
- This unknown effect they set down as due to etherial fric- 
tion, but they arrive at this conclusion by a process of exhaus- 
tion, and hence they cannot be sure of having exhausted all 
other possible causes. And one cause, at least possible a priori, 
they do seem to have passed over. 
