150 
PROFESSOR OLIVER LODGE ON THE ABSENCE OF 
or paddles, would have a chance of success, unless there existed a trace of something 
akin to viscosity by which the medium could be got hold of, and as the previous 
arrangement of apparatus seemed as well calculated as any other to detect the 
existence of a trace of viscosity, whereby ether in the immediate neighbourhood of 
moving matter should sooner or later be more or less carried along by it, no funda¬ 
mental change in the mode of experiment seemed necessary ; only improvement in 
details, and some modifications, in order to secure a closer and a wider generalisation. 
Hitherto the experiments had been conducted with a pair of hard steel disks like 
circular saws, clamped together on a vertical axis, at a distance apart of one inch. 
These disks had been spun, at a speed not exceeding 1250 revolutions a minute in 
the most accurate experiments, and the effect of the motion on a bifurcated beam of 
light, whose two halves travelled in opposite directions several times round in the 
space between the disks, was observed. One half of the light travelled in the same 
sense as the motion, while the other half travelled in the opposite sense ; the two 
half beams were made to interfere in the field of view of a micrometer eye-piece, and 
a shift of the central band of the system by so much as the hundredth part of the 
width of a band could be observed. In making the above careful estimate of the 
result, however, the safe course was taken of assuming that gwfh of a band shift was 
the minimum certainly detectable. 
There were some modifications still to be fuade before accepting a definitely 
negative result of experiment. 
1st : to steady the motion, so that quantitative readings could be taken without 
tremor at a much higher speed of rotation. 
2nd : to continue the motion for some considerable time, and to narrow the light 
channel or watch the effect close to a disk. 
3rd : to increase the mass of the revolving matter. 
4th : to magnetise the revolving material. 
5th : to electrify it. 
The connexion looked for between ether and matter being something of the 
nature of viscosity, the space between the disks may be considered rather wide; 
though it is difficult to suppose that any motion generated at the surface of the disks 
in a substance possessing any of the properties of an ordinary fluid, should not spread 
into the nearly enclosed space between them. It may, however, be conceivably 
argued that this diffusion of motion might take considerable time, and hence the 
modification labelled No. 2 above wars called for. The modification No. 3 is to meet 
the argument that, even though a viscous connexion between ether and matter were 
disproved, it did not follow that there was not another mode of connexion com¬ 
petent to transmit motion from one to the other, viz. : the unknowm kind of 
connexion which is concerned in gravitation ; and to display any effect on this, 
a large mass must be used. 
