MECHANICAL CONNEXION BETWEEN ETHER AND MATTER. 
151 
Probably the mass necessary to demonstrate any action of the gravitational kind 
would be impractically large, unless the earth itself could be used. Now, by staking 
out mirrors at the corners of a field, it is arithmetically quite possible to arrange 
for a perceptible shift of the bands due to the rotation of the earth, if it carries ether 
round with it ; but it does not seem possible to experimentally observe that shift, 
unless some method could be devised of making the observer and his apparatus 
independent of the rotation. 
It is to be observed, that since a motion of the disks relatively to the observer 
and the light causes no effect, the ether being stationary, it follows that a motion of 
the light and observer would produce an effect, since they would be moving 
relatively to the ether. Hence if, instead of spinning only the disks, the whole 
apparatus, lantern, optical frame, telescope, observer and all were mounted on a turn¬ 
table and caused to rotate, a reversible shift of the bands should be seen. It would 
not matter in the least whether the disks were revolving or not, and they might just 
as well be absent. The effect would be of an aberrational kind, the opposite light 
beams being accelerated and retarded by the motion appropriately. In an actual 
experiment of this kind, centrifugal force would give some trouble by introducing 
strains, and rapid rotation would be uncomfortable for the observer ; but really rapid 
rotation should be unnecessary to show the effect. My present optical apparatus 
mounted on a turn-table revolving 4 times a minute should show something, viz. : 
y^oth band shift each way. A certain amount of discomfort during the accelerative 
stages of any speed could hardly be avoided, and even during steady motion there 
would be some inconvenience ; for instance, at 30 revolutions a minute the observer’s 
weight, at a metre and a half from the centre, would be half as much again, and 
would be inclined at 45° to the vertical. This, however, might be tolerated. 
If the ether is stationary near the earth, that is, if it be neither carried round nor 
along by that body, then a single interference square, 1 kilometre in the side, would 
show a shift of rather more than one band wfidth, due to the earth’s rotation in these 
latitudes ; see p. 772, ‘ Phil. Trans.,’ 1893. But as the effect depends on the area 
of the square, a size of frame capable of mechanical inversion is altogether too small; 
there may, however, be some indirect ingenious way of virtually accomplishing a 
reversal of rotation—something for instance based on an interchange of source and 
eye—and if so, it would constitute the easiest plan of examining into the question 
of terrestrial ether drift. 
It matter conceivably drags the ether with it in proportion to its mass, an ordinary 
lump of matter can hardly be expected to cope with the heart and to shift it in 
opposition to that body ; nevertheless, since nothing is known on the subject one 
way or the other, it was thought well to give a more massive body a chance, by 
rotating a solid piece of iron about three-quarters of a ton in weight, and with 
a much narrower groove or channel cut in it for the passage of the light. It was 
easy to arrange at the same time for the magnetisation of this piece of iron when 
