:\[ECHANICAL CONNEXION BETWEEN ETHER AND MATTER. 
159 
band, it follows nN must be 800, in order to show the air effect, that is, the speed 
must'rise to 6000 revolutions a minute with a light-journey of three times round. 
This speed would lead impractically near to the bursting-strength of materials; but it 
was hoped that, by taking the average of a series of settings, f of a band could 
be safely observed, and thus the effect of the air-spin detected. And if everything 
had gone well, I think this might have been done, but the difficulties met with 
caused a careful examination of the brick pillars and foundations beneath the floor, with 
the result of discovering that the brick pillars, bj^ which the optical frame was ulti¬ 
mately supported on its gallows support (fig. 11, p. 767, ‘Phil. Trans.,’ 1893), were 
not so entirely independent of the whirling machine’s stone altar as they ought to 
have been. During the vacation bricklayers and carpenters were accordingly called 
in to re-set the warped pillars beneath the floor, and to clear away all joists and every¬ 
thing that could be suspected of in any way helping to transmit vibration. The 
result of this work was a beautiful steadiness and visibility 
at high speeds; but still the bands showed what we call a 
concertina action, that is, a slio-ht movino’ of the lateral 
hands in or out from the central one, as the speed varied. 
There would be no strong objection to such motioir, if the 
precise symmetry of the central band could be assured, 
but, as this assurance was not forthcoming, the central band 
sometimes shared in this motion ; and even if it did not, its 
steadiness was suspicious, because perhaps it ou(jht to have 
slightly moved. 
The residual trouble appeared possibly due to an obscure 
influence on the glass windows of the drum, possibly a slight 
warping due to warmth or air pressure, and an attempt was 
made to dispense with the window panes and to screen 
from the blast by another method. Accordingly a fresh 
drum was made of brass, with a pair of deflecting rims or 
flanges, so placed as to catch the air whirled off the disks 
all round, and deflect it out of the way upwards and down¬ 
wards, the light passing on through a chink or slit in the 
brass drum to the region protected by these flanges (fig. 4). 
Some residual draimht did however manao-e to reach the 
O O 
mirrors, and, although they were strongly supported, it seemed to flutter them even 
if unable regularly to tilt them. It was then attempted to lessen the freedom of air 
supply to the axis of rotation, by wooden circular boards, fitting the axle loosely, and 
nearly as large as the drum, thus greatly interfering with the supply of air. As soon 
however as the ventilation was thus interfered with the air got distinctly hot, which 
was a worse evil. 
The drum was supported separately on long wooden girders, so that no part of it 
