158 
PROFESSOR OLIVER LODGE ON THE ABSENCE OF 
just before stopping’, or sometimes a second or two after stopping’. When it was over, 
the bands were absolutely in the old place ; its effect had been to wave them about 
slowly and slightly. 
In all these experiments the brass collar coupling, with the copper wire force- 
tiansmitters, was used to connect the two axles, instead of the old friction clutch, 
which was insufficient and not so dependable. 
Possible Time Effect. 
On June G w'e kept the disks spinning for three hours at 1900 revolutions, to see if 
any shift developed with time. The result on this particular occasion w’as an apparent 
shift followed by a blur and invisibility of the fringes. They did not recover on 
stopping, but could be brought into visibility by moving some of the screws. This 
wais evidently a bad experiment, and the apparatus w'as overhauled and steadied up. 
Took another spin next day, at a speed of 2400 revolutions, for three hours, and not 
the slightest shift developed itself in this time. 
By June 23, the step bearing at the bottom of the axle shaft w’as replaced by a new 
one, and other inechaincal conditions were improved. The machine now ran up to 
2400 wdthout a tremor, and a current of 30 to 35 amperes was sufficient to do the 
driving. An observation w'as made with the drum in, with glazed wundows, no top or 
bottom (as before), the light going three times round, and the speed being kept at 
2100 for two hours. At the first instant there w^^s a shift of - 2 ^-th band, but it did 
not increase, nor did it recover on stopping. Went on with a reverse spin, also at 
2100, under the same conditions, and saw not a trace of shift at going or stopping, or 
during long spin—^only the usual flicker as the speed got very slowx The bands were 
distinct all the time. A good experiment. We conclude that time has nothing to do 
with the matter. 
Atiem'pt to Observe the Air Effect. 
From June to November, 1893, continual attempts w'ere made (except during a 
month’s vacation), by careful and repeated setting of the micrometer w'U’es on the 
bands, by taking the average of a set of readings at each speed and plotting them, to 
get some dependable record of the true air effect, free from disturbing causes. This 
labour was undertaken not only because it w'as thought of interest to observe this 
hitherto unobserved small quantity, but also because its detection w'ould emphasise 
the truly negative character bf the ether effect. 
Taking jx for air as 1’00029, the I' = 1 — y = "00058 6, and the fraction of a baud 
shift observed being a: at an angular speed w, and with n light-journeys round the 
optical square of side «, w^e should have Z’uwfr = 4 X lO^.r (see p. 772, loc. c?t.); 
wherefore, writing w = 'JttN, and considering that the observable a' is i^otli of a 
