DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
777 
First, with direction helping the reflected beam. 
X-wire, 
Vertical wire. 
At rest. 
13 
78 
(\ = 109) 
1220 revolutions . 
5 
80 
(\ = 163) 
At rest. 
K 
0 
81 
(A = 164) 
Reversed the brushes, and took a spin in the opposite direction,. 
Second, direction helping the transmitted beam. 
X-wire. 
Vertical wire. 
At rest. 
13 
81 
(A = 172) 
1220 revolutions . 
7 
85 
(A = 170) 
At rest. 
' ■■ ■ 
Something happened that prevented the last readings from being taken. Notice 
that the yellow band seemed to have slowly returned to its old position in the 
interval between the two spins. These slow recoveries are frequent. Here the 
wave-length, or width of band, corresponded to 169 divisions at first, and the first 
shift was only two divisions ; but the shift was spurious, for instead of returning, it 
went on, or at least stood still. The small shift (4 divisions) in the same direction 
observed on reversal was also no doubt spurious. I feel sure that I have never 
observed a genuine reversible shift of the middle band due to rotation. 
Now the light was going three times round the frame, and if the ether bad been 
carried round full speed with the disk there would have been a shift of 3^ bands, or 
550 divisions at each rotation, or over 1000 divisions in all, whereas not more than 
two divisions at the outside were seen, and they might readily be spurious. 
In saying they were spurious, I mean not that a shift so small as this could not be 
observed, but that th'ere was amply sufficient tremor to account for it 
The entire absence of perceptible shift at about 800 revolutions, before any 
important tremor has occurred, is to me really the most conclusive fact ; and I feel 
confident that either the ether between the disks is quite unaffected by their motion, 
or, if affected at all, that it is by something less than the thousandth part. At the 
same time, so far as rigorous proof is concerned, I should prefer to assert that the 
VELOCITY OF LIGHT BETWEEN TWO STEEL PLATES MOVING TOGETHER IN THEIR OWN 
PLANE AN INCH APART IS NOT INCREASED OR DIMINISHED BY SO MUCH AS ^oTH 
PART OF THEIR VELOCITY. 
5 G 
MDCCCXCIII.—A. 
