162 
PROFESSOR OLIVER LODGE OX THE ABSENCE OF 
(To realize that such readings fail to show the air effect it may be simplest to 
write down ideal readings that would show it exactly, viz. :— 
each division being -troth X 
J? r 
9 • 5 
9 9 : ? 
9 9 9 9 
Or the following would do equally well, though less obviously :— 
94-4 
94- 6 
94*4 
95- 2 
94-4 
where there is an irreversible shift of half a division (x 2 o superposed upon the 
reversible effect.) 
After the overhauling of the foundations, in September, the bands were beautifully 
distinct, and there was no tremor. There was now no clearly perceptible shift of 
the middle band, but still there was a concertina action, shown by a broadening of 
the bands during spin, thus altering the scale of wave-length. The following 
extract will serve to illustrate this 
8tli September. 
IFitb the Disks at rest, the middle 
hand read. 
7 while the yellow of the first hand read 
85 divisions 
With the Disks spinning 3000 I’evs., 
the middle hand read .... 
7 
107 
With the Disks at rest, the middle 
band read . 
7 
85 
With the motion reversed 3000 revs., 
the middle hand read .... 
7 
102 
AVith the Disks at rest, the middle 
hand read. 
7 
85 
Here the constancy of the number 7 means that no change could, be seen, but the 
readings are not averages, nor was the wire reset, and nothing less than a whole 
division shift would have been observed. The air effect would require a division 
shift. The existence of the concertina effect was held to render useless an attempt 
to take a serious set of averages ; and by no means could it be wholly got rid of. 
Ultimately we decided to do away with the optical frame so close to the disks 
altogether, and to arrange the mirrors at a distance, out of the blast, on brackets 
94-4 
94-1 
94-4 
94-7 
94-4 
if they had been obtained. 
