776 
DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
X-wire. 
Vertical wire. 
(Set and reset in yellow 
(Set and reset in centre 1 
of first band.) 
of middle band.) j 
r 
811 
20 
801 
20 
Disks stationary 
84 
21 
91 
21 
8.3 
22 i 
90 
20i 
85 
L 
Average 85 
Average 20-^ 
The width of this average band was 208|- divisions. 
Hence when stationary the error of setting of the vertical wjre each time did not 
attain too^^ ^ band ; and the probable error of the average of a series of settings 
is very small. 
Same operation continued, with disks spinning. 
Disks revolving 1260 times 
a minute. (Bands now 
not so clear. There was 
too much tremor) 
Average 
X-wire. 
Vertical wire. 
85 
26 
90 
30 
95 
32 
89 
34 
89 
26 
90 
26 
85 
27 
89 
29 
The width of this average band was 221 divisions. 
Here the error of individual settings of the important wire amounts to -^th of a 
band in one case, and the probable error is, say, - 7 -oth. The error in the average of a 
series, however, would be less than y^ol^h, even under the above disadvantageous 
circumstances. 
(The average shift caused by this spin was 8‘5 divisions, or, say. = a^th of a 
band.) 
The effect of the tremor of the whiiling machine on the optical part was becoming 
too conspicuous, and accordingly all the saw cuts and separations between drum and 
frame had to be examined. A slight contact was discovered. 
46. On the 19th March a rather hasty pair of spins were taken, with tlm following 
results:— 
