Capt. Kater's Appendix to further Experiments 
With small Transparent Disks. 
Distance of the candle from the mirror iS6 inches. 
Ratio of the inten- 
Distance of the disks when 
Distance 
Distance 
sity of the light at 
Observers 
equally illuminated. 
of the disk 
of the disk 
equal distances from 
from the 
irom the 
the focus. 
focus 
focus 
witbout. 
within. 
1st reading. 
ad reading. 
mean. 
Within. 
Without. 
w 
23^85 
26,50 
2347 
10,26 
14.91 
1000 
474 
K 
25,20 
25,65 
2542 
10,26 
15,16 
1000 
458 
Myself 
25-37 
2543 
2540 
10,26 
15.14 
1000 
459 
Mean 
1000 
463.7 
If the mean results of the various experiments be now col 
lected they will appear as follows : 
ist set. By the diameters of the circles of 
illumination - - _ 
sd — By ditto - - - 
3d — By white circles on black cards 
4th — By large transparent disks 
3th — By disks of card paper on wires 
6‘ih — By Plaister of Paris balls 
7th — By small transparent disks 
Mean 
1000 
477.5 
1000 
42 J ,6 
1000 
43 
1000 
43I1O 
1000 
44^’5 
1000 
451.1 
1000 
463.7 
1000 
449.2 
The following method, by which both disks may be seen 
at the same instant, was suggested by a friend. 
"I wo lamps were procured, and the wicks being trimmed so 
that the flames appeared of an equal size, one lamp was 
placed 16 feet from the mirror, and the other 4 feet, which 
