244 ? Capt. Kater's Appendix to further Experiments 
f. The focus of the furthest lamp. 
F, The focus of the nearest lamp. 
d, The distance of the disks from the focus of -the furthest 
lamp^\vhen equally illuminated. 
D, The distance of the disks from the focus of the nearest 
lamp when equally illuminated. 
Then the relative intensity of the light at equal distances on 
each side of the focus will be ^ 
Lxrf 
-- 
/xD 
With disks of card paper. Distance of the furthest lamp 
16 feet. 
Ra)s Irom the furthest lamp on the right 
hand disk 
Rays from the furthest lamp on 
the left ‘.and disk. 
Distance 
of the 
nearest 
lamp 
Distance of disks 
from the focus when 
equally illuminated. 
Intensity of 
light without 
the focus, that 
within being 
1000, 
Distance of disks 
from the focus when 
equally illuminated. 
Intensity of 
light without 
rhe focus, that 
within being 
I coo. 
Without. 
Within. 
Without. 
Within. 
5 
6 
7 
D 74 
D 47 
1,14 
8.77 
5 . 7*5 
4,10 
804 
7*>3 
587 
D 7.5 
D 57 
1 ,32 
8,7b 
5 bb 
3 >92 
815 
901 
857 
The mean of these experiments gives the intensity of light 
within the focus to that without, as looo : 788. 
Disks of glass ground on both sides were now substituted 
for those of card paper, and v\ ith these the following experi- 
ments were made with the utmost care. 
