Capt, Kater’s Appendix to further Experiments 
diameter compared with the square of the diameter of the first 
circle, gave the ratio of the intensity of light at equal distances 
from the focus. 
Observers. 
Diameter of the Illu- 
minated circle 
the focus. 
Diameter of the cir- 
cle of equal illumi- 
nation without the 
focus. 
Ratio of the intensity 
of the light at equal 
distances from the 
focus. 
within. 
Without. 
A 
24 
17 
1000 
502 
B 
25 
17 
1000 
445 
K 
25 
17 
1000 
445 
C 
25 
18 
lOOO 
518 
Mean 
1000 
477.5 
I now caused a joint to be made in front of the board support- 
ing the mirror, which received the end of a light rod of wood 
about three feet in length. On this a thin board was contrived 
to slide easily at right angles, and the rod moving stiffly in 
the joint, could be set to any elevation so as to receive the 
light reflected from the mirror on the thin board. The board 
was covered with white paper divided by perpendicular lines 
at the distance of the tenth of an inch from each other. The 
observations were then made, and the ratio of the light deduced 
in the same manner as in the preceding experiments. 
