on the Light of the Cassegrainian Telescope, &c, 245 
With disks of ground glass. Distance of the furthest lamp 
16 feet. 
Rays from the furthest hmp on the right 
hand disk. 
Rays from the furthest lamp on the 
left hand 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 fo' us when 
1 equally illumiiiated. 
i _ 
Intensity of 
I'ght withoui 
rhe focus, that 
w’thin being 
1000. 
Without. 
Witiiin. 
1 
i W'lthout 
Within. 
4 
5 
■ 6 
/ 
2.58 
1,80 
1 , 3 'o 
1 ,16 
14,28 
8,71 
5.87 
4 08 
1 
1441 
872 
629 
614 
D 71 
1,52 
T 34 
1 . 5, ‘5 
8.99 
5.89 
4.07 
563 
384 
606 
6*27 
From these experiments, the intensity of light within the 
focus to that without appears to be, as 1000 : 742; but as the 
first experiment is evidently erroneous, if it be rejected, the 
intensity of the light within the focus to that without, will be 
as 1000 : 655. 
The difference of these results from those obtained by the 
methods detailed in the former part of this paper, led me to 
examine the intensity of the light of both cones of rays zvithin 
the foci. For this purpose, the following experiments were 
made. 
