246 Capt. Kater's Appendix to further Experwie?its 
With disks of ground glass zvithin the foci. 
Distance of the furthest lamp 16 feet. 
Rays from the furthest lamp on the right 
hand disk. 
Rays from the furthest lamp on the left 
hand disk. 
Distance of the 
nearest lamp. 
Distance of 
the disks 
when equal- 
ly illumina- 
ted from the 
focus of the 
furthest 
lamp. 
Distance of 
the disks 
Vv'hen equal- 
ly illumina- 
ted from the 
focus of the 
nearest 
lamp. 
Intensity 
ofthelight 
within the 
focus of 
the fur^ 
thest lamp, 
that with- 
in the fo- 
cus of the 
nearest 
being 
1000. 
Distance of 
the disks 
when equal- 
ly illumina- 
ted from tlie 
focus of the 
furthest 
lamp. 
Distance of 
the disks 
when equal- 
ly illumina- 
ted from the 
focus of the 
nearest 
lamp. 
Intensity 
ofthelight 
within the 
focus of 
the fur- 
thestlamp, 
that with- 
in the fo- 
cus of the 
nearest 
being 
1000. 
Mean. 
4 
r> 
6 
7 
8 
3.38 
3>22 
3.30 
3,26 
3^19 
20,24 
1373 
10.53 
8,50 
^.99 
1231 
1124 
1151 
1117 
1 loS 
3.14 
3.23 
3 >i^' 
3^12 
2,98 
20,00 
1374 
10,39 
8,3^ 
6,88 
1089 
1129 
1084 
10.58 
998 
1 160 
1126 
1117 
1087 
1053 
From these last experiments, it should seem that a portion 
of the light forming the cone of rays from the nearest lamp 
is destroyed by the interference of the cone of rays from the 
furthest lamp ; but this is an inference too improbable to be 
received as conclusive without further experiments. 
The preceding method of determining the proportional in- 
tensity of light without the focus to that within, is not much 
to be relied upon, from the circumstance of the light after it 
has crossed at the focus appearing of a deeper yellozv colour thdin 
before, which renders it extremely difficult to decide when 
the disks are equally illuminated ; the circle of light, too, from 
the furthest lamp being very small so near the focus, and its 
illumination unequal in different parts, forms another source 
