232 Capt, Kater’s further Experiments on the Light 
sively cut out till a card appeared decidedly brighter when 
viewed through the Cassegrainian than through the Grego- 
rian. 
The following measures were then taken. 
Cassegrainian Telescope. 
Diameter of the circular 
opening in the paste- 
board 
Diameter of the back of 
the small mirror 
Length of the arm 
Thickness of ditto 
Inch. 
Gregorian Telescope. 
3,600 
l,.QOO 
0,830 
0,225 
Diameter of the large 
mirror 
Diameter of the back of 
the small mirror 
Length of the arm 
Thickness of ditto 
Length of a bar contain- 
ing the adjustment 
Its width 
Diameter of three semi- 
circles used as rests 
for the great mirror 
Inch. 
smo 
1,230 
L155 
0,175 
0,700 
0,150 
0,375 
From the above data the following calculations were made. 
Area of the circular inch, 
opening in the paste- 
board - 10,179 
Area of the back 
of the small 
mirror to be 
deducted - 2,836 
Area of the arm 
to be deducted 0,191 
3,027 
Area of the large mir- inch. 
I'or - _ 12,254 
Area of the back of the 
small mirror to be 
deducted - 1,188 
Area of the arm 
to be deducted 0,202 
Area of the bar 
containing the 
adjustment to 
be deducted 0,105 
Area of the three 
semicircles to 
be deducted 0,166 
1,661 
Area of the portion of 
the mirror exposed 
to the light - 7,7^2 
Area of the portion of 
the mirror exposed to 
the light - 10,593 
