of the Cassegrainian Telescope, &c. 
233 
The magnifying powers being 157 in the Cassegrainian 
telescope and 125 in the Gregorian, their comparative light 
when reduced to the same aperture and power will be as 
to or as 678 to 290. 
It may perhaps be desirable to place the results of the three 
experiments in one point of view. Thus, calling the light of 
the Gregorian telescope in every instance 100, we have the 
light of a telescope of the Cassegrainian form of equal power 
and aperture, by the first experiment 235, by the second 148, 
and by the third 234. 
The surprising agreement of the first and third experiments 
with each other, excites an inquiry as to the cause of the dif- 
ference observable in the second, as equal care and attention 
were bestowed on all. 
The Cassegrainian telescope used on that occasion I have 
been unable to procure again, but from the inquiries I have 
since made, there is some reason to believe that, in addition to 
the polish of the specula having been somewhat impaired, as 
lemarked in my last paper, its convex mirror was too small 
to receive the whole cone of rays, and to this circumstance 
principally I am inclined to attribute the deficiency of light in 
the second experiment when compared with the first and third. 
If the mean of all three experiments be taken, the relative 
quantity of light will be as 20^ to 10 ; but, if the second ex- 
periment be rejected, and the mean of the first and third be 
considered as correct, the light will be very nearly as 23I- to 
10 in favour of a telescope of the Cassegrainian form compared 
with one of the Gregorian construction. 
Ipswich, 1 6th July, 1813 
MDCCCXIV. 
I have the honour to remain, &c. &c. 
H h 
HENRY KATER, 
