C 231 ;] 
XIII. Further Experiments on the Light of the Cassegrainian 
Telescope compared with that of the Gregorian. By Captain 
Henry Kater, Brigade Major. In a Letter addressed to the 
Right Hon. Sir Joseph Banks, Bart. K. B. P. R. S. 
Read November 18, 1813. 
Sir, 
Since you did me the honour of submitting to the Royal 
Society my experiments on the comparative light of the Cas- 
segrainian and Gregorian telescopes, I have been so for { unate 
as to have an opportunity of establishing the conclusions de- 
duced from them by another experiment, the detail of which* 
I trust will not prove unacceptable. 
The telescopes used on the present occasion were the ex- 
cellent Gregorian described in my former paper, and a new 
Cassegrainian constructed by Mr. Crickmore. The diameter 
of the large speculum of this instrument is 4,9 inches, the 
distance between the mirrors only 18 inches, and it bears a 
power of about 550 (as roughly determined by experiment) 
with perfect distinctness and considerable light. 
The magnifying powers used were 157 in the Cassegrainian, 
and 125 in the Gregorian; these were carefully determined 
by experiment, A circular piece of pasteboard was then pre- 
pared to close the end of the Cassegrainian telescoj^e, and 
concentric circles were drawn on it at the distance of the 
twentieth of an inch from each other. These were succes- 
