Csoe:) 



XXV. On the Light of the Cassegrainian Telescope, compared with 

 that of the Gregorian. By Captain Henry Kater, Brigade- 

 Major. Communicated by the Right Hon. Sir Joseph Banks, 

 Bart. K.B,P.R.S. 



Read May 27, 1813. 



1 HE Cassegrainian telescope from its first invention to the 

 present time, has generally been considered to be merely the 

 Gregorian disguised, and to possess no other advantages over 

 it than the capability of being made shorter with the same 

 magnifying power. This opinion, joined to the inconvenience 

 of its inverting the object, has caused it to be thrown aside, 

 perhaps too hastily, and without a sufficient examination of its 

 properties. 



As the experiments which I am about to detail may possibly 

 lead to important conclusions, I shall perhaps be pardoned if 

 I relate the circumstances which induced me to engage in them. 



A self-taught artist of the name of Crickmore, who resides 

 at Ipswich, had by exclusive attention to the subject, brought 

 the Gregorian telescope to a degree of perfection surpassing 

 any thing of the kind I have ever yet met with. Some months 

 since, in the course of his experiments, he first completed a 

 Cassegrainian telescope of one foot in length, and on viewing 

 Jupiter with it, with a power of about 100, I was instantly 

 struck with the brightness of the image, far exceeding what 

 might have been expected from the aperture ; but I supposed 



