Brigade'^ Major Kater on the Light, &c. ' 207 



this to have been a deception arising from the specula being 

 more exquisitely figured than usual, which, producing greater 

 distinctness, occasioned the idea of superior light. A short 

 time after this, the same artist received an order for another 

 telescope, which, from the success that had attended his recent 

 efforts, he recommended to be of the Cassegrainian form. 

 The aperture was five inches, the length thirty inches, and 

 with a power of near 400 the image was so perfectly dis- 

 tinct and luminous, that I could no longer hesitate to conclude 

 that, from some unknown cause, the Cassegrainian telescope 

 actually possessed far more light than the Gregorian, and I 

 waited most anxiously for an opportunity of verifying this, and 

 determining the difference by experiment. 



Such an opportunity soon presented itself, and under cir- 

 cumstances peculiarly favourable, as another excellent tele- 

 scops of the Cassegrainian form was made, and I was fortu- 

 nate enough to procure a Gregorian made by Mr. Crickmore 

 some time before. The mirrors of both these telescopes were 

 cast at the same lime, and from the same pattern, so that no 

 difference of light could arise from any difference in the com- 

 position of the metal. The magnifying power of both instru- 

 ments was ascertained by experiment to be very nearly equal ; 

 but thfe excess was rather on the side of the Cassegrainian. 



The telescopes being placed side by side, were directed to a 

 printed card, at the distance of fifty yards; and on viewing it, 

 the far superior brightness of the image in the Cassegrainian 

 was strikingly apparent. Having prepared a circular piece of 

 paste-board to close the end of the Cassegrainian telescope, 

 I drew a number of concentric circles on it, at the distance of 

 the twentieth of an inch from each other. The paste-board 



