172 



though the little mirror were formed truly elliptical, it 

 vvould not make each of these pencils converge again 

 (at the place of the second image, formed behind the 

 first eye-glass) to single points, but to another series of 

 points; by which the rays of contiguous pencils would 

 be blended with one another, and make the object which 

 is viewed, by means of these pencils, so transmitted to 

 the eye, and, by it, refracted to a third series of points, 

 jiear the retina, at the bottom of the eye, appear hazy 

 and indistinct. 



These remarks will be applied to our present purpose^ 

 by considering: 



First. That the rays, reflected by the several annuli, 

 in the surface of the great mirror, will fall on the an- 

 nuli of the same order, in the little mirror; the rays from 

 the outer, inner, or intermediate annuli of the one, pro- 

 ceeding to the like annuli in the other. 



Secondly. That the farther the focus, or point of con- 

 vergence, of any annulus of the great mirror, is distant 

 from that mirror, the nearer will be the point of di- 

 vergence of this part of the whole pencil, (among the 

 series of such points), to the little mirror. Also, that 

 the interval, between any one point in the series and this 

 mirror, cannot be altered, by moving the mirror, without al- 

 tering the intervals of all the rest; which, after the telescope 

 is brought to the distinctest vision, cannot be peraiitted. 

 Thirdly. That, if the focus of any annulus, of the great 

 mirror, be farther from it, thai> those of the other an- 

 nuli, 



