CASSKCK.MN KI.IU-rTOK WITH O >i;|;K(TU FII.I.H. C,:; 



lenses in respect to the paasji^'- of ;i ray through the instrument. Calculate from 

 the normal schemes, p. 58, for b= +'20, and ft = '01,0, +'01 respectively, the 

 value of // at each surface ami also at the focal plane F' 7 ; this will give the 

 necessary ajH-rtnn-s for complete inclusion of all rays I'mm the great mirror, up 

 to these, limits of ohli(|iiity. We find ax follows: 



Value of Semi-aperture. 



Hence if the great mirror is 40 inches in diameter, the reverser requires to be 

 16'2 inches, the first face of the corrector 12'2 inches, and the last face 12'6 inches; 

 the diameter of the image at the focal plane would be 10 '2 inches. 



It is necessary to verify that the corrector does not cut out any rays coming from 

 the great mirror to the reverser. By the data on p. 54, the first face of the 

 corrector is at a distance +'413750 beyond the surface of the great mirror. 

 Calculating the value of i/ along the ray y 1 = fiz' + b', for this value of x', where 

 b', ft are taken from the normal scheme for the ray Ixstween the surfaces O and O, 



we have 



Value of b. ft = - -01. P = '00. /8 = + -01. 



+ '200 +'154 +'159 +'163, 



+ '081 +'061 +'064 +'068. . . . (40) 



Thus the ray which just cleared the reverser on its way to the great mirror 

 would clear the corrector on its return. 



Allowing that '085 of the radius of the great mirror is unavailable the effective 

 aperture-ratio is reduced from 40/508'8 = 1 : 1272 to 36'28/508'8 = 1 : 14'05. 



The following table shows the inclinations of the ray to the axis of the telescope 

 between the various surfaces : 



