822 SUMMARY OF CURRENT RESEARCHES RELATING TO 



dation, therefore, should be as large as possible, so that the image might 

 form as near as possible to the eye. If, on the other hand, d^ > /, 

 1 — d^F is negative, and to augment the amplifying power L' must 

 diminish, i. e. I', the distance of accommodation, must be as large as 

 possible. The most advantageous case is that of a hyperpresbytic eye, 

 in which case L' is negative. For the Microscope the conditions are 

 inverse. 



(6) Comparative amplifying power corresponding to the case in 

 which I' = I, i. e. the image is compared with the object supposed to be 

 placed at the same distance from the eye. 



In this case we have 



r, = G. 



(c) Absolute amplifying power, which represents the proper action 

 of the instrument supposing the object placed at the same distance from 

 the eye assisted by the instrument as from the naked eye. 



We have 



1= do+f- q, 



where q is the distance F Q, 



Substituting in formula (3) we have 



= l + d,FCl-d,L') (9) 



on replacing G and q' by their values q' F and I' + f — d^ respectively. 

 Where the principal space e cannot be neglected, 



l = do+f-q-\-e, 



and the formula becomes 



r„ = l + c^„F(l - d,-L') -^ eVr. 



When either the relative or absolute amplifying power is known, the 

 other can be determined by the connecting formula 



r„ = r, X I (10) 



For the simple lens, Microscope, or ophthalmoscope the consideration 

 of the relative is of more importance than that of the absolute amplifying 

 power ; but for telescopes or spectacles, in the use of which we are not 

 free to modify the distance of the object from the eye, the absolute 

 amplifying power alone can be used. 



For the case of the astronomical telescope, where the dioptric power 

 is zero, M. Monoyer * has given the formula 



F, r^ . 1 + (d, + d,) F. -| r 



F; 



Comptes Eendue, June 18th, 1883. 



^_^(l-d,F,)L'-\ (11) 



