9 8 Mr t RAMSDEN on a new Con dm Si i on 
from the eye. The difpofition above delcribed will be found 
conformable to that idea. 
Let AB (fig. 4.) reprefent an image formed by the object - 
glafs of a telefcope, V the firfl eye gl a is, as already defcribed, 
with its plane fide towards the image ; let AC be the axis of a 
pencil of rays incident on the firft lurface of the lens V, and Ae 
an extreme ray of the fame pencil. Take CF toCA as the fine of 
incidence out of air into glafs is to the fine of refraction, 
and F will be the focus of this pencil after paffing through 
the firft furface of the lens V. From the point F draw the 
angle CFa, the incident pencil on the fecond furface of this- 
lens, continue the lines FC and Ft 5 to b and r refpeCtively, and 
draw the perpendiculars O I and OK on the point C, defcribe the 
arc nd , and making cd to ab , as the fine of refraction out of 
glafs into air is to the fine of incidence, draw cd continued till 
it cuts the axis in P. In like manner, on a center e defcribe 
the arc mg, and making yg to or as the fine of the angle of re- 
fraction is to that of incidence, draw the line eg Qj continue it 
and the line C d backward till they meet each other in b, and it 
will be the focus of the emergent pencil from the fecond fur- 
face of the lens V. On the axis CF fet off the diftance C ds 
equal to C h, and draw es and Ce. Now it is evident from the 
figure, that the focus of the emergent pencil will be nearer to 
C than the objeCt itfelf, in the proportion the angle Cse 
exceeds the angle C±\e. 
Thus, from the great angle of incidence of the oblique pen- 
cil on the fecond furface of the lens, the focus of the emergent 
pencil is brought nearer to P the fecond eye- glafs, while that 
of the principal pencil remains the fame, or very nearly fo ; 
and the image will become more diftinCt towards the edge of 
the field the nearer P h and PT approach to equality. 
7 
To 
