165 
The President’s Address. By E. M. Nelson. 
~^Sw- •*»> 
g = -= ' 255 ; (/j. - \)g = ' 1321 ; - < 7 ?- = - '1053 ; 
A 1 
— gs= *1053; rs = — *1706; 
s — r + (/x — 1) £/ = — * 6939 = h • 
(/i- l)h= - *3594 =k; p = ^j^= - 1517 ; 
2 = ~f~ = ~ '1517 ; /='-£=• 4747 . 
<Z = -0844 ; elf = -04006 ; /"/= - -6026 ; 
/"+ f — d = — 1-0687; 
Q = 1- JTT 
df _ *04006 n- AQ _. Q 
/" + / - d _ ? _ “F0687 “ ? + 03748 ; 
</> 
/"/ _ - *6926 
f'+f-d - 1-0687 
= -6481. 
D = -01692 ; Df = - -06846 ; </>/'=- '9456 
<£ +/' - D = - -8578 ; 
F 
= 1 - 102 . 
Working distance = distance of the focal point from last surface 
of lens = * 887. 
Magnifying power ^ — 1 = 8 * 07. 
We see that the first principal point p" is * 1353 distant from the 
vertex of r”, it is positive and therefore it is measured towards the 
right hand; the second principal point a" is *0673, also measured 
1898 * ' N 
