The Penetrating Power of the Microscope. By E. M. Nelson. 341 
* Proof that v = • 
w 
1 1 _ I. 
V V f 
«’+/ + f+/ / 5 
w v 
p' = w+f ; p = v-\-f\ 
(w + /) (y + /) = (w -f v + 2/)/; 
Proof that / = — 
' M 
i ~ image, o = object. 
D = p' +/; 
1 _ i _ 1 . - pp 
f p p ’ p' - p ’ 
/(p' -p) =pp'; 
/p' = (p' + /) p ; 
, P'+/^ d 
J f M ’ 
p 
The above figures illustrate the formula on page 181 ante. 
* First demonstrated by Sir Isaac Newton. 
Erratum . — Page 336, line 5 from bottom, for “(In the absence of all knowledge 
of the well-known formula, / = — the proof is given infra)" read “(In the absence 
d 
of all knowledge of the well-known formula, m — j , Bee p. 182 (ii.), the proof is 
given infra.)" 
