340 
Transactions of the Society. 
side of the Microscope, to study the chain of proof of this fundamental 
formula from “ Snell’s law of sines,” “ refraction through a prism,’ ’ 
and “refraction through a thin lens,” which are given in most 
text-books of physical science. 
Table of Penetration. 
Data. — Vision emmetropic, W = 250 mm. ; S = ‘127 hid-. 
Balsam mounted objects, /a = 
= 1-5. 
Penetration. 
Formulae. 
Power. 
Aperture. 
Visual. 
Photogriphic. 
(visual) 
10 
mm. 
nnn. 
1 
•75G 
* 7G 
(iii.) 
20 
•2 
•283 
•19 
1 
50 
•3 
•1 
•051 
(iv.) | 
f 
100 
•3 
•025 
•025 
150 
•5 
•01 
•01 
200 
•5 
0035 
•007 
(v.) 
250 
•5 
•003 
■006 
250 
•95 
•0016 
•t 032 
1 
300 
•95 
•0013 
•0026 
300 + 
— 
now inappreciable. 
— 
(photographic) 
(iv.) 
— 
— 
— 
— 
Fig. 41. 
