Optics of the Compound Microscope.^ 
Fi Upper focal plane of objective. F2 Lower focal plane of eyepiece. 
A Optical tube length = distance between Fi and F2. 
Oi Object. O2 Real image in F2 transposed by collective lens. 
O3 Real image in eyepiece diaphragm. 
O4 Virtual image formed at the projection distance C, 250 mm. from EP. 
EP Eye-point. CD Condenser diaphragm. L Mechanical tube length 
(160 mm.). 
I, 2, 3 Three pencils of parallel light coming from different points of a distant 
illuminant. 
> From “The Microscopy of Drinking Water” by George C. Whipple, 
courtesy of the author and that of the Bausch & Lorab Optical Co. 
Reproduced through the 
Frontispiece 
