PLATE I. 



Optics of the Compound Microscope. 1 



Fi Upper focal plane of objective. F 2 Lower focal plane of eyepiece. 



A Optical tube length = distance between Fi and F 2 . 



Oi Object. 2 Real image in F 2 transposed by collective lens. 



03 Real image in eyepiece diaphragm. 



4 Virtual image formed at the projection distance C, 250 mm. from EP. 

 EP Eye-point. CD Condenser diaphragm. L Mechanical tube length 



(160 mm.). 

 1, 2, 3 Three pencils of parallel light coming from different points of a distant 

 illuminant. 



1 From " The Microscopy of Drinking Water " by George C. Whipple. Reproduced through the 

 courtesy of the author and that of the Bausch & Lorab Optical Co. 



Frontispiece 



