Transcriber's Notes
Obvious typographical errors have been silently corrected. Variations in hyphenation and accents have been standardised but all other spelling and punctuation remains unchanged.
In caption of [Fig. 49].—Spherical Aberration of Concave Lens. Concave has been changed to Convex
In “[An objective of 4.56′ inches] aperture has a resolving constant of 1″ and to develop this should take a magnification of say 300,” 1″ has been hand altered in the original and may be 1′.
The table “[Characteristics of Optical Glasses]″ has been divided to fit within the width restriction.
The images corresponding to [Figs. 152] and 153 were reversed in the original. This has been corrected.