National Geographic : 1920 Feb
"sthroh t a se When the Halves of the Conning-Tower Meet. Read the Range -and FIRE 1 Do you know how our gunners find the range or distance of an enemy target-a submarine far off in gray wastes of sea, or an enemy post on a distant hillside? They train a range-finder" on it, turn a screw till the halves of the image meet, and read the distance in yards or meters directly from a scale. It is a matter of seconds only. Through deflec tion of light rays by a movable prism, the instrument measures angles and computes the distance, mechanically, accurately, instantly. But distances are so great, and angles so infinitesimally small, that the slighest flaw in the glass, the slightest error in computation or formula, the tiniest deviation in edge or side of the many-angled prisms, will destroy the in strument's usefulness-turn a hit into a miss, perhaps victory to defeat. That we were able in a great emergency to supply our Government, notwith the usual few score, as in former years, but literally with thousands of range-finders, and at no sacrifice of Bausch & Lomb scientific standards That even when working to a thousandth part of a millimeter we have been able to devise machines for large-scale production of range finders, binoculars, gun-sights, aiming-circles, searchlight mirrors, periscopes-all the optical instruments of modern warfare This is both a source of pride to us, and a sug gestion of our equipment for the improvement of optics generally. Write for literatureon any opticalproduct in which you are interested. BAUSCH & LOMB OPTICAL COMPANY . . ROCHESTER, N. Y. Makers of Eyeglass and Spectacle Lenses, Photographic Lenses. Microscopes, Balopticons, Binsaulars. and Engineerine and other Optical Instruments that ees may see better and fart er "Mention The Geographic-It identifies you"