. The book of photography; practical, theoretical and applied. n byFig. ITS. Stops to be Used. The method of finding the stops to usewith these tints may best be made clear bya suggested experiment. Suppose an in-terior such as that shown in Fig. 167 isbeing dealt with, it is necessary to use aplate of the speed equal to 28, and to stopthe lens down to ^22 ; then place the meterpointing towards the window or the chiefsource of light. The meter may remainin the picture while the actual exposure is going on. From time to time the stri^j ofbromide paper may be drawn out and ex-amined for an insta
. The book of photography; practical, theoretical and applied. n byFig. ITS. Stops to be Used. The method of finding the stops to usewith these tints may best be made clear bya suggested experiment. Suppose an in-terior such as that shown in Fig. 167 isbeing dealt with, it is necessary to use aplate of the speed equal to 28, and to stopthe lens down to ^22 ; then place the meterpointing towards the window or the chiefsource of light. The meter may remainin the picture while the actual exposure is going on. From time to time the stri^j ofbromide paper may be drawn out and ex-amined for an instant, and as soon as itshows the first sign of darkening, the platein the camera will have been sufficientlyexposed. If a quarter-tint is used, a stopnecessitating four times the exposure, orf45, must be employed ; and for a wholetint one requiring sixteen times the ex-posure. Such apertures, however, are notlikely to be used for interior work if theycan be avoided ; but the whole tint maybe utilised in outdoor photography. Atable is given with the meter which. Fig. 17J.—Wynnes Exposuke Metkk. shows the plate speed and the stopsto be used for the various tints ; by thismeans calculation is entirely avoided, andexposure made as simple as possible. Thesubject number depends on its colour orthe kind of rays which it reflects and thosewhich fall upon it. Mr. Alfred Watkinsgives the following formula:—Sky or sea,slO; snow scenes, extreme distance andseascapes, s25; average landscape, por-traits, buildings, .slOO ; for dark or non-actinic objects in which detail is required,.s200. From these the proportionate ex-posures required by different subjects maybe inferred. EXPOSURE OF THE PHOTOGRAPHIC PLATE. 103 The Infallible Exposure Meter. Another good form of meter is the In-fallible, introduced by Geo. F. Wynne,which selects from the numerous factorsgoverning the exposure three only—light,plate sensitiveness, and stop. This instru-ment is founded upon the same principle asthe Watki
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