Exposure 
TIMING SHUTTER SPEEDS.—Using a pendulum for this 
purpose, the speed of the bob is in feet per second 
2x gl( sin’ 2 sin’ S 
in which g = force of et at the eres of experiment, 
32.2 being sufficiently approximate, ] = length of pendulum 
in feet, B the angular displacement from vertical of bob at its 
highest position, C the angular displacement from vertical of 
bob for position at which speed is required. From this a 
table can be calculated of the speeds of the bob over each 
5 degrees of arc and also the total period of the pendulum 
(Collingridge). 
THE AMERICAN PHOTOGRAPHY EXPoSURE-TABLES.*— 
Find numbers for subject, stop, light, month and hour, and 
plate. Add them, refer to table (page 60), and give exposure 
indicated. When the exposure fails to correspond with speed 
marking on shutter, use the nearest shutter speed, preferably 
the lower. 
Subject.— 
Beam(omlyy) ane Cloudsy ick. .cialcie aeac ey acetate yy 
Sea views, snow scenes, distant landscape ............ 1 
Open landscape with unimportant foreground ......... 2 
Ewer celandscape with TOresround sik yoo uu ued 3 
Landscape with dark foreground, groups in sunlight .... 4 
SPReeR scenes, /DUidings SroUps {28.2 ee es 5 
EGMeMES VTP SHAC es NL LV i 5) VMI irony 2 7 
HTGOOTNPOTETAIES: sie. eS Re ge eat) 8 to 10 
RESETS Me ey Ns A ON lay dle a (lds SU UMtMaM EN parla) 0 8 to 16 
* Copyright, 1906 by F. Dundas Todd. Copyright, 1911, 1913, 1914, by 
F. R. Fraprie. Copyright, 1912, 1915, 1916, by American Photographic 
Publishing Co. 
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