Numbering devices in cameras, 169 Oblique views, 39, =320= angles at which taken, 40, 321 exposures for, 69 filters for, 242 use of hand cameras for, 95 Observer, function of in aerial photography, 291, 295, 304 Oil spray from motor, 214 Opacity, 228 Opening for camera, 211 Opposite directions, shutter to move alternately in, 76, 139 Orthochromatic plates, 233 Overlaps, for mapping, 307 for stereoscopic views, 40 on a turn, 64, 139 Panchromatic emulsions, 233 plates, 49, 238 Panoramic views, 321 Parallax method of focussing, 65, 66 Parallel, flying in, 308 Photographic planes, special, 213 Pilot, function of, in aerial photography, 291, 295 Pinpoints, 39, 291 Pistol grip for hand cameras, 95, 96 Plate holders, 87 Plates, bathed, 235 behavior of compared to film, 237 color sensitive, 233 iso- and ortho-chromatic, 233 panchromatic, 233 satisfactory kinds for aerial work, 238 self screening, 245 shape of, 63 size of, 43, 62 Plumb line, behavior in banking plane, 28 Ply-wood veneer construction, 23, 211 Positype paper, 238 Potassium carbonate for drying plates, 276 Power required to drive cameras, 125 Pressure, of shutter curtain, 131 plate, for holding film flat, 131, 141 Printing, =279= contact, 279 machines, 279 media, 252 Prints, paper, 253 development of, =286= Prisms for oblique photography, 324, 326 Propeller, characteristics, 152 constant speed, 129, 159 drive for cameras, 102, 116, 119, 135, 136, 144, 157, 158 position of, 120 variable speed, 159 Pump, for producing suction on film, 132 Punch marks on film, 144, 272 Pyro developer, 261 Racks, negative, 271 Real estate, aerial mapping of, 393 Rectifying, 286, 305 camera, 314 Reduction of aerial negatives, 262 Release, shutter, 96, 99 duplicate, for pilot, 164 Release, shutter, time controlled, 124 Relief, criterion for correct, 335, 344 exaggerated, 337 impression of, produced by motion, 349 Resolving power of plates, 59, =235=, 260 Richard stereo printing frame, 283, 348 Rinsing of plates, 259 Rubber, sponge, use of in camera mountings, 195, 203 Safe lights, photographic, 269 Safety catch on camera mounting, 203 device on camera driving mechanism, 162 Salvaging of ships, aerial photography and, 399 Seaplane, 25, 374 Self screening plates, 245 Semaphore signalling in plane, 297 Semperfocal enlarging camera, 284 Sensitized materials, requirements for, 225 Sensitometry, =227= of papers, 253 Shadows, compass directions from, 356 proper direction for, in examining prints, 352 Shaft, flexible, 119, 123, 142, 161 Sheaths, plate, 87, 88, 93, 126, 170 Shrinkage, film, 237, 317 paper, 285, 315, 317