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Auxiliary

paper, passes, tank and vat

AUXILIARY EXPOSURE.—The sensitive dry-plate, either before or after exposure in the camera, is exposed for a fraction of a second to a weak, diffused light. This method has been several times recommended by competent authorities for under-exposed negatives, and softer effects are stated to be the result.

AUXOMETER.—An instrument to determine the magnifying power of an optical system.

AVOIRDUPOIS.—The name of a system of weights. See Weights and Measures.

AXIS.—The axis of a lens is an imaginary line passing through the centre of its curved and at right angles with its plane surface. A ray of light passing along it is the only one that is not refracted. See Optics.

the platen, and press the platen upward against the underside of the paper, placing the sensitive side of the latter in contact with the negative during the interval of exposure to the electric lights (usually two seconds); it is then drawn down until a fresh section of paper passes under the negative and the operation repeated. The movement is quite similar to the platen of a printing press.

Fig. 45 shows the arrangement employed for developing the exposed paper. The paper after passing over the submerged roll and down again, thence up out of the tank over the roll between the first and second tanks and down into the fresh ferrous oxalate developer in this tank, shows the images half developed out.

Coming out of the second tank, the images are fully developed, thence the paper passes on into the third vat, con taining dilute acetic acid, which dissolves all of the iron left in the paper from the developer, and acts as a check to further development, thence in the next vat the paper is washed with water ; next it passes into a fixing vat containing a solution of hyposulphite of soda, is again washed in the following tank then it passes into a vat of alum water, which hardens the film, and finally goes through two or three vats of water, receiving final spraying, as shown in Fig. 45.

From the last spraying it is led on to an endless canvas carrier into a long inclosed chamber filled with a current of warm air, heated by a gas furnace at the end. At the end of this heated chamber the paper comes out perfectly dry, and is rolled up with the pictures all on it. When the run is complete the roll of pictures is un wound, they are cut off to the respective sizes desired, and mounted in the usual way.