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IMPROVEMENTS IN HIGH-SPEED PICTURES 463
passed to record composite position pictures of a moving subject. Since the process is continuous, the question of how many position pictures are recorded in this manner before double exposure takes place becomes an important one, and one for which the answer is not immediately obvious. As a starting point, one might say that for every one-thousandth-inch movement of the grid, an entirely new picture could be recorded. On that basis and the grid dimensions given we could profess to be able to record thirty composite-position pictures on one plate before double exposure results. If that were the case, during playback for observation it would be necessary to index the analyzing grid one thousandth of an inch to observe a new position picture of a moving object, a total indexing of thirty thousandths of an inch thus passing the thirty position pictures across the screen for observation. Even with this assumption one can visualize the large number of pictures per second possible by this method, a linear grid velocity of only approximately one-half mile per hour giving ten-thousand position pictures per second.
That the above assumption fortunately is pessimistic, and that a great many more position pictures of the moving object are actually present after 0.030 inch of grid translation, can readily be demonstrated. With some thought it becomes apparent that the absolute number of pictures of, say, the leading edge of a moving object is more a function of how many grains of emulsion are uncovered per 0.030 inch of travel than a function of the number of slit widths uncovered. The total number of "frames" for a grid-type camera would be determined by the accuracy of one's analysis of the exposed plate. Concrete basis for this claim is the fact that when an exposed high-speed composite-picture plate is examined with an analyzing grid, subject motion can be observed when the grid is moved less than the transparent line width or less than one thousandth of an inch. These minute subject advances can be seen readily in the table viewer. However, they can be better shown to a larger audience by a 16-mm demonstration film.
The first section of this film shows the smoothness of subject motion when a plate carrying composite motion picture frames is examined through a continuously moving grid. The motion pictures were taken continuously of the picture area as the grid scans the photographic plate. About two hundred 16-mm frames were exposed during the 0.030-inch excursion. The film demonstrated that the subject motion is extremely smooth and the picture detail is nearly