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to be projected. But inasmuch as these various standards will all come up for our consideration, each in its own good time, I need not enlarge further along this line.
Some of these standards will be found to be determined by custom, economy, or any of the many obvious considerations, while others will not be matters of choice at all, but will be derived from other standards.
Those standards which are matters of choice may be anything you please ; such as three sprocket holes to the picture if you wish, and think you can make the innovation attractive to the majority. This ia purely a matter of expediency. But the precision limits of these sprocket holes is not a matter of choice. Their size, shape and position in relation of the dividing line — choice again, but not the amount of vibration in the size, shape or position.
The variations in size may have a certain precision limit along one axis, and a precision limit of a whole order higher along the other — the length of the sprocket hole might vary by as much as plus or minus 1/1, 000th of an inch; while a plus or minus variation of 1/1 0,000th of an inch in the width of the sprocket hole might produce a disturbing efifect on the screen. And then again there are important and involved relationships which will prove to be of moment in the determination of precision limits. For instance, take the case of a mechanic's scale as a standard of linear measure, and even though it has suffered abuse it is still good enough as a standard with which to measure say, a few lengths of gas pipe — a low order of precision is perfectly satisfactory here; but if this same scale were to be used to measure the change in length of a short piece of film, with the change in grains of water per cubic foot of air, then it would be necessary to know at what temperature the scale was standard; and if used at any other temperature, its coefficient expansion, that corrections could be made to compensate for the scales departure from standard. It is important that this involved relationship should be borne in mind when considering the precision limits of standards.
But who then, is to determine these important precision limits and how? I do not mean the standards — some are still matters of choice — others are irrevocably fixed by custom, while still others will be found to be fixed by the requirements of their precision limits.
Gentlemen, there is one standard of transcendental importance, and when we have once defined it, then any of us can satisfy himself as to the precision limits of any other standard suggested, by the mere expedient or performing a few simple sums in arithmetic. But until this supreme standard is defined, no concordant precision relationship between such standards as there may be, can be hoped tor.
Take the matter of projection speed — in any terms you like, such as pictures per second, feet per minute — intermittent R. P. M. — they may all be converted into the number of phase pictures presented to the eye in unit time. If there is no phase difference, that is no motion of the object photographed, then so far as the spec