It is on account of this variability in the frame rate at which films were both shot and projected in early cinema that in many film catalogues covering this period, it is the physical length of the films that is indicated rather than temporal duration.
However, for most readers of The Silent Time Machine website, physical lengths will mean little. When one learns that the Austrian ethnographic film pioneer, Rudolf Pöch, recommended shooting sequences of no more than 20 metres, what does that mean exactly? Or when Margaret Mead and Gregory Bateson are said to have shot an unprecedented 22,000 feet of film, it sounds like a great deal, but how much is it really?
In order to get some sense of the duration of these examples, it is first necessary to be aware that the Pöch was shooting on 35mm film (in which there are 16 frames per foot of film) while Mead and Bateson were shooting on 16mm (in which there are 40 frames per foot of film). If one assumes that in both cases, the films were shot at 16fps, this means that the duration of the ideal sequence for Pöch was 65 seconds, while the Mead and Bateson material totalled just over 15 hours of footage.
These calculations of duration are based on the assumption that the material was shot at a frame rate of exactly 16fps which, for the reasons described here, is far from being necessarily the case. However, provided this caveat is born in mind, temporal duration is arguably a more meaningful indicator of quantity than a bald statement of physical length.