The principle of the instrument was suggested to Edison by the zoetrope,
and of course, he well knew what Muybridge had accomplished in the
line of motion pictures of animals almost ten years previously. Edison,
however, did not employ a battery of cameras as Muybridge had done,
but devised a special form of camera in which a long strip of sensitized
film was moved rapidly behind a lens provided with a shutter, and so
arranged as to alternately admit and cut off the light from the moving
object. He adjusted the mechanism so that there were 46 exposures a
second, the film remaining stationary during the momentary time of
exposure, after which it was carried forward far enough to bring a new
surface into the proper position. The time of the shifting was about
one-tenth of that allowed for exposure, so that the actual time of
exposure was about the one-fiftieth of a second. The film moved,
reckoning shiftings and stoppages for exposures, at an average speed
of a little more than a foot per second, so that a length of film of
about fifty feet received between 700 and 800 impressions in a circuit
of 40 seconds.

Edison named his first instrument the kinetoscope. It came out in 1893.
It was hailed with delight at the time and for a short period was much
in demand, but soon new devices came into the field and the kinetoscope
was superseded by other machines bearing similar names with a like
signification.

A variety of cameras was invented. One consisted of a film-feeding
mechanism which moves the film step by step in the focus of a single
lens, the duration of exposure being from twenty to twenty-five times
as great as that necessary to move an unexposed portion of the film
into position. No shutter was employed. As time passed many other