were still used,
although he was able with a single camera to obtain twelve photographs
on successive plates in the space of one second. Marey, like Muybridge,
photographed only one cycle of the movements of a single object, which
was subsequently reproduced over and over again, and the camera was in
the form of a gun, which could follow the object so that the successive
pictures would be always located in the centre of the plates.

The review above given, as briefly as possible, comprises substantially
the sum of the world's knowledge at the time the problem of recording
and reproducing animate movement was first undertaken by Edison. The
most that could be said of the condition of the art when Edison
entered the field was that it had been recognized that if a series of
instantaneous photographs of a moving object could be secured at an
enormously high rate many times per second--they might be passed before
the eye either directly or by projection upon a screen, and thereby
result in a reproduction of the movements. Two very serious difficulties
lay in the way of actual accomplishment, however--first, the production
of a sensitive surface in such form and weight as to be capable of being
successively brought into position and exposed, at the necessarily high
rate; and, second, the production of a camera capable of so taking the
pictures. There were numerous other workers in the field, but they added
nothing to what had already been proposed. Edison himself knew nothing
of Ducos, or that the suggestions had advanced beyond the single
centrally located photographs of Muybridge and Marey. As a matter of
public policy, the law presumes that an inventor must be familiar with
all that has gone before in the field within which he is working, and
if a suggestion is limited to a patent granted in New South Wales, or
is described in a single publication in Brazil, an inventor in America,
engaged in the same field of thought, is by legal fiction presumed to
have knowledge not only of the existence of that patent or publication,
but of its contents. We say this not in the way of an apology for the
extent of Edison's contribution to the motion-picture art, because there
can be no question that he was as much the creator of that art as he
was of the phonographic art; but to show that in a practical sense the
suggestion of the art itself was original with him. He himself says: "In
the year 1887 the idea occurred to me that it was pos