of time. From the negatives secured in this way a series of positives
were obtained in proper order on a strip of sensitized paper. The strip
when examined by means of the Zoetrope furnished a reproduction of the
horse's movements.

The Zoetrope was a toy familiar to children; it was sometimes called
the wheel of life. It was a contrivance consisting of a cylinder some
ten inches wide, open at the top, around the lower and interior rim
of which a series of related pictures were placed. The cylinder was
then rapidly rotated and the spectator looking through the vertical
narrow slits on its outer surface, could fancy that the pictures inside
were moving.

Muybridge devised an instrument which he called a Zoopraxiscope for
the optical projection of his zoetrope photographs. The succession of
positives was arranged in proper order upon a glass disk about 18
inches in diameter near its circumference. This disk was mounted
conveniently for rapid revolution so that each picture would pass in
front of the condenser of an optical lantern. The difficulties involved
in the preparation of the disk pictures and in the manipulation of the
zoopraxiscope prevented the instrument from attracting much attention.
However, artistically speaking, it was the forerunner of the numerous
"graphs" and "scopes" and moving picture machines of the present day.

It was in 1887 that Edison conceived an idea of associating with his
phonograph, which had then achieved a marked success, an instrument
which would reproduce to the eye the effect of motion by means of a
swift and graded succession of pictures, so that the reproduction of
articulate sounds as in the phonograph, would be accompanied by the
reproduction of the motion naturally associated with them.