. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 320 HISTORY OF CHRONOPHOTOGRAPHY. at the same time to ^ive them precision. The principle of the first method emploj'ed was as follows: Suppose an ordinar}^ camera to be pointed at a perfectly dark field, and that an opaque disk in front of the lens is pierced with narrow openings and turns about its centej'. Every time an opening passes before the objective the light would be admitted, if there were an}^ light in the field. But there being
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 320 HISTORY OF CHRONOPHOTOGRAPHY. at the same time to ^ive them precision. The principle of the first method emploj'ed was as follows: Suppose an ordinar}^ camera to be pointed at a perfectly dark field, and that an opaque disk in front of the lens is pierced with narrow openings and turns about its centej'. Every time an opening passes before the objective the light would be admitted, if there were an}^ light in the field. But there being no light, none penetrates the camera; and w^hen the plate is developed it is seen not to have been affected. If a strongly lighted man or animal were to cross the dark field, each admission of light would produce an image of the animal, and as the latter moved, photographs of it would be taken on the plate at different places and in different attitudes. Such an arrangement, however, would not answer. Fig. -i shows the apparatus in its real form. Within a cubical box is seen the camera with its lens. Behind it is the plate holder or back, C, which slides in grooves. Between the plate holder and the camera revolves the slitted disk grazing the sensitive plate—in short, what is called a plate-shutter. This disk, D, with its narrow openings, f, is worked by a clock move- ment furnished with a speed governor, and is set in mo- tion by a handle. Fig. 5 (PI. I) shows the flight of a white duck, which passes ))efore the dead black back- ground. The succession of images is from left to right. Eight different attitudes are shown during one complete stroke of the wings. The}^ reveal the details of the mechanism of flight. In order to appreciate the dimensions of the animal and the extent of its tlight, a divided rule is placed before the dark field. It is photographed and serves as a scale. Finally, in order to show the intervals of time between the successive images, at the lower right
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