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Étienne Jules Marey
Untitled (A man walking at the Physiological Station of Paris)
1883, 30 November
E.J. Marey, "The Physiological Station of Paris, part II", p.708-711, Science, Vol.II, No.42, November 30, 1883, p.710, fig.8.
Partial photographs are also serviceable in an analysis of rapid movements, because by this means the number of attitudes represented may be many times increased. Nevertheless, when the image of a limb is moderately large, the partial photographs cannot be too much increased without confusion through superposition. We must therefore diminish the size of the image, if we desire to repeat them at very short intervals. For this purpose the walker is clothed wholly in black, and narrow bands of some bright metal are placed down his arm, thigh, and leg, following precisely the direction of the bones of these parts. This arrangement allows us to easily increase tenfold the number of images received in a given time on the same plate : hence, instead of ten photographs a second, we can obtain one hundred. For this, the rapidity of rotation of the disk is not altered; but, instead of one opening, there are ten, equally distributed on the circumference. One of these openings must have a diameter twice that of the others. The result is a much larger size for one of the images; and this renders the estimation of the time easy, and also furnishes data to compare the movements of the lower ami upper limbs. The images obtained under these circumstances are so close, that one is present, as it were, at all the successive changes of place of the limbs and body. Thus, in fig. 8, between two successive touches of the ground by the right foot, there are twenty-one different positions of the lower limb. As the foot meets the ground, the knee is bent perceptibly; then it straightens as the foot, resting on the toes, prepares to leave the ground. After the raising of the foot, the knee bends again, and the leg forms with the thigh a right angle ; then it gradually becomes straight, and the sole of the foot, which was at first in a vertical plane, is apparently parallel to the ground which it touches for some time before it rises again. The scale at the bottom of the figure shows that the total length of the step was 2.6 metres. The chronograph was not used in this experiment, but we may estimate the number of images at about sixty a second. The movements of bending and extending the fore-arm are obtained in the same manner as those of the leg. The turnings of the head are expressed by the imdulatory motion of a bright point placed on a level with the ear. In short, the diminutions and the accelerations of each part are expressed by the crowding or separation of the images. To ascertain the corresponding positions of the arm and leg at a given instant, we take for data every fifth figure, which is larger than the others. These images are formed at the moment of passage before one of the larger openings; and they correspond, therefore, to the same Instant of time.