The practical applications of chronophotography are soon seen. Just as machines are driven so as to obtain a useful effect at the smallest expenditure of power, so a man can govern his movements so as to produce the wished-for effects with the least waste of energy, and, consequently, with the least possible fatigue. Of two gaits which can carry us over a definite space in a given time, the one should be preferred which costs the least possible fatigue. Chronophotography furnishes the missing elements of the problem, giving exactly the velocity of the different parts of the body, by the balancing of which we can determine the masses in movement. From a long series of comparisons, important conclusions can be drawn, as, for example, the following: in walking, the most favorable gait is one where step succeeds step at the rate of about one hundred and twenty a minute; for running, the step should be nearly two hundred and forty a minute. Fewer or more numerous steps will give less effect at a greater expenditure of the work. The applications are therefore obvious; they enable us to fix the rate of steps of soldiers to economize as much as possible their strength in the severe trials to which they are subjected. These studies have been followed out at great length, under varying conditions, using a considerable number of subjects; and the results, while not final, have shown that the true method has been found. Experiments have confirmed that which the laws of mechanics could not foretell when the dynamic conditions of the work of man were incompletely known.
FIG. 16.—OSCILLATION OF THE FORE LEG IN A GALLOP. INTERVAL BETWEEN
EXPOSURES ONE TWENTY-FIFTH OF A SECOND.
M. Marey’s studies of the legs of the horse are particularly interesting. We give one [engraving] showing the oscillation of the fore leg of a horse in a gallop.
The analysis of the flight of birds presents special difficulty. Owing to the extreme rapidity of the movements of the wings, an extremely short exposure is required. The direction, often capricious, of the flight of the bird, and the length of the path which must be followed, to include on the sensitized plate sufficiently sharp images, add to the difficulty. Several repetitions of the same experiment are generally required before success.
The photographic gun is particularly valuable for taking photographs of birds. Our [engravings] show the mechanism of the photographic gun and the method of using it.
We present a [photograph] of a gull taken during its flight and an [enlargement] of the same.
The photographic gun will be understood by reference to the [engraving], and is fully described in the “Scientific American Supplement,” No. 386, to which the reader is referred.