Part 2 (1/2)

The negative plates were supplied by the Cramer Dry Plate Company of St.

Louis, and the positive plates by the Carb.u.t.t Company of Philadelphia. On a favorable day five hundred or six hundred negatives were sometimes exposed; on one day the number of exposures reached seven hundred and fifty.

The electrical manipulations were directed by Lino F. Rondinella; the development room was in charge of Henry Bell. The author takes pleasure in acknowledging the skill, patience and energy which these gentlemen exhibited in their respective fields of labor.

Although the one six-thousandth part of a second was the duration of the most rapid exposure made in this investigation, it is by no means the limit of mechanically effected photographic exposures, nor does the one-sixtieth part of a second approach the limit of time intervals. Marey, in his remarkable physiological investigations, has recently made successive exposures with far less intervals of time; and the author has devised, and when a relaxation of the demands upon his time permit, will use an apparatus which will photograph twenty consecutive phases of a single vibration of the wing of an insect; even a.s.suming as correct a quotation from _Nicholson's Journal_ by Pettigrew in his work on Animal Locomotion that a common house fly will make during flight seven hundred and fifty vibrations of its wings in a second of time, a number probably far in excess of the reality.

The ingenious gentlemen who are persistently endeavoring to overcome the obstacles in the construction of an apparatus for aerial navigation, will perhaps some day be awakened by the fact that the only successful method of propulsion will be found in the action of the wing of an insect.

We will now resume the subject proper of this monograph.

It is impossible within its limits to trace the history of the art of delineating animals in motion, or to ill.u.s.trate it with examples of the truthful impressions of the primitive Artists, or of the imaginative and erroneous conceptions of many of those of modern times. Certain phases of the facts of Animal Locomotion will alone be treated upon, as demonstrated by photographic research.

The ill.u.s.trations and condensed definitions of the various gaits were prepared by the Author for the ”Standard Dictionary.” Before studying these it is essential that the meaning of the terms _step_ and _stride_ should be distinctly understood.

A STEP is an act of progressive animal motion, in which one of the supporting members of the body is thrust in the direction of the motion and the support transferred, wholly, or in part, from one member to another.

A STRIDE is an act of progressive animal motion, which, for its completion, requires all of the supporting members of the body, in the exercise of their proper functions, to be consecutively and regularly thrust in the direction of the movement until they hold the same relative positions in respect to each other as they did at the commencement of the notation. In the bipedal walk or run a step is one-half of a stride or full round movement. With all quadrupeds, except the kangaroo and other jumpers, _four_ steps are necessary to complete the stride.

THE WALK.

The WALK is a method of progressive motion with a regular individual succession of limb movements. In the evolution of the terrestrial vertebrates the walk was probably the first adopted method of locomotion, and its execution is regulated by the law that the movement of the _superior_ limb precedes the movement of its lateral _inferior_ limb. This is proved not merely by the _ordinary_ quadrupedal walk, but by the suspended motion of the sloth; the crawling of the child upon the ground, the erect walk of man; and the inverse limb movements of the ape tribe.

The relative time intervals of the foot-fallings vary greatly with many species of animals, and even with the same animal under different conditions.

Selecting the horse for the purpose of ill.u.s.tration we find that during the walk--his slowest progressive movement--he has always two, and for a varying period of time, or distance, three feet on the ground at once, while during a very slow walk the support will devolve alternately upon three feet and upon four feet.

[Ill.u.s.tration: SOME CONSECUTIVE PHASES OF THE WALK.]

If the notation of the foot-fallings commences with the landing of the right hind foot, the order in which the other feet are placed upon the ground will be: the right fore, the left hind, and the left fore, commencing again with the right hind.

a.s.suming that our observation of the stride of a horse during an ordinary walk commences with the landing of the right hind foot, the body will then be supported by both hind and the left fore feet. The left hind is now lifted, the support of the body devolves upon the diagonals--the right hind and left fore--and continues so supported until the left hind is in the act of pa.s.sing to the front of the right; when the right fore is next placed on the ground. The left fore is now raised, and the body is supported by the right laterals, until the landing of the left hind foot relieves its fellow hind of a portion of its weight. Two steps or one-half of a stride have now been made, and with the subst.i.tution of the right feet for the left, two other steps will be executed in practically the same manner, and a full stride will have been completed. We thus see that during the walk a quadruped is supported by eight different methods, the supporting limbs being consecutively:

Both hind and left fore.

Right hind and left fore _diagonals_.

Right hind and both fore.

Right hind and right fore _laterals_.

Both hind and right fore.

Left hind and right fore _diagonals_.

Left hind and both fore.

Left hind and left fore _laterals_.

Followed as at the commencement with both hind and left fore.