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.

When, therefore, during a walk, a horse is supported on two legs, with two feet suspended between them, each pair are laterals. On the other hand, when the suspended feet are respectively in advance of, and behind the supporting legs, each pair are diagonals.

These invariable rules have been unknown or ignored by many distinguished artists of modern times.

THE AMBLE.

The amble is a method of progressive motion with the same sequence of foot fallings as the walk, but in which a hind foot or a fore foot is lifted from the ground in advance of its fellow hind foot or its fellow fore foot being placed thereon. The support of the body therefore devolves alternately upon a single foot and upon two feet; the single foot being alternately a hind foot and a fore foot, and the two feet being alternately laterals and diagonals. At no time is the body entirely unsupported.

The following series of ill.u.s.trations will clearly demonstrate the consecutive foot fallings and some characteristic phases of an ambling stride:

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

The amble has various local names, such as the "single foot," the "fox trot," etc. It has sometimes been erroneously confused with the rack or the so-called "pace;" it is the most gentle and agreeable to the rider of all methods of locomotion of the horse, while the rack is the most ungraceful and disagreeable.

In Scott's romances are many allusions to the "ambling palfry." Ben Jonson in "Every Man in His Humor" speaks of going "out of the old hackney-pace to a fine, easy amble," and d.i.c.kens in "Barnaby Rudge" refers to "the gray mare breaking from her sober amble into a gentle trot."

The ambling gait is natural to the elephant, and to the horse, the mule and the a.s.s; but in many countries these latter animals are not encouraged in its use.

THE TROT.

The trot is a more or less rapid progressive motion of a quadruped in which the diagonal limbs act nearly simultaneously in being alternately lifted from and placed on the ground, and in which the body of the animal is entirely unsupported twice during each stride.

Selecting for the purpose of ill.u.s.tration the phases occurring during two steps or one-half of a stride of 18 feet in length by a horse trotting at the rate of a mile in two minutes and twelve seconds, we find that at the instant his right fore foot strikes the ground, the left hind foot is a few inches behind the point where it will presently strike. As the feet approach the ground, the right hind leg is drawn forward with the pastern nearly horizontal, while the left fore leg is flexed under the body. After the feet strike the ground and the legs approach a vertical position the pasterns are gradually lowered, and act as springs to break the force of the concussion until they are sometimes bent to a right angle with the legs.

At this period the fore foot is raised so high as to frequently strike the elbow, while the diagonal hind foot is comparatively but little above the ground, and is about to pa.s.s to the front of the left hind.

The pasterns gradually rise as the legs pa.s.s the vertical until the right fore foot has left the ground and the last propelling force is being exercised by the left hind foot; which accomplished, the animal is in mid air.

The right hind foot continues its onward motion until it is sometimes much in advance of its lateral fore foot, the former, however, being gradually lowered, while the latter is being raised. The right hind and both fore legs are now much flexed, while the left hind is stretched backwards to its greatest extent with the bottom of the foot turned upwards, the left fore leg is being thrust forwards and gradually straightened, with the toe raised as the foot approaches the ground; which accomplished, with a subst.i.tution of the left limbs for the right, we find them in the same relative positions as when we commenced our examination, and one-half of the stride is completed.

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

With slight and immaterial differences, such as might be caused by irregularities of the ground, these movements are repeated by the other pair of diagonals, and the stride is then complete.

If the stride of a trotting horse is divided into two portions, representing the comparative distances traversed by the aggregate of the body while the feet are in contact with, and while they are entirely clear of, the ground, the relative measurements will be found to vary very greatly, they being contingent upon length of limb, weight, speed, and other circ.u.mstances.

Heavily built horses will sometimes merely drag the feet just above the surface, but, in every instance of a trot, the _weight_ of the body is really unsupported twice during each stride. It sometimes happens that a fast trotter, during the four steps of a stride, will have all his feet clear of the ground for a distance exceeding one-half of the length of the entire stride. Upon landing, a fore foot almost always precedes its diagonal hind.

It will be observed in the ill.u.s.trations that while during the fast trot the fore feet are lifted so high that they frequently strike the breast, the hind feet are raised but little above the surface of the ground. The trot is common to all the single-toed and to nearly all the cloven-footed and soft-footed animals. It has, however, not been recorded as being adopted by the elephant, the camel, or the giraffe.

THE RACK.

The rack, sometimes miscalled the "pace," is a method of quadrupedal locomotion in which two lateral feet with nearly synchronous action are placed upon and lifted from the ground alternately with the other laterals, the body of the animal being in the intervals entirely without support. The distance which the propelling feet hurl the animal through the air depends, as with other movements, upon a variety of circ.u.mstances; at a high rate of speed the distance will be about one-half the total length of the stride.

Upon landing, a hind foot usually precedes its lateral fore.

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

The rack is an ungraceful gait of the horse, and disagreeable to those who seek comfort in riding.