Part 2

A shaft, connected by an arrangement of geared wheels to the drum, passes through the center of the segmented ring and carries a loose collar; a stout metal rod is firmly attached near its longitudinal center to this loose collar. One arm of the rod carries a laminated metal scraper, or contact brush, arranged to travel around the periphery of the ring, and in its revolution to make contact with each segment in succession. The contact brush is connected through the arm with one pole of the battery; and each segment--through its independent wire and magnet of the electro-exposors--with the other pole.

When twenty-four consecutive phases of an act of motion are to be photographed from one point of view, all of the insulated segments in the ring are put in circuit. When twelve consecutive phases are to be photographed synchronously from each of three points of view, each alternate segment is placed in circuit with the electric battery.

The manner in which the series of synchronous exposures is effected will be readily understood by reference to the diagram, 8.

All being in readiness, and the weights and fan wheel adjusted to cause the contact brush to sweep over the periphery of the ring at the required rate of speed, the drum, and with it the shaft is set in motion.

At the proper time, pressure on a button completes an independent circuit through the magnet seen below the segmented ring, figure 7, and in the side diagram of figure 8.

The action of the armature releases the lower end of the rod on the loose collar, which, by means of a coiled spring, is immediately thrown into gearing with the already revolving shaft; the contact brush sweeps around the segmented ring and effects the consecutive series of exposures at the pre-arranged intervals of time.

At the University the intervals varied from the one-sixtieth part of a second to several seconds.

A record of these time intervals was kept by a chronograph, a well known instrument; it comprises a revolving drum carrying a cylinder of smoke-blackened paper, on which, by means of successive electric contacts, a pencil is caused to record the vibrations of a tuning fork, while a second pencil marks the commencement of each photographic exposure. The number of vibrations occurring between any two successive exposures marks the time. The tuning fork used made one hundred single vibrations in a second of time. To ensure greater minuteness and accuracy in the record, the vibrations were divided into tenths, and the intervals calculated in thousandths of a second.

For the purpose of determining the synchronous action of the electro-exposors while making a double series of exposures, the accuracy of the time intervals as recorded by the chronograph, and the duration of the shortest photographic exposures used in the investigation, the two batteries of portable cameras were placed side by side, and the exposors were each connected with the exposing motor by separate lengths of a hundred feet of cable. The two series of cameras were pointed to a rapidly revolving disc of five feet diameter. The surface of the disc was black, with narrow white lines radiating from the center to the edge like the spokes of a wheel. A microscopic examination of the two series of resulting negatives proved that no variation could be discovered in the synchronous action of ten of the duplicated series of exposures, and that in the remaining two a variation existed in the simultaneity of a few ten-thousandths of a second--a result sufficiently near to simultaneity for all ordinary photographic work.

A reproduction of the chronographic record of one of these experiments is seen in figure 9.

The first line records the revolution of the disc; the second the vibration of the tuning fork; and each group of three long double markings in the third line indicates a photographic exposure.

The shortest exposures made at the University were--approximately--the one six-thousandth part of a second; such brief exposures are however for this class of investigation very rarely needed.

Some horses galloping at full speed will, for a short distance, cover about fifty-six or fifty-eight feet of ground in a second of time; a full mile averaging perhaps a hundred seconds. At this speed, a foot recovering its loss of motion will be thrust forward with an occasional velocity of at least 120 lineal feet in a second of time.

During the one one-thousandth part of a second the body of the horse will at this rate move forward about seven one-tenths of an inch, and a moving foot perhaps one and a half inches, not a very serious matter for the usual requirements of the amateur photographer.

A knowledge of the duration of the exposures, however, was in this investigation of no value, and scarcely a matter of curiosity, the aim always being to give as long an exposure as the rapidity of the action would permit, with a due regard to the necessary sharpness of outline, and essential distinctness of detail.

The power used for operating the magnets, through the exposing motor, was given from a lé Clanché battery of fifty-four cells, arranged in multiple arc of three series, each of eighteen cells.

During the investigation at the University of Pennsylvania, more than a hundred thousand photographic exposures were made.

The negative plates were supplied by the Cramer Dry Plate Company of St. Louis, and the positive plates by the Carbutt 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 assuming 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 illustrate 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 illustrations 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 illustration 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.

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.

Assuming 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 passing 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 substitution 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 illustrations will clearly demonstrate the consecutive foot fallings and some characteristic phases of an ambling stride:

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 Dickens 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 ass; 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 illustration 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 pass to the front of the left hind.

The pasterns gradually rise as the legs pass 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 substitution 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.

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 circumstances.

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 illustrations 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 circumstances; 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.

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

The movements hitherto described are regular in their action, and a stride may be divided into two parts, each of which--with a change of limbs--is practically similar to the other; we now come to methods of progression which cannot be so divided, and each stride must be considered as a unit of motion.

THE CANTER.

In the canter we discover the same sequence of foot fallings as in the walk, but not with the same harmonious intervals of time. The gait resembles the gallop in respect to its leaving the horse entirely unsupported for a varying period of time, and in the fact that the spring into the air is always effected from a fore foot, and the landing upon the diagonal hind foot; in other respects it materially differs from that method of progression.

Assuming that during a stride of the canter a horse springs into the air from a left fore foot, the right hind foot will first reach the ground; the two fore legs will at this time be flexed under the body, the right being the first landed, and for a brief period of time the support will devolve upon the laterals. The right fore foot is rapidly followed by the left hind. During a very slow canter the other fore foot will sometimes be landed in advance of the lifting of its diagonal, and the curious phase presented of all of the feet being in contact with the ground at the same instant. Usually, however, the first hind foot to touch the ground will be lifted, and the support thrown upon the diagonals.

The left fore is now brought down, and is followed by the lifting of the right fore; when the left laterals assume the duty of support. The left hind is now raised, and with a final thrust of the left fore foot the animal is projected into the air, to land again upon its diagonal, and repeat the same sequence of movements.

The above phases are selected from a single complete stride, in which the landing occurs on the _right_ hind foot. Had the horse sprung from a _right_ fore foot, the right and left feet would have been reversed through the entire series.

THE GALLOP.

The gallop is the most rapid method of quadrupedal motion; in its action the feet are independently brought to the ground; the spring into the air as in the canter is effected from a fore foot, and the landing upon the diagonal hind foot.

The phases illustrated are selected from the stride of a thorough-bred Kentucky horse, galloping at the rate of a mile in a hundred seconds, with a stride of about twenty-one lineal feet.

The length of stride and the distance which the body is carried forward without support depend upon many circumstances, such as the breed, build and condition of the horse, speed, track, etc.

The phases illustrated and the measurement given apply to one stride of one horse, but may be considered as fairly representing the stride of a first-class horse in prime racing condition at the height of his speed, upon a good track.

Assuming--as in this instance--the springing into the air to have been effected from the right fore foot, the landing will take place in advance of the centre of gravity, upon the diagonal, or left hind foot; above, will be suspended the right hind foot, and at a higher elevation, several inches to the rear, will be the right fore foot, with the sole turned upward. The left fore leg will be in advance of the right, and also flexed. The force of the impact and the weight of the horse causes the pastern to form a right angle with the leg, and the heel is impressed into the ground.

The right hind foot strikes the ground and shares the weight of the body. The left hind foot leaves the ground while the right hind pastern is in its horizontal phase, supporting all the weight. At this period the left fore leg is perfectly straight, with the toe much higher than the heel, and is thrust forward until the pastern joint is vertical with the nose, the right fore knee is bent at a right angle. The left fore foot now strikes and these diagonals are for a brief period upon the ground together. The left fore leg, however, immediately assumes the entire responsibility of support and attains a vertical position, with the pastern at a right angle. The right fore leg becomes perfectly rigid, and is thrust forward to its fullest extent. The right fore foot now strikes the ground, the two fore legs form a right angle, and the hind feet are found thrust backward, the right to its fullest extent. The left fore leg having completed its functions of support, is now lifted, and the weight transferred to the right fore foot alone, which is soon found behind the centre of gravity; the left hind foot passes to the front of the right fore leg, which, exercising its final act of propulsion, thrusts the horse through the air; the left hind foot descends; the stride is completed, and the consecutive phases are renewed. From this analysis we learn that if the spring is made from the right fore foot during the rapid gallop of a thoroughbred horse, it is supported consecutively by

The left hind foot.

Both hind feet.

The right hind foot.

The right hind and the left fore feet.

The left fore foot.

Both fore feet.

The right fore foot.

From which he springs into the air to re-commence the phases with the left hind foot, while the only phase in which he has been discovered without support is one when the legs are flexed under the body. All of the feet at this time are nearly close together and have comparatively little independent motion; this phase, therefore, more persistently than any other, forces itself upon the attention of the careful observer, and conveys to him the impression of a horse's rapid motion in singular contradiction to the conventional interpretation, until quite recently, usually adopted by the Artist.

It should not be understood that the term "spring" implies that the body of the horse is greatly elevated by that action; were it so, much force would be unnecessarily expended with the result of loss of speed. The center of gravity of a horse trotting or galloping at a high rate of speed will preserve an almost strictly horizontal line, the undulations being very slight.

In the gallop of the horse it is probable there may be sometimes a period of suspension between the lifting of one fore foot and the descent of the other, but it has not yet been demonstrated.