In the aggregate these improvements have greatly added to the utility of wheeled vehicles, and their introduction of late years has enonnously increased. To what extent this has been the case may be judged from the statement made at a recent convention of the Carriage-builders' National Association, that in the State of Ohio alone there are built each year more pleasnre-carriag-es than are built in England, Scotland, Ireland, France, and Germany combined. The value of the carriag-es and wagons manu factured and sold in the United States, annually, was estimated some years ao-o at one hundred million dollars.
6 Arrangement and Size- of the technical description which has been given in what has preceded, it is evident that to preserve the wagon-body in a horizontal position the front wheels must be lower than the rear ones. This arrangement not only contributes to the ease of motion of the vehicle, but also permits of the attachment of the traces in a more advantageous position. The size of the wheels of vehicles is of importance. This element varies greatly according to the use for which the wagon is intended. Thus, for rapid vehicles, the diameter of the front wheels may be from 23/t to 3 feet, and that of the hind wheels from 4 to 4Y, feet; on heavy freight-wagons, on the other hand, it may be, for front and hind wheels, from 3 to 3y, feet and from to feet, respectively. The poorer the road, other things being equal, the larger should be the wheels, since experiment has demonstrated that for a given load the required trac tive force on broken-stone roads and paved streets is approximately in versely proportioned to the radius of the wheel.
The IMeel in Relation to the the pressure of a wheel upon tbe road diminishes proportionately with the increase in tbe width of its felly, and since this pressure must not exceed a certain maximum, lest the road be utterly ruined, laws have been enacted in different countries defin ing the minimum permissible width of felly for different wheel-loads. By the rule established by the experiments of Morin and Dupoint, 273 pounds of load may be allowed for each -1 inch of width of felly, and, as extreme limits for the latter, from 2K3 to 43/4. inches. Respecting the weights of the vehicles themselves there are the widest variations, the ex.treme range be ing from ninety-five pounds in the lightest pleasure-carriage to five tons for the heaviest freight-wagons.
Tractive resistance to be overcome by a moving wagon will depend on its construction, the condition of the road, and the rate of speed, and it will vary between very wide limits. According to I3ockel berg, the coefficient of resistance—namely, the ratio of the tractive force to the total weight to be moved—may be assumed to be, on stone roads, to -1- nd on earth roads from to -1 75, a 5 2 0 Animal drawing-power of the draft animals by which the resistance above-named must be overcome will depend on their race, build, bodily condition as regards nourishment, and weight. On the aver age the tractive force that will be exerted by an animal motor mav be taken at one-fourth its weight, so that for freight-wagons heavy horses must be chosen. With one and the same animal, the tractive force exerted, the
time in which the work is done, and the speed with which the load is moved are related to one another, so that an alteration of the value of one of these factors implies the alteration of the other two, unless the animal be overworked. Thus, under normal conditions, an animal must put forth only so much power during- a p.-,iven time at a given speed. If it is required to put forth more power than this, then it must be either at a lower rate of speed or for a shorter time. Furthermore, each animal has a normal gait or rate of speed, to maintain which he will require neither to be driven nor held back. These data have been carefully worked out and mathemat ically expressed by Maschek. The effective work of a horse mav be stated in the following terms: The average load which a single horse can draw at the rate of twenty miles per day (of ten hours) in a cart or wagon weighing 7 cwt. is ISoo pounds.
/-/arnessing.—Furthermore, the mode of harnessing has a decided in fluence upon the work the animal is able to perform. In the case of pleasure-carriages and the like, which commonly run upon good roads and depend largely for their progress upon the freedom of movement of the horse, the traces are attached in a horizontal position; fier contra, in the case of heavy vehicles and upon bad roads, an inclination of the traces is found decidedly advantageous, for not only will this disposition enable the horse to obtain a better purchase against the ground in pulling the load, but the wagon will be more easily lifted out of the ruts in the track. The average inclination for the traces may be taken at io°.
Grades.—Upon steep gradients the moving of the load becomes more difficult, for the obvious reason that the animal must partly raise his own weight in addition to that of the load. To offset this extra strain upon the horse, his speed must be lessened. It follows as a matter of course that the greater the height to be scaled, the more gentle should be the grade of the road. The best road, other things being equal, is that which has the smallest number of steep grades; for on such a road the maximum burden that may be moved on other sections will not be interfered with, since there will be no necessity to call into service the work of extra horses, which otherwise would be found necessary. The maximinn grade for stone roadways may be assumed at : 24, although for roads in mountainous reaions this rule will not hold o-ood Summary.—From all that has preceded it will be evident that in laving out a road the selection should be made of that line which is the shortest, which shall require the fewest steep grades, and which shall be so situated as to afford the best opportunity of keeping it in repair. It may not always be possible to choose the line which presents the greatest advantages from a technical point of view, in which case the rule will be modified by the pressure of circumstances.
The subject of roadways leads in natural sequence to that of railways, which will be considered in the following section.