Fig. 38.—Double-grooved ground-surface.
A Rodway shoe has two longitudinal grooves and three ridges on its ground-surface. The outer groove carries the nails, and the inner groove lightens the shoe and increases the foot-hold. It is not the number of grooves or ridges that prevents slipping; it is the absence of a continuous flat surface of iron, and the existence of irregularities which become filled up with sand and grit. A four-grooved shoe has no more anti-slipping properties than a three-grooved, and a one-grooved shoe is as good as either, although it cannot stand the same amount of wear.
Transverse ridges and notches have also been tried as ground-surfaces for shoes, but offer very little, if any, better grip than the longitudinal grooves. Their great disadvantage is that they cannot be made deep enough without weakening the shoe, whilst if shallow they are worn out before the shoe has been long in wear.
Fig. 38.—Ground-surfaces, notches, projections, ridges.
A Calkin is the name given to the extremity of a shoe when turned down at the heels. Calkins are used on most hind shoes and, in some parts of the country, on fore shoes. They are supposed to be the most convenient and effective means of giving good foot-hold. This supposition is correct when a horse travels on soft ground or on streets so paved that a space is left between each course of stones. They are of very little use on asphalte or wood pavement, and not much more use on roller-made macadam. With light modern carriages and level modern roads calkins are quite unnecessary, and better means of giving foot-hold may be substituted. It is a fact that horses when shoes are new and calkins prominent do their work without slipping, and that when the calkins are worn down the horse moves with less confidence and security. This does not prove that calkins are necessary. It must be remembered that horses possess a power of adapting themselves to circumstances, but having learned to rely upon any artificial assistance they are the more helpless, for a time, on its withdrawal. Calkins assist the horse for a time, but after the calkin is worn down the horse is in a worse position than if he had never become accustomed to its assistance. Of course on soft ground, especially grass, calkins afford a firmer grip than any other contrivance. On the other hand, their constant use lifts the frog out of bearing and causes it to waste, thus spoiling the action of the natural provision against slipping. Level shoes on the hind feet promote sound, prominent frogs, and give firm foot-hold for all light horses. Even omnibus horses, now that the vehicles are supplied with effective foot-brakes, may advantageously be worked without calkins. On country roads, especially when the district is hilly or the load is heavy, calkins may be requisite, and must then be made to do as little harm as possible.
