Power and Speed bear a certain relation one to another. It has been long and well known that no horse can exert all his speed and all his strength at the same moment; as we increase the pace beyond a certain point, we must reduce the load; that as we reduce the load we may increase the pace; and that as we increase the demand, either for power or for speed, we must shorten the duration of labor. These are general principles, applicable to all kinds of horses, and to all kinds of work, at least to all work that deserves the name of labor.

Various experiments, chiefly in relation to drawing, have been made for the purpose of ascertaining in what degree power and duration decline as the volocity rises. But the strength and the speed vary so much in different horses, and even in the same horse at different times, that an approximation to the relation which one bears to another, is all that can be obtained or expected. The power of a horse is estimated by the load he can draw or carry a given distance in a given time. In drawing it has been stated as equal to a force of 160 pounds, the pace being about 2½ miles per hour. Some experimentalists have rated it at only 112, others so high as 193, the pace being the same. But horses are so different that hardly two experiments can yield precisely the same results. The following table was constructed to show the rate at which power and dura tion decline as the pace is raised, but it seems of no use except to illustrate the general principle.

In the table opposite will be found a statement of work at different paces. The table is not so complete as I wish, but so far as it goes it shows the amount of work actually performed. The weight of the load is stated at the highest, but on many days it may be considerably lighter, especially in stagecoaches.