230 MOTIVE POWER EMPLOYED

when treating on the loco-motive engine,enlarge a little more upon the effect of this,in diminishing the performance of these kindof engines.

Ill—HORSES.

The power of a horse, or that part of hismuscular exertion, which, in travelling, he iscapable of applying upon the load, has beenvariously stated by different authors. It is notthe force he is capable of exerting at a deadpull, or for a short period, by which we arcto judge of, or estimate, his strength ; it iswhat he can exert daily, and day after dayfor a long period, without injury to his phy-sical powers, that we are to take as thecriterion for practice.

A Rail-road is peculiarly adapted to showthe power of a horse, as he is continuallyemployed in overcoming the same resistance,

and the inclination of tho road in general has

little effect upon the power required to over-come the gravity of his own weight.

The following Tables will show differentRail-roads, where horses have been used forsome years, and the respective resistanceswhich the inclination of the road and thefriction of the carriages presented to the actionof the horse.