Steam and electric automobiles do tire,—­that is, long pulls through heavy roads or up grades tell on them,—­the former has trouble in keeping up steam, the latter rapidly consumes its store of electricity.  The gasoline machine does not tire.  Within its limitations it can keep going indefinitely, and it is immaterial whether it is up or down grade—­save in the time made; it will go all day through deep mud, or up steep hills, quite as smoothly, though by no means so fast, as on the level; but let it come to one hole, spot, or hill that is just beyond the limit of its power, and it is stuck; it has no reserve force to draw upon.  The steam machine can stop a moment, accumulate two or three hundred pounds of steam, open the throttle and, for a few moments, exert twice its normal energy to get out of the difficulty.

It is not a series of hills that deters the gasoline operator, but the one hill, the one grade, the one bad place, which is just beyond the power he has available.  The road the farmer calls good may have that one bad place or hill in it, and must therefore be avoided.  The road that is pronounced bad may be, every foot of it, well within the power of the machine, and is therefore the road to take.

In actual road work the term “horse-power” is very misleading.

When steam-engines in early days began to take the place of horses, they were rated as so many horse-power according to the number of horses they displaced.  It then became important to find out what was the power of the horse.  Observing the strong dray horses used by the London breweries, Watt found that a horse could go two and one-half miles per hour and at the same time raise a weight of one hundred and fifty pounds suspended by a rope over a pulley; this is equivalent to thirty-three thousand pounds raised one foot in one minute, which is said to be one horse-power.

No horse, of course, could raise thirty-three thousand pounds a foot or any portion of a foot in a minute or an hour, but the horse can travel at the rate of two and one-half miles an hour raising a weight of one hundred and fifty pounds, and the horse can do more; while it cannot move so heavy a weight as thirty-three thousand pounds, it can in an emergency and by sudden strain move much more than one hundred and fifty pounds; with good foothold it can pull more than its own weight along a road, out of a hole, or up a hill.  It could not lift or pull so great a weight very far; in fact, no farther than the equivalent of approximately thirty-three thousand pounds raised one foot in one minute; but for the few seconds necessary a very great amount of energy is at the command of the driver of the horse.  Hence eight horses, or even four, or two can do things on the road that an eight horse-power gasoline machine cannot do; for the gasoline machine cannot concentrate all its power into the exertion of a few moments.  If it is capable of lifting a given load up a given grade at a certain speed on its lowest gear, it cannot lift twice the load up the same grade, or the same load up a steeper grade in double the time, for its resources are exhausted when the limit of the power developed through the lowest gear is reached.  The grade may be only a mud hole, out of which the rear wheels have to rise only two feet to be free, but it is as fatal to progress as a hill a mile long.