t to the
mile, he can draw only one-half as much, and on a ten per cent grade, or
520 feet to the mile, he is able to draw only one-fourth as much as on a
level road.

As a chain is no stronger than its weakest link, just so the greatest
load which can be hauled over a road is the load which can be hauled
through the deepest mud hole or up the steepest hill on that road. The
cost of haulage is, therefore, necessarily increased in proportion to
the roughness of the surface or steepness of the grade. It costs one and
one-half times as much to haul over a road having a five per cent grade
and three times as much over one having a ten per cent grade as on a
level road. As a perfectly level road can seldom be had, it is well to
know the steepest allowable grade. If the hill be one of great length,
it is sometimes best to have the lowest part steepest, upon which the
horse is capable of exerting his full strength, and to make the slope
more gentle toward the summit, to correspond with the continually
decreasing strength of the fatigued animal.

So far as descent is concerned, a road should not be so steep that the
wagons and carriages cannot be drawn down it with perfect ease and
safety. Sir Henry Parnell considered that when the grade was no greater
than one foot in thirty-five feet, vehicles could be drawn down it at a
speed of twelve miles an hour with perfect safety. Gillespie says:

"It has been ascertained that a horse can for a short time double his
usual exertion; also, that on the best roads he exerts a pressure
against his collar of about one thirty-fifth of the load. If he can
double his exertion for a time, he can pull one thirty-fifth more, and
the slope which would force him to lift that proportion would be, as
seen from the above table, one of one in thirty-five, or about a three
per cent grade. On this slope, however, he would be compelled to double
his ordinary exertion to draw a full load, and it would therefore be the
maximum grade." Mr. Isaac B. Potter, an eminent authority upon roads,
says:

"Dirty water and watery dirt make bad going, and mud is the greatest
obstacle to the travel and traffic of the farmer. Mud is a mixture of
dirt and water. The dirt is always to be found in the roadway, and the
water, which comes in rain, snow, and frost, softens it; horses and
wagons and narrow wheel tires knead it and mix it, and it soon gets into
so bad a condition that a fairly loaded wagon cannot be hauled thr