Greene County herald. (Leakesville, Miss.) 1898-current, 1901-05-03

God Roads R00tss


advance of community in wealth. II
is eXtrayagant to build a road with q
surface costly enough for heavy haul.
ing, but with grades too steep for any
but the lighter loads. To harmonic is
to economize. So it is worth while to
seek for harmony between the grade
and surface of road. In this inquiry
hair-splitting accuracy, which interests
nobody but the theorist, will be avoid
ed. And, as becomes serious men in
considering an important subject. nc
greater accuracy will be INDUCED in
than has to do with dollars and cents.
How hard pull horse should deliver
to his traces depends on the horse him
self, on the speed and ON the length of
time he works. For heavy hauling the
speed must, Of course, be a moderate
walk. The average horse in this south
ern country cannot deliver pull of
more than ninety pounds to his traces
for any considerable time even at a
walk without hurtful over exertion.
Thus $50 pounds is quite as much of a
pull as should regularly be required
of an ordinary pair of horses in the
South. But it must be noticed that
this is the pull on the traces and not
the weight of the load
| Next 1t must be observed that the
pull needed to draw a given load de-
ponds on the grade and on the road
way; for we shall tacitly ascribe to the
last or ignore resistances from other
sources. The roadway always opposes
the motion, whether up hill, down hill
or on level, with a force of so many
pounds per ton of gross load hauled
The amount of pull thus exacted de-
ponds on the character and condition
of the roadway. Practically it is not
affected by any ordinary grades. While
ascending the horses must exert the
pulls called for by both roadway and
grade. Thus, sand roadway calls for
400 pounds per ton, while steel calls
for ten. A twenty per cent grade
calls for 392 pounds. Hence the pull
needed to draw one ton up such a
grade is 792 lounds on sand but 400
on steel. In the same way it may be
seen that pulls of AGO and seventy
pounds, respectively, are needed in as
cendiDg three per cent grade on
sand and steel.
Now notice what these figures mean
On level a horse can draw forty
times as much on steel as on sand: on
a three per cent. grade less than seven
times as much; on a nine per cent.
grade about three times; while on
twenty per cent. grade barely two
times as much. If we compare steel
with macadam we shall see that on a
level horse can draw six times as
much on steel as on macadam; on a
three per cent. grade one and three
fourth times as much, while on n nine
per cent. grade only one and one
fourth as much. Thus a road of high
class has little advantage over one of
lower class if the grades are heavy.
AS already pointed ont the pull of the
team, while ascending, is divided into
two distinct parts. The part spent in
overcoming the resistance of the road
way Is entirely lost. But the part that
overcomes the downward pull of the
in accommodating work for future use.
The amount of this last per ton of
load is a definite quantity for any
given vertical ascent, and cannot be
increased or diminished in any way
whatever. Every bit of 1t is recovered
on the descent, as we shall see. If not
recovered too fast it all goes to reliev-
| ff.fr fIn
the excess is wasted by the brake, or
the team has to undo it by the addi,
tional work of holding back. In the
descent the grade pulls forward and
the roadway holds back with the
amounts per ton of load already point
ed out. So long as the pull of the
grade does not exceed the resistance
of the roadway there is no waste. The
team pulls with q force equal to the
| difference and gets more or less of re-
3ef at every step. But when the
grade pulls harder than just enough to
overcome the resistance of the road
way the brake must be used or the
team must hold back and waste re-
suits. This shows that there should
be definite limit. different for each
kind of roadway, to the steepness of a
grade. Thus for sand, which offers a
resistance of 400 pounds per ton, a
twenty per cent. grade, which pulls
with 392 pounds, is somewhat below
the limit. But such a grade ON steel.
which only opposes ten pounds, would
give an excess of 1913 pounds, to be
wasted by the brake. One-half of one
per cent. is the limit for the grade on
steel. Extending the examination to
the other roadways we see that to
avoid waste on the descent no grade
should be sleeper than twenty about,
nine, three or one-half per cent, re-
spectively, on sand, dirt, macadam or
steel roadway. 1t now remains to see
whether conditions connected with the
ascent demand the lowering of these
limits. In the first inquiry we had for
guidance the well-known facts from
mechanics and figures from the dyna-
mometer. But in this second inquiry
we must be guided also by human
judgment. But this is based on much
experience and is singular in its una