Milford chronicle., 1915-07-16

you will see these circles we have drawn
one inside the other. Draw them on a
map and you would have the exact rep
resentation of the contour of the hill.
This is the way hills are represented on
a map. of course, no hills are in the
shape of an exact cone, and these lines
showing the contour instead of being
circles one inside the other and the same
distance apart at all points are irregular
in shape and are closer together as the
hill is sleeper aud further apart as the
slope is more gradual. The distance be-
tween these lines showing the contour is
called the vertical interval II is usually |
abbreviated as V. l. 1t may be taken |
any number of feet desired when draw
ing the map. The V. l. is always marked |
on the map so that any one who reads
it may be able to tell the height of the
different elevations. 1t is usual so mark
the elevation above sea level on every
fifth contour line. The contour lines of
course connect all points on the hill which
have the same elevation. On the United
States Geological Survey, the vertical in
terval or contour interval, as it is also
called, is twenty feet. In sketch maps,
however the V. l. usually varies accord
ing to the scale of the map. The follow
ing is the best usage Scale 3 inches to
the mile, V. l. 20 feet; inches to the
mile, V. 1. 10 feet; II inches to the mile,
V. 1. 5 feet. Remember now that the
V. I. means the vertical distance between
the contours. The horizontal distances
between them depends of course on how
steep the slope is. If the elevation was
straight up and down, as for instance in
the case of a cliff, the horizontal distance
would be zero and the contour lines
would all coincide or run together at that
point. As the slope gets more gradual,
he horizontal distance between contonrs
gets greater and greater. This horizon
al distance is usually called map dis
ance. Now we have that for every de-
5ree of slope, we will get a rise Tor fall)
# one foot in a horizontal diatance of
2 $40 feet. So if we can determine the
ngle of elevation or of depression, we
an readily figure out the height of the
i'll. To get this angle, we can devise a
ope board out of our drawing board.
asteu a small weight to one end of a l.
iece of string and attach the other end =
, the middle of one edge of the drawing -
)ard. Now if the board is held with L
lis edge perfectly level, the string with
lie weight on will hang perpendicularly
I'd line drawn along it will divide the
,ard in two Mark off on this line,
7-l0 inches from the top, and to this
lint draw the arc of circle, using 5 7-10
ches as the radius. Mark where the
rye crosses the perpendicular line as
70. Divide the arc into divisions of
e-tenth of an inch each. Each division
II register one degree. Sight along the
p edge of the board at the object whose
evation you wish to get, aiming at a
int as high above the object as your
E is approximately above the ground
lere you are standing. Hold the string
it hangs and read how many degrees
registered by the pendulum. Away
IN you, of course, registers a depres- y
n and towards you an elevation. Now Y
one degree of elevation means a rise
one foot in 81 $40 feet, horizontal
tance to get a rise of 20 feet there
uld have to be a horizontal distance
ll46 feet. Five degrees of elevation
uld give rise of 20 feet in one-fifth
this oa 2202 feet. On the map if the
le was three inches, one mile, and our
l. 20 feet we would have to mark off
Ontour every thirteen hundredths of -
inch on hill that had five degrees
'ation. 1922 feet equals 1750.4 in
5. Divide $500 inches lone mile)
three and we get 2112O. Divide
O.4 inches by 2ll20 and we get is
hes
Continued next week.)