r's spirit-level set on an
adjustable stand will do as well. The other arm will then be a level.

Another very simple, but effective, device for finding a level line is
by means of a triangle of wood made of half-inch boards from 9 to 12
ft. long. To make the legs level, set the triangle up on fairly level
ground, suspend a plummet from the top and mark on the cross-piece where
the line touches it. Then reverse the triangle, end for end, exactly,
and mark the new line the plumb-line makes. Now make a new mark exactly
half way between the two, and when the plumb-line coincides with this,
the two legs are standing on level ground. For short water races this is
a very handy method of laying out a level line.

TO MEASURE THE HEIGHT OF A STANDING TREE

Take a stake about your own height, and walking from the butt of the
tree to what you judge to be the height of the timber portion you want,
drive your stake into the ground till the top is level with your eyes;
now lie straight out on your back, placing your feet against the stake,
and sight a point on the tree. AB equals BC. If BC is, say 40 ft., that
will be the height of your "stick of timber." Thus, much labour may be
saved in felling trees the timber portion of which may afterwards be
found to be too short for your purpose.

LEVELLING BY ANEROID BAROMETER

This should be used more for ascertaining relatively large differences
in altitudes than for purposes where any great nicety is required.
For hills under 2000 ft., the following rule will give a very close
approximation, and is easily remembered, because 55 degrees, the assumed
temperature, agrees with 55 degrees, the significant figures in the
55,000 factor, while the fractional correction contains _two fours_.

Observe the altitudes and also the temperatures on the Fahrenheit
thermometer at top and bottom respectively, of the hill, and take the
mean between them. Let B represent the mean altitude and b the mean
temperature. Then 55000 X B - b/B + b = height of the hill in feet for
the temperature of 55 degrees. Add 1/440 of this result for every degree
the mean temperature exceeds 55 degrees; or subtract as much for every
degree below 55 degrees.

TO DETERMINE HEIGHTS OF OBJECTS

_By Shadows_

Set up vertically a stick of known length, and measure the length of its
shadow upon a horizontal or other plane; measure also the length of
the shadow thrown by the object whose height is required. Then it will
be:-