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From an issue of Vick's Monthly Magazine from the 1880s
The height of a tree may be estimated sufficiently exact for
ordinary purposes by the following method:
Being in the neighborhood of a tree, the height of which you wish
to know, and in your hand you carry a walking cane, or a jointed
fishing rod, and supposing the cane, or a length of the rod, is
three feet, set it in the ground perpendicularly and, if the sun
shines, it will cast a shadow; now, with a pocket rule, you
measure the length of the shadow, and find it, say two feet. Here,
then, we have a right angle of two feet and three feet. Now,
supposing the tree to be tolerably straight, measure from its base
to the end of its shadow, and we will suppose it to be twenty
feet. Now, if a cane three feet high casts a shadow of two feet,
how high must a tree be to cast a shadow of twenty feet? Or, in
other words, if two gives three, how much twenty feet give?
But suppose the sun don't shine, what then? Why, then set up the
cane as before, say eighteen feet from the base of the tree. Now,
place your head on the ground, with the cane between you and the
tree, moving nearer to or further from it, until you can just see
the top of the tree over the top of the cane; place a pebble or
mark on the ground at the point where you obtain this view. The
cane being three feet high, the distance from the pebble to it
will be two feet; hence, by the same rule, we ascertain the height
of the tree to be thirty feet.
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