five inches rise; and the last twenty-five feet, six inches drop. They
marked all this on the stakes in order to make sure they got the level
right. The bed must, you see, drop one inch for every twenty-five feet.
For the first fifty feet of the line the drop was just twice too much;
then came the abrupt rise and drop.

Albert ploughed a furrow straight along the line and ploughed back
again. Then he reploughed. The boys then began to dig, making a ditch
three feet deep right through the land. In order to get the right level
they used a home-made device and plumb-line which can be made as
follows: Nail the ends of two six-inch boards ten feet long, so as to
make a right angle; then across the open end of the triangle, nail
another six-inch board having the lower edge about a foot from the ends
of the boards. Cut off the ends of the boards on a level, so that they
will rest evenly on the ground. Next drive a nail into the apex of the
triangle, and to it tie a line long enough so that when the triangle is
stood on its legs, the plumb-bob, which you will tie on the other end of
it, will almost reach the ground.

The centre must next be determined. To do it, set the triangle up on its
legs on a level place and when the plumb-line comes to rest, mark the
place. A lead-pencil mark will do, but as it is liable to become
obliterated by the dirt, a saw mark is more permanent.

Now you know what the grade of the bottom of your ditch will be.
Reproduce this on a level place by means of a board with a large enough
block under one end to give the right pitch; put the triangle on this
and when the plumb-line comes to a rest, mark the place on the cross
piece. Reverse the ends of the triangle to get a similar mark on the
other side of the centre or level mark. This makes a level by which a