If you ever have a piece of draining to do the problem may not be so simple as this.  You may find several natural drainage areas.  Then you must lay drains through these.  Or instead of separate drains make side ones which empty into a main drain.

Going back again to the “sighting” for the drain bed level—­the boys have driven a stake into the ground.  It stands five feet above the ground level.  If a tree had been in line with the drain line this might have been used and saved driving the stakes.  Across the stake, at right angles to it, a board with a perfectly straight edge was nailed.  This board was about four feet long, one end pointed at the drain line.  At the other end Jay placed his eye looking across this to where Albert had driven stakes.

One stake had been driven into the ground at the beginning where the drain was to be dug; another at the extreme end or outlet of the drain.  Albert stood at the first stake and ran a little piece of paper slowly up and down the stake until Jay raised his hand.  This meant that the paper was on the same line with the sighting board.  Then Albert ran to the other stake and did the same.  The difference in these two points gives the difference in level of the ground.  Albert measured from the ground to his mark on the first stake, and, doing the same in the case of the other stake, found the difference to be eight inches.  This was too great a drop.  Then the boys drove two stakes in between these others and did the same work of level finding.  From stake 1 to 2, or for the first twenty-five feet there was no difference in level.  For the first fifty feet there was four inches drop; for the next twenty-five feet, 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.