Another mode of levelling, by means of a mammoth mason's level, with an improvement, was invented by Colonel Challoner, and published in the Journal of the Royal Agricultural Society. It may appear to some persons more simple than the span level. We give the cut and explanation.
"I first ascertain what amount of fall I can obtain, from the head of every drain to my outfall. Suppose the length of the drain to be 96 yards, and I find I have a fall of two feet, that gives me a fall of a quarter of an inch in every yard. I take a common bricklayer's level 12 feet long, to the bottom of which I attach, with screws, a piece of wood the whole length, one inch wider at one end than at the other, thereby throwing the level one inch out of the true horizontal line. When the drain has got to its proper depth at the outfall, I apply the broadest end of the level to the mouth; and when the plumb-bob indicates the level to be correct, the one-inch fall has been gained in the four yards, and so on. I keep testing the drain as it is dug, quite up to the head, when an unbroken, even, and continuous fall of two feet in the whole 96 yards has been obtained."
Fig. 60.—Challoner's Level.
SPADES AND SHOVELS.
Fig. 61, 62, 63.—Drain Spades.
No peculiar tool is essential in opening that part of the drain which is more than a foot in width. Shovels and spades, of the forms usually found upon well-furnished farms, and adapted to its soil, will be found sufficient. A Boston agricultural house, a year or two since, sent out an order to London for a complete set of draining tools. In due season, they received, in compliance with their order, three spades of different width, like those represented in the cut.