72 G

THEORY AND PRACTICE OF ENGINEERING.

Book II.

press them against the outside uprights, held together by the cords at their upper ends ;between each pair of uprights it is found necessary to have a strut or one of these sticks;when placed, the cords above are tightened by twisting them with a small piece of wood

Fig. 605.

P1SB-WORK

introduced between them. When the frames are thus fixed, the earth is thrown in, andworked in the same manner as concrete or common mortar ; first well wetting the partsabout the putlocks, to enable their being easily withdrawn ; as many workmen are then em-ployed as there are divisions, one being placed in each compartment.

After the bottom is well-cleaned and lightly sprinkled with water, the labourers bring tothe masons the prepared earth in wicker baskets, and tread it with their feet so as to form abed of an uniform thickness of not more than 3 or 4 inches; they then ram it down, reducingit to little less than half its former thickness ; this first bed being compressed, the labourersbring more earth, and form another, spread out and beat in the same manner, and so on tillthe whole case is filled.

The rammer is a block of wood 10 inches high ; at the middle of its height it is square,and 6 inches by 5, diminishing in thickness, and terminated by rounded edges at the bot-tom : towards the upper part it is terminated by a circular surface 4 inches in diameter,in the centre of which a hole is sunk 1 inch in diameter and 2 inches deep; the circularpart at the top being rounded off from the square below, the flat portion of the rammerat bottom must be perfectly smooth and even ; a block of ash, elm, or hazel, is usually pre-ferred ; the handle is 4 feet 2 inches long, and in ramming it is turned round at each stroketo make the w r ork solid and to unite it with that previously done.

When a wall is commenced, the first frame is put at one of its extremities, and the end isinclosed by two planks united by cleets, secured at the top by two iron cramps ; the otherpart, where there is no end, is terminated by a fall of about 60°. The section of the wallserves to unite the first constructed with that which follows.