In the ordinary system of well boring, innumerable breakages and delays occur when a boring is required to be carried to any depth exceeding 200 or 300 feet, owing to the buckling of the rods, the crystallization of the iron by the constant jarring at each blow, and particularly the increased weight of the rods as the hole gets deeper. It follows from this, that where the excavation is very deep, there is considerable difficulty in transmitting the blow of the tool, in consequence of the vibration produced in the long rod, or in consequence of the torsion; and, for the same reason, there is a danger of the blows not being equally delivered at the bottom. It has been attempted to obviate this difficulty, but without much success, by the use of hollow rods, presenting greater sectional area than was absolutely necessary for the particular case, in order to increase their lateral resistance to the blows tending to produce vibration. Boring is usually executed by contract. The approximate average cost in England may be taken at 1_s._ 3_d._ a foot for the first 30 feet; 2_s._ 6_d._ a foot for the second 30 feet; and continue in arithmetical progression, advancing 1_s._ 3_d._ a foot for every additional 30 feet in depth. This does not include the cost of tubing, conveyance of plant and tools, professional superintendence, or working in rock of unusual hardness, such as hard limestone and whinstone. A clause is usually inserted in the contract, to the effect that, if any unforeseen difficulty is met with in the course of the work, it is then paid for by the day, at a rate previously determined upon, until the difficulty has been overcome. CHAPTER V. AMERICAN TUBE WELL. This well consists of a hollow wrought-iron tube about 1-3/4 inch diameter, composed of any number of lengths from 3 to 11 feet, according to the depth required. The water is admitted into the tube through a series of holes, which extend up the lowest length to a height of 2-1/2 feet from the bottom. The position for a well having been selected, a vertical hole is made in the ground with a crowbar to a convenient depth; the well tube _a_, having the clamp _d_, monkey _c_, and pulleys _b_, Fig. 95, previously fixed on it, is inserted into this hole. The clamp is then screwed firmly on to the tube from 18 inches to 2 feet from the ground, as the soil is either difficult or easy; each bolt being tightened equally, so as not to indent the tube. The pulleys are next clamped on to the tube at a height of about 6 or 7 feet from the ground, the ropes from the monkey having been previously rove through them. [Illustration: Tube Well Assembly. Fig. 95.]