Engineering Wonders of the World
Volume III

ARTESIAN WELLS, AND HOW THEY ARE BORED. 341 the size of the lining tube to see if it is of a suitable size, and is then lowered down the bore - hole beyond the up- standing end of the broken rod and past the first joint. A rotation of the crow’s foot causes it to grip the broken rod, which is then hauled up. Sometimes the operation is not so straightforward, for th© tools at the lower end of the broken rods may become set fast by grit settling round them. Circular tools and shell pumps are very liable to be stuck fast by such gritty sedi- ment, and it is an axiom with well-borers never to leave a tool at rest at the bottom A DANDO ” SAND SCREEN BELT. This is a brass cylinder with vertical V slo's cut frcm the inside. The point of the \ just comes through the outbids wall, forming a mere slit. Water has the property of flowing freely through a slit so narrow as to exclude even fine sand. of a hole, but always to draw it up fifteen or twenty feet so as to be out of the region of sediment. Powerful hydraulic jacks often fail to extract such stick-fasts.” Sometimes the rods are pulled apart by the stress, and breakdowns, perhaps three deep, are piled one above another in a narrow bore- hole. As a last resource for dealing with a hopeless stick- fast, dynamite, or some other explosive, is used. A charge of a few pounds of Explosives. high explosive detonated at the bottom of a bore-hole will sometimes blow all obstruc- tions into the sides of the hole, and allow the lining pipe to be forced down past the spot. Explosives are often employed also to make a bore-hole yield a better sup- ply. It may happen that the hole has traversed no fissure, and yields but little water. A “ shot ” may fracture the rock through to some fissure, and make a passage by which water can reach the boring. Such shots are by no means always successful. WATER GUSHING FROM A WELL AT SLOUGH JUST AFTER STRIKING THE GREENSAND. The output is 100,000 gallons per hour. The large horizontal bevel wheel in the centre is driven by steam to revolve the tools. {Photo, by courtesy of Messrs. C. Isler and Co.)