Artesian Wells. 393 



^Yorking of those appliances. Boring is usually continued some 

 distance below the point where the water is tapped, in order to 

 strengthen the supply, and the pump cylinders are placed well below 

 the rest level of the water to allow for lowering this level by pumping. 

 Exhaustive tests of these water supplies are made, and the effect on 

 the surface level and the quality of the water are carefully recorded, 

 and sections of all bores, with core samples of each of the strata 

 passed through, are preser\-ed for future reference. 



METHODS OF EORIXG. 



There are two principal methods of drilling vertical holes into 

 the crust of the earth, the (jne more suitable for boring in certain 

 formations or under particular conditions than the other. The older 

 of these methods is what is called the " percussion system," known 

 and extensively used in a primitive form in the East long before it 

 reached Europe in the twelfth centurx. The essential feature of the 

 machine employed in boring on this system is a heavy steel chisel, 

 susp>endej, with weighting and turning attachments, by a rope or 

 line of rods from a derrick above the ground, which is raised and let 

 fall by mechanical means, so that the steel tool cuts and pulverises 

 the rock it acts on at the bottom of the hole, and with the assistance 

 of water ptjured in gradually extends the hole downwards. The de- 

 bris thus detached is brought up by introducing a hollow cylinder, 

 with a hinged valve at the bottom opening upwards, which fills with 

 sludge and is drawn up. The chisel is then put to work again. This 

 kind of boring plant works quickly and economically in the softer 

 formations, but when the rock becomes hard a more effective machine 

 is the diamond drill, introduced about thirty years ago. The active 

 principle of this machine is quite different from that of the one first 

 described, as by this method a rapidly revolved tool, pointed with 

 diamonds, cuts away and abrades the rocks, penetrating gradually 

 downwards, leaving a smooth, clean hole. As the cutting edge of the 

 tool is annular, it cuts a clear space on the outer part of the hole and 

 leaves a central core, which is taken out as the work proceeds, while 

 water under pressure is pumped down the centre of the hollow boring 

 rods, which rotate the diamond cutter, and returns to the surface 

 outside them, having flushed the cutting tool, bringing the debris 

 with it. In some cases, however, boreholes are of a loose and soft 

 material in one part, in another of verj- hard rock, and it is necessary 

 to employ both systems of drilling. This difficulty is overcome by 

 fitting some boring machines with a combination of both methods, 

 so that alternate layers of soft and hard material can be dealt with 

 with equal facility. 



A quantity of water is absolutely necessary for boring, besides 

 that required for the boiler of a steam-power machine, and this varies 

 from 50 to 200 gallons a day for drilling purposes, and from 100 to 

 300 gallons a day for the boiler, according to the class of machine 

 employed. 



