WELLS AND WELL SINKING. 45 



trated and described. Tools employed for simple 

 boring are however different, and they are of course 

 confined to use in soft ground. For use in stiff 

 clay the form shown by fig. 36 is generally employed, 

 while for running sand, in order to prevent a return 

 of the spoil, the type shown in fig. 37 must be used. 

 It has two flap (or clack) valves as shown. The 

 rods used for working these augers must have 

 guides attached to them, being a loose running fit in 

 the guide tubes. 



It may have been mentioned that when an artesian 

 well has been cut in rock, and water is found but 

 only percolates slowly, a decided improvement can 

 often be made by exploding a charge of nitro- 

 glycerine in the bottom of it. This charge consists 

 of a sort of torpedo made of tin and filled with the 

 required quantity of nitro-glycerine, and having a 

 detonator and fuse. The former consists of a 

 copper capsule filled with fulminate of mercury, 

 while the safety fuse is inserted into the open end 

 of the detonator until it reaches the 

 fulminate, and the copper casing pressed 

 round the wire to close it up. The 

 idea is shown by fig. 38. The whole 

 detonator is then pushed home into the 

 primer, and connected to an electro- 

 magnetic machine or low tension bat- 

 tery at the surface, the top of the de- 

 tonator having been made quite water- 

 tight with beeswax beforehand. The 

 wires for the electric current to travel 

 along must of course be thoroughly well insulated 

 and waterproofed. These detonators want great 



