6o THOMAS COMMERFORD MARTIN 



induction motor. To the rim of this wheel, which revolves 

 in its pit at a speed of ten revolutions per minute, are attached 

 about 550 buckets for lifting the sand from the copper ore 

 crushings. The electric sand wheel is considered to effect 

 a considerable economy over the previous methods. 



Signaling in mines requires a great variety of apparatus 

 such as telephones, telegraphs, bells, and appliances for sending 

 signals according to the indications upon a dial. Of late years 

 the telephone has gained ground rapidly over other methods 

 of signaling. Several telephone manufacturers in the United 

 States make types of telephones intended for mining work, 

 with special regard to conditions of exposure, damp, etc. 



In addition to the apparatus already described, a variety 

 of appliances are employed for counting wagons, indicating 

 the level of the water, and kindred uses. 



