ELECTRICITY IN MINING 41 



Colgate to Oakland, where the Bay Counties company's line 

 ends, is a distance of 152 miles; from Oakland to San Fran- 

 cisco, by the Standard company's line, is 70 miles. The tjan^r; 

 in at Oakland thus gives a transmission circuit of 232 miles 

 from the latest plant at De Sabla, beyond Colgate, around San 

 Francisco bay and through San Jose to San Francisco. Over 

 the network thus represented, which embraces no fewer than 

 16 counties, within whose borders lie one half of the popula- 

 tion and three fourths of the total assessed valuation of prop- 

 erty of the state, several thousand horsepower is delivered 

 daily. Alternating current is distributed to substations at 

 pressures of 40,000 to 60,000 volts and there manipulated and 

 rectified for delivery to establishments engaged in a variety 

 of industries, including a large number of mining plants. 



Electric coal cutters constitute one of the largest classes 

 of mining machinery employing electric current. The con- 

 siderable increase during recent years in the proportion of 

 machine mining as compared with that of pick mining is 

 doubtless due to the adoption of these machines. 



The older form of machine is of the pick or puncher t3^e 

 run by compressed air, but of late j^ears the chain form driven 

 by electricity has rapidly come into use. Some interesting 

 details with regard to the introduction and utilization of elec- 

 tric coal cutting machinery were recently made public by 

 Mr. S. B. Belden, who is connected with one of the largest con- 

 cerns manufacturing such apparatus. Speaking of the first 

 chain machines, designed b}" Mr. J. H. Jeffrey, Mr. Belden 

 stated that their height precluded the possibility of operating 

 them in thin coal, and that for several years no attempt was 

 made to build a machine designed specially for such work. 

 Even when the chain machine was an established success, it 

 was a question whether a machine weighing more than a ton 

 could be employed in coal ranging between 32 and 36 inches 

 in thickness. But after these large machines had proved 

 successful in thick veins they began to be used in lower coal 

 imtil the minimum thickness of the vein had been reached. 



Gradual evolution has produced a smaller and lighter 

 machine, so that there is now in use one which has a lieiglit of 

 only 18 inches, or, with the moving truck, of 28 inches, and a 



