132 SECTIONAL ADDRESSES 



Already electrical appliances have pervaded every field of mechanical 

 engineering. The electrical driving of factories has become so general 

 as greatly to reduce the smoke and vi^aste of factory chimneys. The very 

 heaviest kinds of machinery, such as the rolling-mills for rolling boiler- 

 plate and rails, are now driven electrically. Some of the rolls call for 

 loads of 10,000 h.p. at times of peak load. In our mines electricity is 

 becoming more and more vi^idely used for driving coal-cutters and 

 conveyors, as weW as for hauling and winding. In the deposition 

 and refinement of metals, electrical processes are all-important. The 

 electric furnace is the most perfect one for the treatment of 

 metals at high temperatures. The electrical equipment of motor- 

 cars has become an important industry in itself, employing millions 

 of capital. 



One of the directions in which rapid strides will be made in the near 

 future is in connection with electric transmission. Following fast on the 

 construction of the national 132,000-volt lines and the Weir Report, 

 which showed what economies might be effected by the electrification of 

 our railways, comes the wonderful development made possible by the 

 grid-controlled mercury-vapour arc. The mercury-vapour arc (which 

 for some years has been capable of carrying thousands of amperes) is now 

 provided with a grid much in the same way as a trinode valve in a wireless 

 set. Make the grid negative and no current will flow either way ; make 

 it positive and the arc acts as an ordinary valve. Thus, by connecting 

 two grids to an alternating voltage, a pair of valves will deliver alternating 

 current from a direct-current source. This makes possible the trans- 

 mission of power at a B.C. pressure of 180,000 volts easier than when 

 A.C. is used at 130,000 volts. It does away with many difficulties due 

 to capacitance and inductance. 



Another application of this device is to change a power supply from one 

 frequency to another. It is possible to take power from a single-phase 

 trolley line and convert it into three-phase power at any frequency, so 

 that three-phase motors can be started at a low frequency and the number 

 of cycles per second can be increased as the speed of the train rises. 

 Moreover, the voltage can be regulated over a wide range without the 

 necessity of transformer taps. There are also great facilities for arresting 

 the current on an accidental short circuit. This revolutionises the possi- 

 bilities with polyphase traction and gives it some advantages over D.C. 

 traction which were quite unexpected a year or two ago. 



But there is yet another surprising improvement in electric traction 

 along entirely different lines. The Drumm storage battery employed 

 in the Great Southern Railway of Ireland has shown such remarkable 

 characteristics as a traction battery that it has revived the hope held by 

 many of us that some method of storing electrical energy could be found 

 which would make the electric locomotive independent of any connection 

 to a trolley. If it be possible to build powerful, efficient electric loco- 

 motives independent of any connection to an external system, and capable 

 of long journeys without recharging, it is obvious that they would provide 

 a more desirable method of electric traction than that generally adopted 

 at present for main lines. Battery-fed shunting locomotives are already 



