Applied Science 803 



mission due to the resistance of a conductor decreases rapidly 

 with increase in pressure; or, to state the facts differently, the 

 higher the pressure the smaller may be the conductor for an equal 

 loss. The cost of conductors is a very heavy item, so pressures 

 have been raised again and again with increase in distance of 

 transmission. Twenty years ago 50,000 volts was considered a 

 very high pressure; to-day lines are carrying current at 220,000 

 volts, and electricians look forward to much higher voltages still. 

 After leaving the step-up transformers, the long-distance 

 current flashes through insulated wires or cables, slung aloft on 

 poles and trestles, and after a journey over, maybe, rivers, moun- 

 tain passes and gorges, prairies and deserts, reaches the far-away 

 station where it is to be distributed. Before admission to the 

 switchboard it has its pressure reduced, by step-down transform- 

 ers, to a suitable level. The switchboard divides it among a number 

 of different circuits. Some may be sent to sub-stations, where it is 

 converted into continuous current for operating tramways and 

 suburban railways. (Machines of the kind which effect this con- 

 version may be heard buzzing in annexes to some of our tube 

 stations.) Other circuits supply power for running factories; 

 and others again, through small transformers dotted about over 

 the area served, energy for lighting and heating. At any of its 

 many final destinations the current may of course be passed 

 through apparatus to suit it for any special purpose. 



3 



The Storage of Electricity 



The only method yet discovered of storing electrical energy 

 in commercial quantities involves the use of accumulators or 

 . storage batteries, subdivided into a number of cells. In a cell 

 are a number of plates or elements charged with chemicals and 

 submerged in a liquid called electrolyte. The plates are inter- 

 connected to form two groups, those of one group alternating 

 with those of the other group ; and each group is connected with 



