October 17, 1919] 



SCIENCE 



361 



tionable wliether they ■\^^ll play more tlian 

 a minor part as compared with the steam- 

 ship, railway and motor transport. 

 . Electricity. — ^The supply and use of 

 electricity has developed rapidly in recent 

 years. For lighting it is the rival of gas, 

 though each has its advantages. As a 

 means of transmitting power over long 

 distances it has no rival, and its efficiency 

 is so high that, when generated on a large 

 scale and distributed over large areas, it 

 is a cheap and trustworthy source of power 

 for working factories, tramways, suburban 

 railways and innumerable other purposes, 

 including metallurgical and chemical proc- 

 esses. It is rapidly superseding locally 

 generated steam-power, and is a rival to 

 the small- and moderate-si/ed gas and oil 

 engines. It has made practicable the use 

 of water-power through the generation of 

 electricity in bulk at the natural falls, 

 from which the power is transmitted to the 

 consumers, sometimes at great distances. 



Fifteen years ago electricity was gen- 

 erated chiefly by large reciprocating steam- 

 engines, direct-coupled to dynamos or 

 alternators, but of late years steam tur- 

 bines have in most instances replaced 

 them, and are now exclusively used in 

 large generating stations because of their 

 smaller cost and greater economy in fuel. 

 The size of the turibines may vary from a 

 few thousand horse-power up to about 50,- 

 000 h.p. At the end of last year the 

 central electric stations in the United 

 Kingdom contained plant aggregating 

 2,750,000 kilowatts, 79 per cent, of which 

 was driven by steam turbines. 



Much discussion has taken place as to 

 the most economical size of generating 

 stations, their number, the size of the gen- 

 erating units, and the size of the area to be 

 supplied. On the one hand, a compara- 

 tively small number of very large or super- 

 stations, instead of a large number of 



moderate-sized stations dotted over the 

 area, results in a small decrease in the cost 

 of production of the electricity, because in 

 the super-stations larger and slightly more 

 economical engines are employed, while the 

 larger stations permit of higher organiza- 

 tion and more elaborate laibor-saving ap- 

 pliances. Further, if in the future the 

 recovery of the by-products of coal should 

 become a practical realization as part of 

 the process in the manufacture of the 

 electric current, the larger super-stations 

 present greater facilities than the smaller 

 stations. On the other, super-stations in- 

 volve the transmission of the electricity 

 over greater distances, and conseqiiently 

 greater capital expenditiu-e and cost of 

 maintenance of mains and transmission 

 apparatus, and greater electrical trans- 

 mission losses, while the larger generating 

 imit takes longer to overhaul or repair, 

 and consequently a larger percentage of 

 spare plant is necessary. 



The greatest element in reducing the 

 cost of electricity is the provision of a 

 good load factor; in other words, the 

 utilization of the generating plant and 

 mains to the greatest extent during the 

 twenty-four hours of each day throughout 

 the year. This is a far more important 

 consideration than the size of the station, 

 and it is secured to the best advantage in 

 most cases by a widespread network of 

 mains, supplying a diversity of consiuners 

 and users, each requiring current at differ- 

 ent times of the day. The total load of 

 each station being thus an average of the 

 individual loads of a number of consumers 

 is, in general, far less fluctuating than in 

 the case of small generating and distrib- 

 uting systems, which supply principally 

 one class of consumer — a state of affairs 

 that exists in London, for instance, at the 

 present time. It is true that there may 

 be exceptional cases, such as at Kilmar- 



