RELATIONS OF ELECTRICAL ENGINEERING 611 



or motor, as laid out on paper, to as close a degree of accuracy as 

 those properties can be measured, under commercial conditions, 

 after the machine takes material form. This general precision of 

 electrical engineering has aided engineering in general to become 

 an exact science. 



Electrical engineering has adopted by international convention 

 a system of electromagnetic units which is based upon the inter- 

 national metric system, and which has the advantages of being 

 simple, decimal, and international. This has tended to give pre- 

 cision and definiteness to all electrical engineering measurements. 

 In other branches of engineering, the custom varies in different 

 countries. Thus, in hydraulic engineering, the cubic foot (of water), 

 the cubic yard, the short ton, the long ton, the metric ton, the liter, 

 the British gallon and the U. S. gallon are all promiscuously used in 

 such a manner that measurements in one country are frequently un- 

 available to engineers in other countries without lengthy arithmetical 

 reduction. This is a most unfortunate diversity. Again, in mechan- 

 ical engineering, the foot-pound-per-second, the foot-ton-per- 

 second (long and short), the British horse-power, the European 

 continental horse-power, the poncelet, and the kilogramme-meter- 

 per-second, are all in use as units of power. Unless qualified as to 

 standard geographic latitude, they are all subject to variation within 

 a quarter of one per cent above or below the mean, owing to the va- 

 riation in the force of gravitation with terrestrial latitude. On the 

 other hand, the electric unit of power, the watt, is independent of 

 the latitude, or even of the planet, and besides being an interna- 

 tional mechanical unit, is also an electrical circuit unit. For these 

 reasons the kilowatt (1000 watts or about 1 horse-power) is at 

 present steadily displacing the horse-power in engineering litera- 

 ture, all over the world. 



Electrical engineering has exercised a marked intellectual in- 

 fluence upon the time, in the direction of mathematics. Applied 

 electricity is particularly subservient to simple mathematical law, 

 which is but another way of stating that the present applications 

 of electricity are well understood. Prior to the development of 

 electrical engineering, the useful applications of mathematics to 

 engineering were almost limited to mechanics, statics, and kinetics. 

 Now, electrical engineering has thrown open to application the 

 entire stock of mathematical physics which has been accumulating 

 for several centuries. Consequently, it is now not only difficult to 

 find a department of mathematical science which does not have 

 applications useful in engineering; but engineering has also found, 

 and is constantly discovering, new fields for profitable exploration 

 by the mathematician. In the last few decades, departments of 

 mathematical analysis which had previously been regarded as 



