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ELECTRICITY. — The international system of electric and magnetic 

 units. J. H. Dellinger. Bureau of Standards Scientific Paper 

 No. 292 (Bull. Bur. Stds., 13: 599-631). 1916. 

 A complete and distinct system of electric and magnetic units is in 

 use, based on the international ohm and ampere, the centimeter, and the 

 second. While these international units differ in their derivation from 

 the electrostatic and electromagnetic units, they nevertheless repre- 

 sent very closely decimal multiples and submultiples of the theoretical 

 electromagnetic units. The very slight differences are determined by 

 absolute measurements made from time to time. One of the reasons why 

 the international system is the most convenient and the most used elec- 

 trical system is because it is centered around the phenomena of electric 

 current. Electric current is more familiar and of vastly greater practi- 

 cal importance than electrostatic charges or magnetic poles, upon which 

 the other two familiar systems are based. Another fortunate aspect of 

 the international system is the convenience of its dimensional expres- 

 sions. They are very simple, and directly suggest the ordinary rela- 

 tions of electrical theory and practice. Other systems, involving the 

 definition of new units of certain quantities in such a way as to redis- 

 tribute the factor 4x in the equations, have been proposed from time 

 to time and some of these are now used to a limited extent. An attempt 

 to redistribute the 47r's in an advantageous manner has been called a 

 "rationalization" of the units. A careful study has been made to 

 determine whether the advantages of these proposed systems are such 

 as to justify the trouble and confusion incident to a general change of 

 units. No such advantage has been found. A strong reason against 

 a general change of units for the purpose of rationalization is the fact 

 that a rationalized system is obtained merely by using the ampere- 

 turn as the unit of magnetomotive force. D. J. M. 



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