MEMOKANDUM ON NOTATION. 



VECTORS are denoted by letters in clarendon type, as E. 



The three components of a vector E are denoted by E x , E y , E z ; 

 and the magnitude of the vector is denoted by E, so that 



The vector product of two vectors E and H, which is denoted 

 by [E . H], is the vector whose components are (E y H z - E^H^ 

 E Z H X - E*H Z , EtHy - E y H x }. Its direction is at right angles to the 

 direction of E and H, and its magnitude is represented by twice the 

 area of the triangle formed by them. 



The scalar product of E and H is E X H X + E y E y + E^. It is 

 denoted by (E . H). 



OJ^j (1 jjj O Jjj 



The quantity -f y -I- is denoted by div E. 



The vector whose components are 



J f * t * ^ . y _ *\ 



is denoted by curl E. 



If V denote a scalar quantity, the vector whose components are 

 8F 8F 9F\ 

 - 5T * ^7' - -5T 1S denoted b 7 g rad ^ 



The symbol V is used to denote the vector operator whose 



898 



components are , , . 

 dx dy 82 



Differentiation with respect to the time is frequently indicated by 

 a dot placed over the symbol of the variable which is differentiated. 



