12 NUMBER. [INT. I. 



The vector product of two vectors is drawn with respect to 



their plane in such a manner that 

 the rotation of a right-handed screw 

 advancing in the direction of the 

 vector product would turn the first 

 vector towards the second, as is seen 

 R| by making the two vectors coincide 



2 * with two of the unit vectors i, j, k. 



If two vectors are parallel, their vector product is zero. The 

 vector and scalar products of two vectors cannot vanish simul- 

 taneously unless the tensor of one of the vectors vanishes. 



NOTE. Although the above consideration of vectors has been 

 inserted for the sake of logical connection, we shall seldom make 

 use of the conception of a vector as a complex number, and when 

 the term complex number is made use of we shall mean a complex 

 number in the narrow sense. We shall frequently use the terms 

 vector, scalar product and vector product, the latter being defined 

 by the equations (i) and (2) above. 



