HIGHER HARMONICS. 



77 



Fig. 23 shows a curve C compounded of the fundamental and 

 the first harmonic ; in Fig. 24 the curve C is compounded of the 

 fundamental and the second harmonic ; in Fig. 25 the curve C is 

 compounded of the fundamental and the third harmonic ; in Fig. 26 

 the curve C is compounded of the fundamental and the first and 

 second harmonics ; in Fig. 27 the first and third harmonics are 

 present ; in Fig. 28 the second and third harmonics are present ; 

 whilst in Fig. 29 the curve C is compounded of the fundamental 

 and the first, second, and third harmonics. In each case A is the 

 fundamental curve, & 2 , &s> #4, the first, second, and third harmonics 

 respectively, and C the resultant curve. 



FIG. 29. 



The first, third, etc., harmonics are called the even harmonics, 

 because their periodic times are even submultiples of that of the 

 fundamental. The second, fourth, etc., harmonics are, for like 

 reason, called the odd harmonics. 



The reader should practise drawing curves compounded of the 

 fundamental and harmonics, as they are very instructive. 



51. It is a matter of experience that the even harmonics are 

 generally absent from the curves representing alternating currents 

 and E.M.F.S, so that we may legitimately represent them by 

 expressions of the form 



sin (pt - Oi) + a 3 sin (Spt - 3 ) -f a 5 sin (5pt - 6 ) + 



etc. 



