DISCONTINUOUS PERIOD IN CYCLOGRAM ANALYSIS 



57 



from a base. In the cyclogram process we still keep the base available for 

 the measurement of real amplitudes by a photometric method. 



A discontinuous period, or QP, is recognized by the maximal images form- 

 ing in an obviously straight line, which means constant cycle length. The 

 features that attract attention in looking for QP's are : number of repetitions 

 of the cycle, straightness of the line of maxima, which is the same as phase 

 stability, and strong amplitude due to freedom from interfering maxima. 



A • * 



• * * * m^ • 



• • • • • 



• • • • 



a' 



d 



» n ■ ■ ■ ■ 



C^o 



f 



Fig. 27 — Comparisons between Bartels' dials a, b, c and cyclogram analysis d, e, f ; 

 a, quasi-persistence in amplitude, b, quasi-persistence in phase, and c, phase reversal; 

 d, change of period (same as continued phase change), e, phase reversal, and f, periodic 

 phase reversal. In the dial, time progresses along the bent lines; in the cyclogram, it 

 moves horizontally left to right. 



The cyclogram is built fundamentally on cycle length and so differentiates 

 at once between quasi-persistence in period and in phase. This is illustrated 

 in figure 27d, which shows a change in period at A A' by a change in direc- 

 tion of the horizontal alignment of dots. A complete 180° reversal in phase 

 is shown in figure 27e. The horizontal rows a, b, c, and d are repetitions of 

 the same sequence of maxima. A 180° phase reversal puts the new maximal 

 lines, e, f, g, and h in the same direction as before but at vertical position 

 half-way between the a, b, c, and d lines. 



