APPENDIX 147 



to the cross-hair as axis. Then it is easy to show that the angle of inclination 

 6 of the alignment is given by 



H) 



(1) tan0 = (1 — £J tani 



where i is the inclination of the analyzing lines. 



p is the period length of the mirror setting. 



c is the cycle length represented by the alignment. 

 From (1) we have 



(2) c= ptani 



tan i — tan 



If the sweep lines are inclined at an angle <j> to the horizontal cross-hair 1 

 we have the more general case 



(3) tan t - (C - P) sin * sin ! 



p sin (0 — i) + (c — p) sin <j> cos i 

 and 



(4) c - p (l + tanflsin(0-i) \ 



\ (1 — cot i tan 0) sin <f> sin i/ 



With <j> = 85° and i = 102° as in cyclograms in this volume (4) becomes 



/r . 1—0.09 tan 



(5) c = p 



v ' v 1-O.21tan0 



CONSTRUCTION OF FREQUENCY PERIODOGRAM 



To produce a periodogram summarizing the analyses of a number of curves, 

 the procedure is first to make up a cycle diagram (see fig. 57). Each cycle in 

 every analysis of the series is entered in the diagram with its weight, the 

 numerical value of which is that given in the following table. To expedite 

 the formation of the diagram, the cycle weights are sometimes represented by 

 symbols as follows : 



A plot is made on the standard 2-mm. graph paper used in the Labora- 

 tory; cycle lengths, one scale unit per centimeter, are plotted as abscissae, the 



1 An apparent inclination of the sweep lines to the vertical will arise when the cross- 

 hair is not precisely horizontal. 



