APPENDIX 



STUDIES OF THE CYCLOGRAPH 

 By Edmund Schulman 

 INTRODUCTION 



The cyclograph is an optical-mechanical instrument to aid in the detec- 

 tion of cycles in variable phenomena. When plotted in a curve, data of this 

 type are transformed by the cyclograph into a pattern whose interpretation 

 by the observer represents a cycle analysis. This pattern is highly sensitive 

 to changes in position of moving parts of the instrument and thus enables 

 analysis over a continuous and large range of cycle lengths. The readable 

 display in the pattern of complex and frequently hidden changes in the char- 

 acter of cycles in natural phenomena makes cyclograph analysis not only a 

 rapid but a highly powerful method, in solving many cycle problems such as 

 those encountered in climatic studies. 



However, since the cycle results are obtained by interpretation of a pat- 

 tern, it is relevant to inquire how much the personal element influences the 

 results. The comparison of the analyses of two or more independent observ- 

 ers is thus indicated. The following discussion is principally concerned with 

 such an investigation; some studies which are in part supplementary to simi- 

 lar material in Chapter II of this volume are also included. 



DESCRIPTION OF THE INSTRUMENT 



The cyclograph as used at present in the Tree-Ring Laboratory is sub- 

 stantially the same as described by Dr. Douglass in 1915, 1919 and especially 

 1928 (see Bibliography), although some minor modifications were introduced 

 in 1931-32. In skeleton outlines, the instrument has three major parts. 



(1) The Light Source — This consists of a horizontal series of light bulbs, 

 in back of which is a mirror, and in front of which is a diffusing screen. This 

 screen forms a window, measuring 44 inches horizontally by 3 inches verti- 

 cally, in which may be placed for analysis a cycleplot 1 of any curve. All 

 the holes in the cycleplot therefore receive a uniform illumination. 



(2) Movable Mirror Carriage — The mirror carriage is suspended from a 

 two-rail track which is 7 feet above the floor and runs about 40 feet horizon- 

 tally, beginning some 6£ feet from the window. The carriage holds two 

 mirrors, 5.5 inches by 25 inches, each inclined 45 degrees to the vertical with 

 the reflecting surfaces toward each other and facing the window. Since the 



1 A curve plotted on opaque paper, and maxima cut out. See pp. 44 and 149. 



143 



