INSTEUMENTS AND TECHNIQUE 47 



because longitudinal displacement has been turned to transverse, 

 thus making a departure from a straight line which is at once apparent. 



Invention and name — This pattern was first designed by the writer 

 in 1913 and published in 1914 under the name of a multiple plot.* 

 Its automatic production by this method of interference was worked 

 out that same year and published in 1915. It was then called a 

 differential pattern and was used as the basis from which to photo- 

 graph a true periodogram, as described in Volume I. In the present 

 volume, however, the periodogram is omitted, since there has been 

 very little use for it in comparison with the pattern. With the con- 

 struction of small portable instruments for producing this pattern, 

 the word cycloscope has come into use as their name. In a correspond- 

 ing way the large analyzing instrument with its photographic attach- 

 ment, constructed with the fund given by Mr. Clarence G. White, of 

 Redlands, California, has come to be called the White cyclograph; 

 the photographs obtained by it are here called cyclograms. 



THE WHITE CYCLOGRAPH 



During the building of the previous instrument in 1918 the thought 

 in mind was the production of a periodogram as suggested by Schuster. 

 But with the extensive use of that instrument it became apparent 

 that the differential pattern or cyclogram designed as merely one 

 stage in the process was far more important than the periodogram. 

 The periodogram merely produces the kind of results that come from 

 a mathematical process; the cyclogram contains far more than that. 



At the same time, the long track of the periodograph compelled 

 the observer to walk indefinitely back and forth in an awkward 

 position. So it was first intended to arrange a mechanism to eliminate 

 this walking, but as it took form the lessening importance of the 

 periodogram was realized and the attachment for producing it was 

 omitted. It could, however, be added at any time if thought worth while. 



Illuminator — The arrangement for mounting the cycle plot so 

 that fight comes through in the proper way is called the illuminator. 

 For a long time daylight was used, thrown onto the curve in a dark- 

 ened room by a slant mirror at the base of a window. Then thin 

 white tracing-paper replaced the mirror and gave a broad area for 

 comparing different curves. One curve some 40 inches long and 4 

 wide was insufficient and a second could be put above it. But for close 

 comparison of many curves for dating purposes a light frame sliding 

 vertically was arranged to carry 10 curves at once. This frame was 

 suspended by a cord over a pulley and analysis could pass from one 

 curve to another at any desired speed. 



*It appears to be identical with Clayton's "phasogram" in World Weather, page 379. The 

 multiple-plot method of making a periodogram was described to him in conversation in the 

 summer of 1913, and he remarked, "Well, you might expect an astronomer to work out an optical 

 method." 



