Carnegie Inst. Washington Pub. 289. Vol. Ill — Douglass 



Years 

 -8 



PLATE 12 



84 



11.3 



16.9 



9.8 



A B 



Periodograms 



A. Periodogram (1913) of sunspot numbers since 1760. 



B. Periodogram (1918) of variable star, R Arietis, showing period of 187 days (see 

 Appendix). 



