222 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



numerous and good when the spots are few (fig. 8). The quan- 

 titative measurement of radio reception in the broadcast zone was 

 begun by Dr. G. W. Pickard in his priA^ate laboratory in Newton 

 Center, Mass., in February, 1926. Great credit is due to Doctor Pick- 

 ard ° for his contribution in this field and his stimulus to other 

 workers. In February, 1928, a duplicate set of apparatus was in- 

 stalled at the astronomical laboratory at Harvard University and the 

 measurements carried on there under the direction of the author. 

 Simultaneous records made for a short time at both receiving sta- 

 tions gave the necessary reduction factor for rendering those two 



Stinspot Numbers 



Radio Reception 



10 20 



February March 



1928 



FiGUEB 8. — Showing that the intensity of radio signals varies with numbers of sun 

 spots. Based on data received in Cambridge from WBBM Chicago 



series of observations comparable. The investigations at the Newton 

 Center laboratory were then shifted from the broadcast zone to the 

 region of 18 kilocycles. 



Figure 8 shows in the upper graph the inverted curve of sun-spot 

 numbers, and in the lower graph the intensity of the carrier wave of 

 WBBM broadcasting station as received in the vicinity of Boston 

 for 1926-1929, and is based upon the results of measurements made 

 by Dr. G. W. Pickard and the author, working in Newton Center 

 and in Cambridge, Mass.® The radio intensities are recorded in 

 terms of microvolts in the antenna of the receiving circuit. 



" I'roc. Inst. Radio Eng., vol. 15, nos. 2 and 9, 1927. 



• Publ. Amer. Astron. Soc, vol. 6, p. 244, 1931 ; Pop. Astron., vol. 37, p. 388, 1929. 



