226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



Generally speaking, reception should be better in the winter months 

 on account of the shortened days and decreased daylight. On the 

 other hand, the sun spots and radio curves of 1926-1928 show that 

 the increased solar activity gave much poorer reception in the winter 

 months of both 1926 and 1927 than during the summer months of the 

 same years. Conditions again improved in 1928, but reception again 

 became poor in the fall and winter of 1929. It may be mentioned 

 that the high degree of static due to thunderstorms in the summer 

 months results in the fact that the average radio listener will decrease 

 the sensitivity of his set in summer to lessen these disturbances with 

 the necessary accompaniment of low audible intensity of distant sta- 

 tions. Hence the general impression of a low intensity accompanying 

 warm weather temperature. 



The radio reception registered in 1929 has tended to follow the 

 same 15-month cycle in the sun-spot numbers with a marked depre- 

 ciation during the recent fall maximum, when, under normal condi- 

 tions, radio reception should have been improving with the decreasing 

 hours of sunshine. 



Some progress has been made by Doctor Pickard and others in the 

 correlation of the temperature changes with radio reception, and 

 while concomitant variation markedly exists it is doubtful if the 

 relation is one of cause and effect. It seems far more plausible that 

 changes in the solar activity are more directly responsible for varia- 

 tions in the signal strengths received than that such should be de- 

 pendent upon any absolute values of atmospheric temperature. 



The subsequent rise in sun-spot numbers corroborated to a remark- 

 able degree a prediction ventured at the New York meeting of the 

 American Association for the Advancement of Science, in 1928, that 

 the period of maximum for the present 11-year cycle had not been 

 passed. Forcasting on the basis of the 15-month cycle, which had 

 worked so effectively during the preceding years, the year 1930 was 

 expected to show a general decrease in sun-spot numbers as the 

 year waxed, with a corresponding increase in radio signal strength in 

 the broadcast zone. By the very end of 1930 and the beginning of 

 1931 the general rise of a secondary sun-spot maximum became 

 evident. By 1931, however, it was believed that we should be so 

 far from the maximum of the 11-year period that the secondary 

 maximum period should have no such marked effect upon radio 

 reception and allied electromagnetic phenomena as did the sun-spot 

 maxima of 1928-29. Such has been proven to be the case by the sub- 

 sequent observations. The curve of radio intensities received since 

 observations have been made at the Perkins Observatory is shown in 

 Figure 12, the ordinates increasing from the top toward the bottom 

 of the figure. The trend of this inverted curve of radio reception 

 with the curve of decreasing sun-spot numbers is self-evident. The 



