6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



2. There is a strong frequency in column 4, showing that another 



■ r 6.648s , 



regular periodic solar variation exists of - — ^^ =3.3242 days in 



period. Its phases coincide with those of the primary period when- 

 ever possible. 



3. There is no appreciable difference in lag between Washington and 

 New York in response to the solar variations. In short, the two sta- 

 tions behave nearly alike in all respects. 



SO 



30 



20 



10 



7 / 



Fig. I. 



MAGNITUDE OF THE EFFECT 



Owing to terrestrial interferences in lag and otherwise, and to the 

 interference caused by the existence of the scondary solar period of 

 half the length of the primary one, the positions of maxima and 

 minima fluctuate. Comparatively seldom does a whole month go by 

 without shifts of i, 2, or rarely 3 days in the place of minima. On 

 this account the mean monthly values seldom show the full measure 

 of the effect of the solar change on terrestrial temperatures. How- 

 ever three months have been selected from many among the tempera- 



