2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



constant " of radiation ending with the year 1930. Similar measure- 

 ments, as yet mostly unpublished, have been continued till the present 

 time. Some of them have been broadcasted daily through Science 

 Service, but they are not yet to be regarded as definitive until their 

 further comparison and adjustments with results of other observing 

 stations is completed. Nevertheless, they will serve for our present 

 purpose. 



This study relates to the daily departures from normal temperatures 

 at Washington, D. C, St. Louis, Missouri, and Helena, Montana. 

 These departures have been computed as follows : The general means 

 of monthly averages of maximum and minimum thermometer for 

 many years are used as printed on pages 956, 922, and 861 of World 

 Weather Records (Smithsonian publication no. 2913). These monthly 

 values, treated as representing the middle days of the months, were 

 plotted on an adequate scale. Daily values were read from the smooth 

 curves. The departures from these daily normals were then obtained 

 for all days from January i, 1924, to January 31, 1935, by subtrac- 

 tion from the current United States Weather Bureau Reports. 



In order to fix the dates when sequences of rising and of falling 

 solar emission of radiation occurred, Montezuma solar-constant values 

 were used. As it was intended to segregate the investigations of each 

 of the 12 months of the year separately, 12 solar-constant plots were 

 made, each of which contained all of the values observed within a 

 given month in all the years 1924 to 1935. Values of small weight 

 were given the symbol " U " to identify them, and apparent sequences 

 depending largely on such days were rejected. 



That the reader may see how incomplete the record is, even from 

 so fine a station as Montezuma, I give in figure i the plots for Janu- 

 ary and for April. It is beheved that the reader will appreciate how 

 hard it is to decide which are the satisfactory cases of rising and of 

 falling sequences of solar change. After much scrutiny of the plots, 

 the following dates were selected as zero dates of solar changes. 



Before presenting the associated temperature departures for Wash- 

 ington, St. Louis, and Helena, attention is drawn to four criteria 

 which should hold if solar variation really affects terrestrial 

 temperatures. 



I. Since opposite causes generally produce opposite effects, what- 

 ever curves may represent the average courses of the temperature 

 departures following rising solar sequences, they should be opposite, 

 as the right hand is to the left, to the average curves representing the 

 after effects of falling solar sequences. 



