SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 80 



the variations of the smi's total radiation and the variation of the vis- 

 ible spottedness. 



A second trial of the new method of testing solar variation was 

 undertaken with the observations of the Smithsonian station at Mt. 

 Montezuma, in Chile, from 1920 to 1926. The work was carried 

 through for each of the twelve months of the year. In this method 

 of working, one determines the general mean values, including all 

 the selected days for all the months of a given name, as, for instance, 

 the month of January, both for the selected pyrheliometry and for 

 the published solar constant values. He then determines the per- 

 centage differences of the mean values of each individual month of 



Fig. 



TT 



19 



15 lb 17 le 



-Selected pryheliometry, solar constant, and sun-spot nu 

 compared. Mt. \\'ilson work, Julys 1910-1920 



nibers 



January for the series, from the appropriate general mean. If no 

 changes of scale in the solar constant observations occur, the two 

 series (pyrheliometric and solar constant) ought to show, within 

 experimental error, the same march of the percentage deviations ; 

 but if, owing to the introduction of new observers, new methods of 

 observation, or of reduction, the scale of the solar constant values 

 is altered from time to time, then the correspondence between the 

 two series is impaired. Such, indeed, proved to be the case at Monte- 

 zuma. The accompanying table gives the collected results on selected 

 pyrheliometry and solar constants for all months from 1920 to 1926. 

 I give the weights and the weighted mean percentage departures 

 in each instance. It will readily be seen by comparing the differences 

 of percentage departures, as given in italic type, that for consider- 

 able intervals these differences run along roughly alike from month 

 to month and then abruptly change. In this way they indicate 

 that several small changes of scale occurred in the solar constant 

 observations. 



