INTRODUCTORY NOTE 



By C. G. abbot, 

 assistant secretary, smithsonian institution 



In publishing Mr. Hoxmark's paper, the Smithsonian Institution 

 is glad to bring to the notice of English-speaking people the results 

 which have come from the acceptance of the evidence of solar vari- 

 ability as a working hypothesis by the Weather Service of Argentina. 

 The preliminary investigations in this line by Mr. H. H. Clayton, 

 when he was official forecaster of Argentina, were publis^hed by the 

 Institution in Volume 68, No. 3, of the Smithsonian Miscellaneous 

 Collections, and these studies led to the attempt to forecast tempera- 

 tures and precipitation at Buenos Aires based on solar-radiation 

 measurements made by the Smithsonian observers at Calama and 

 Alontezuma, Chile. 



These forecasts, begun in December, 191 8, by Mr. Clayton, and 

 continued since June, 1922, by his successor, Mr. Hoxmark, have 

 given rise to the present paper by the latter. The temperature fore- 

 casts are given not in general terms such as most forecasters content 

 themselves with using, but state precisely for a narrow locality the 

 exact temperatures to be expected, morning and evening, to the end 

 of the eighth day after the forecast is published. Verification consists 

 in taking differences between observed and forecasted temperatures 

 and the normal depending on many years records, and computing 

 correlation coefficients therefrom, according to the well known 

 methods of Galton and Pearson. 



This, it goes without saying, is a very severe test. An error of 

 12 hours in the time when a sharp riee or fall of temperature is 

 predicted, even though the reality and magnitude of the change is 

 truly forecasted, will often give large departures which ruin for 

 the time the correlation between forecast and event. Moreover, the 

 results of Clayton, which appear in the next preceding serially num- 

 bered paper of these Miscellaneous Collections, show that even a 

 half per cent change in solar radiation produces notable temperature 

 changes. The accuracy of Smithsonian solar-radiation observations 

 is not adequate to prevent many errors as great as half of one per cent, 

 or even twice that magnitude occasionally. Hence, on this account, 

 also, the solar forecaster is at a disadvantage. 



