234 ABBOT: SOLAR RADIATION MEASUREMENTS 



variations and changes of terrestrial temperatures at Buenos 

 Aires occur in opposite senses at different seasons of the year. 

 From October to February, inclusive, low values of solar radia- 

 tion are followed for several days by negative temperature de- 

 partures from the normal, and the reverse is true for the months 

 March to September, inclusive. Naturally the intervals of tran- 

 sition in March and October from one of these conditions to the 

 other are periods when the solar radiation results are at present 

 of little value for forecasting purposes. Besides this inconven- 

 ience, it occasionally happens in the midst of one of the long 

 periods of positive or of negative correlation, that a sporadic 

 regression to the other type of correlation will occur to mar the 

 forecast. It may be that with further investigation these things 

 will be understood. Something about the prevailing direction 

 of the winds or of the condition of the upper air may come to 

 light to serve as a basis of prediction whether the correlation 

 will be positive or negative at a given epoch. 



It has been mentioned that Mr. Clayton discovered in his 

 early studies that in different parts of the world correlations of 

 opposite algebraic signs between solar radiation and temperatures 

 prevail simultaneously. It must, therefore, be tha tthere are geo- 

 graphical regions of transition, as well as transition time epochs at 

 a single region. Hence the new means of forecasting cannot yet be 

 regarded as either simple or fully satisfactory. Much investiga- 

 tion must be made before they take established rank in meteor- 

 ology. Enough has been done to show that there is promise. Before 

 the promise can come to fruition we must have continuous daily 

 records of well determined solar constant values. These can- 

 not be secured with the means now available. The solar radia- 

 tion station at Mount Wilson is not occupied more than six months 

 per year, and never yields more than 130 values of the "solar 

 constant" in that period. Of those not all are good. The sta- 

 tion at Calama yields about 250 good values per annum now 

 that the new method of observing is adopted. These are the 

 only stations of the kind in the world. There should be two 

 or three others, widely separated in the most cloudless regions 

 available. I have in mind Egypt, Southern California and Mid- 

 dle Australia. 



