Bigelow — Meteorological Elements of the United States. 411 



Aet. XLY. — The Relations between the Meteorological Ele- 

 ments of the United States and the Solar Radiation /* 

 by Frank H. Bigelow. 



In attempting to trace out any synchronous relations which 

 may exist between variable sources of energy in the sun and 

 their corresponding effects in the atmosphere of the earth, there 

 are three considerations which must be carefully complied 

 with, or else the existing relations will be entirely smothered. 

 (1) The complete homogeneous series of all data must be pro- 

 vided, eliminating local conditions at the station and employing 

 a uniform system of reductions. (2) The summation of the 

 residuals must not be made strictly periodic at the earth unless 

 the solar action is also strictly periodic. As this is not the 

 case at the sun, the synchronism at the earth must be traced 

 through only roughly periodic variations. The 33-year period, 

 the 11-year period and the 3-year period are known to have 

 wide variations in length and amplitude, but the solar intervals 

 should be compared with the terrestrial intervals as they occur, 

 without forcing a uniform period upon them. (3) The temper- 

 atures of the United States are more the product of heat which is 

 transported in the general circulation than of direct solar 

 radiation, so that the main features of the circulation must be 

 admitted to be the connecting link between the periods. Thus, 

 an increase in solar radiation will increase the heat energy and 

 temperatures of the tropics, but this will be followed by a 

 decrease in the temperatures of the middle latitudes, because the 

 return currents from the polar zones transport an excess of cold 

 air towards the tropics, over the temperate zones, which is to 

 compensate for the increase of warm air transported in the 

 upper levels towards the polar zones. All the complex circu- 

 lation observed in the earthy atmosphere stands between the 

 solar radiation and the temperature effects in any latitude. 

 Especially does this become an important feature in the United 

 States, where the influences of the circulation are vigorously 

 registered in the prevailing powerful cyclonic action. The 

 question whether there are variations in the observed solar 

 phenomena, numbers of the prominences, faculae and sun-spots, 

 which are synchronous with the observed magnetic and meteor- 

 ological elements on the earth, is one simply of statistical 

 comparison and analysis. The other question of the cause of 

 such synchronism, if it exists, the mode of transferring the 

 variable energy of the sun's output to the earth, may properly 



* Eead before the Philosophical Society of Washington, Feb. 1, 1908. 



Am. Jour. Sci.— Fourth Series, Vol. XXV, No. 149.— May, 1908. 



28 



