286 F. H. Bigelow — Studies on the General Circulation 



To illustrate a few of these points, take the stations in the 

 United States, Washington, Key West, Galveston, St. Louis, 

 Salt Lake City, Phoenix, San Diego, and sum the departures 

 as follows in four groups, in Table 2 : 



Eastern Districts, Wash., K. W., Gal., S. L. and take mean r 3 



Western Districts, Salt Lake, Ph., S. D. « « " Tt> 



Inland or Northern, Wash., S. L., S. L. C, Ph. " " •< r 3 



Coast or Southern, K. W., Gal., S. D. " « " r 4 



If now we combine t, and t 2 in a general sum, taking the sum 

 of the positive values of t i3 and setting against r 2 the algebraic 

 sum as it comes, in order to see whether there is inversion or 

 not within the United States, we find the following results : 



When T i = + iO'?, r 2 = — 4-2 



r 1= - 10-1, r 2 = + 1-9 



showing that there is a tendency to inversion between eastern 

 and western districts. Similarly, 



when t 9 = + 11-0, r 4 = 0*0 



t. s = — 10-4, t 4 = — 0-9 



showing that when the inland or northern districts vary the 

 tendency is for the coast and southern districts to fluctuate 

 accidentally. The smallest variations in the United States are 

 on the Southern Pocky' Mountain plateau, and the largest in 

 the Lake Pegion. Similar studies should be made of residuals 

 before attempting to combine them, because the same external 

 and general cause produces inverted effects through the action 

 of the complex circulation of the atmosphere, as will be 

 explained in other papers. 



The size of the annual departures demands a statement as 

 regards their value in practical meteorology. On the face of 

 it, the annual variations on the normals are small, and they show 

 that there is no secular progressive change in the conditions of 

 the climate. An examination of the daily and monthly means 

 from which the annual means are divided shows that the years 

 divide into two classes, (1) those of wide oscillations and those 

 of narrow oscillations. When the years of wide swing occur 

 it implies that the cold polar currents and the warm tropical 

 currents which meet in the United States are each respectively 

 more pronounced, colder and warmer in succession, than in 

 the quiet years. This intensification of warm and cold cur- 

 rents is due to an increase in external solar radiation, which 

 produces a stronger general and a more irregular local circu- 

 lation. Now the mean of these wide oscillations of the several 

 months in a year, amounting in the winter in the Lake Region 

 to as much as plus 18° F. to minus 18° F., will be about the 



