Chase.] 



314 



[February. 



The averages at individual stations often present considerable 

 variations, even when different decades, or longer periods, are com- 

 pared. It is, therefore, uncertain to what extent the laws of limited 

 local change are manifested by this table, but in the extended group- 

 ings of countries, divisions, continents, and hemispheres, I think the 

 indications of the ratios can be safely trusted. 



By taking the differences from month to month (instead of the 

 aggregate increase from the winter solstice), we may form some idea 

 of the change at different periods of the year, in the relative climatic 

 influence of the sun and the winds. The method of comparisoa 

 may be readily understood by referring to the following table. The 

 small figures denote the ratio ( ^ of sines, or ^ of arcs) to which the 

 increment most nearly approximates. The sums of the monthly 

 diflPerences give the aggregate ratios of the preceding table. The 

 first series of means is derived directly from the tabular numbers, by 

 allowing equal weight to each; the second allows to each ratio a 

 weight corresponding to the territorial area. 



Monthly Eatios of Change in Sine, Arc, and 

 Temperature. 



These comparisons seem to warrant the following inferences, all of 

 which are confirmed by a more extended and minute examination, as 

 well as by other considerations. 



1. Taking into view the entire land surface of the globe and the 

 entire range of the year, the direct heat of the sun, and the induced 

 aerial currents appear to be about equally instrumental in determin- 

 ing fluctuations of temperature. 



* The sines employed in each table are merely the sines of the excess of me- 

 ridian altitude above the minimum, and not the increment of the sine of least 

 meridian altitude. If the hitter had been used the number of ratios approxi- 

 mating most nearly to the differences of arc would have been much greater. 



