338 



METEOROLOGY. 



Therefore, taking the latitudes for ordinates, and the annual in- 

 tensities in the table for abscissas, we obtain the curve of annual in- 

 tensity; and, in the same manner, the curve of annual temperature. 

 It will be seen, no doubt with interest_, that the curve of annual inten- 

 sity is almost symmetrical with that of European temperature, ob- 

 served mostly on the western side of that continent. But the curve 

 of American temperature based on the United States army observa- 

 tions for places on the eastern portion of the continent, diverges from 

 the curve of intensity, and indicates a special cause depressing these 

 temperatures below the normal standard due to their latitudes. 



At Key West, on the southern, border of Florida, the divergence 

 commences, and on proceeding northwardly continually increases in 

 magnitude; that is, so far as reliable observations have been made 

 along the expanding breadth of the North American continent. 



It were natural to suppose that the annual temperature would be 

 defined l.y the annual number of heating rays from the sun. Indeed 

 on and near the tropical regions, the curves of annual temperature 

 and solar intensity are symmetrical. But in the polar regions, the 

 irregularity of the intervals of day and night, and of the seasons, and 

 various proximate causes, introduce a discrepancy, which the principle 

 of annual average does not obviate. The laws of solar intensity, how- 

 ever, have been determined ; the laws of climatic temperature will 

 require a special and apparently more difficult analysis. 



It has been inferred ttiat there are two poles of maximum cold ahout 

 the latitude of 80° nortli, and in longitudes 95° E. and 100° W. 

 The fewness of the observations, however, in that remote hyperborean 

 region, leaves this question still open to investigation. 



SECTION VI. 



AVEIIAGE ANNUAL INTENSITY OF THE SUN UPON A PART OR THE WHOLE OF 



THE EARTH'S SURFACE. 



Having determined the sun's vertical intensity upon a single unit or 

 point of the earth's surface, let us next ascertain the average annual 

 intensity upon a larger area, a zone, or the entire surface of the globe. 

 After which, we shall glance at some of the climatic alternations which 

 are most clearly made known and interpreted by the mechanism of 

 the heavens. 



In any zone of the earth the sum of the annual intensities divided 

 by the suri'ace will evidently give the mean annual intensity upon 

 the unit of surface. On this principle the following results were 

 derived, but the analytic process is here omitted: 



