-1859] WRITINGS OF JOSEPH HENRY. 63 



the south of Lake Baikal, in Siberia. It extends some de- 

 grees lower to the south in Asia than in America. The 

 shorter diameter of the ellipse is at right angles to the longer, 

 and passes from near Behring's Straits, through the pole, to 

 the open ocean west of Norway. Its longer diameter is 

 nearly twice that of its shorter, and is in the direction of the 

 greatest amount of land in the polar regions. This form of 

 the curve and the peculiarities of the other curves are due 

 principally to the currents of the Atlantic and Pacific oceans 

 transporting the water from the equator to the north, and 

 carrying with it the higher temperature. An elliptical 

 dotted line will be perceived in the polar regions, the centre 

 of which does not coincide with the geometrical axis of the 

 earth, but is nearer the continent of North America than 

 that of Asia, thus indicating that the coldest point on the 

 earth's surface is a number of degrees south of the pole. It 

 is true, this region has never been visited by man ; yet know- 

 ing the law of the diminution of heat, and the form of the 

 other lines, the smaller one can be drawn with considerable 

 accuracy. It may be interesting to remark in this place 

 that the mean temperature of the coldest part of the north- 

 ern hemisphere has almost exactly the temperature of the 

 zero of Fahrenheit's scale; a somewhat curious although en- 

 tirely accidental co-incidence. 



We have thus far almost exclusively confined our remarks 

 to the general principles of science on which the phenomena 

 of meteorology depend; we shall now give special attention 

 to the application of these principles to the peculiarities of 

 the climate of the continent of North America, and more par- 

 ticularly to that part of it which includes the territory of the 

 United States. For this purpose it will be necessary to give 

 a brief sketch of the topography and surface of the country. 



Physical Geography of the United States. — The climate of a 

 district is materially affected by the position and physical 

 geography of the country to which it belongs. Indeed, 

 when the latitude, longitude, and height of a place above the 

 sea, are given, and its position relative to mountain ranges 

 and the ocean is known, an approximate estimate may be 



