186 Prof. Rogers, on the Geology of North America, [Feb. 8, 



3,300,000 fresh men, pledged to exert their fullest strength through 

 20 years. Her actual annual expenditure of power, then, is re- 

 presented by 66,000,000 of able-bodied labourers. The latent 

 strength resident in the whole coal product of the kingdom may, 

 by the same process, be calculated at more than 400,000,000 of 

 strong men, or more than double the number of the adult males 

 now upon the globe. 



Climates. — Adverting to the causes of the characteristic features 

 of the North American climates, those of all the eastern and northern 

 divisions of the continent were shown to depend primarily upon the 

 peculiar distribution of the land and water, and the general circula- 

 tion of the winds and oceanic currents in the North Atlantic and 

 the Polar Basins, resulting from general phenomena of rotation of 

 the fluids, and from the configuration of those seas. The chief 

 surface currents of both these basins belong all to one great circu- 

 lating stream, which, crossing the Atlantic from Africa to the Gulf 

 of Mexico, under the northern tropic, and following for a vast dis- 

 tance the highly-heated shores of South and Central America, enters 

 the North Atlantic at Florida, under the name of the Gulf Stream, 

 carrying a temperature 5° to & higher than the mean heat of the 

 equator, and imparting to the southern coast of the United States 

 the ocean temperature of the tropics. Pursuing its career to the 

 north-east, this current transports its own mild climate to the 

 whole north-western side of Europe, and even subdues the rigours 

 of the European Polar sea ; but refrigerated, as it sweeps round in 

 its circumpolar course, the shores of Siberia and Western Arctic 

 America ; and, loaded with the annual ice of all that extended zone, 

 it streams through the great Archipelago of North-eastern Arctic 

 America, clogs its deep channels with its floating packs of ice, and 

 chills to the zero temperature of the whole hemisphere this coldest 

 of all the summer climates of the globe. Returning into the At- 

 lantic around Greenland, and by its main gassage through Baffin 

 Bay, this now arctic ice-chilled and ice-transporting current, hug-s 

 the whole north-eastern coast of the continent inside of the Gulf 

 Stream. It thus weaves a track somewhat resembling the figure 8. 

 The Gulf Stream on the south-east, and the Arctic current on the 

 north, conjointly with the tropical and the polar winds with which 

 they are connected, produce such a contrast in the temperature of 

 the southern and northern latitudes of eastern America, that all 

 the zones of the climates of the sphere are there compressed within 

 not more than 30° of a great circle, crossing the continent from the 

 Gulf Stream to lat. 70^ north of Hudson Bay. 



The climatology of the western half of the continent was next 

 discussed. There the controlling agent in the latitudes north of the 

 north-east Trade Wind of the tropic, is the south-west and west wind 

 from the Pacific Ocean, and in the Southern Atlantic States from 

 the Gulf of Mexico. This Pacific Ocean wind, moderately charged 

 with moisture in the lower latitudes, and excesssively humid in the 



