SUMMARY OF THE CONTENTS. XXI 



of the sea. The elevation of continents is still progressing slowly, and 

 is being compensated for at some definite points by a perceptible sink- 

 ing. All geognostic phenomena indicate a periodical alternation of 

 activity in the interior of our planet. Probability of new^ elevations of 

 ridges — p. 293-301 and notes. 



g. The solid surface of the earth has two envelopes, one liquid, and 

 tlie other aeriform. Contrasts and analogies which these envelopes— 

 tlie sea and the atmosphere — present in their conditions of aggrega^ 

 tion and electricity, and in their relations of currents and temperature. 

 Depths of the ocean and of the atmosphei-e, the shoals of which consti 

 tute our highlands and mountain chains. The degree of heat at the 

 surface of the sea in different latitudes and in the lower strata. Tend- 

 ency of the sea to maintain the temperature of the surface in the strata 

 nearest to the atmosphere, in consequence of the mobility of its j)arti- 

 cles and the alteration in its density. Maximum of the density of salt 

 water. Position of the zones of the hottest water, and of those having 

 the greatest saline contents. Thermic influence of the lower polar cur- 

 rent and the counter currents in the straits of the sea — p. 302-304 and 

 notes. General level of the sea, and permanent local disturbances of 

 equilibrium ; the periodic disturbances manifested as tides. Oceanic 

 currents; the equatorial or rotation current, the Atlantic warm Gulf 

 Stream, and the further impulse which it receives; the cold Peruvian 

 stream in the eastern portion of the Pacific Ocean of the southern zone. 

 Temperature of shoals. The universal diffusion of life in the ocean. 

 Influence of the small submarine sylvan region at the bottom of beds 

 of rooted algse, or on far-extending floating layers of fucus — p. 302-311 

 and notes. 



k. The gaseous envelope of our planet, the atmosphere. Chemical 

 composition of the atmosphere, its transparency, its polarization, pres 

 sure, temperature, humidity, and electric tension. Relation of oxygen 

 to nitrogen ; amount of carbonic acid; carbureted hydrogen; ammo- 

 niacal vapors. Miasmata. Regular (horaiy) changes in the pressure 

 of the atmosphere. Mean barometrical height at the level of the sea 

 in different zones of the earth. Isobarometx'ical curves. Barometrical 

 windroses. Law of rotation of the winds, and its importance with ref- 

 erence to the knowledge of many meteorological processes. Land and 

 sea winds, trade winds and monsoons — p. 311-317. Climatic distribu- 

 tion of heat in the atmosphere, as the effect of the relative position of 

 transparent and opaque masses (fluid and solid superficial area), and 

 of the hypsometrical configuration of continents. Curvature of the iso- 

 thermal lines in a horizontal and vertical direction, on the earth's sur- 

 face and in the superimposed strata of air. Convexity and concavity 

 of the isothermal lines. Mean heat of the year, seasons, months, and 

 days. Enumeration of the causes which produce disturbances in the 

 form of the isothermal lines, i. e., their deviation from the position of the 

 geographical parallels. Isochimenal and isotheral lines are the lines of 

 equal winter and summer heat. Causes which raise or lower the tem- 

 perature. Radiation of the earth's surface, according to its inclination, 

 color, density, dryness, and chemical composition. The form of the 

 cloud which announces what is passing in the upper strata of the atmos- 

 phere is the image of the strongly radiating ground projected on a hot 

 summer sky. Contrast between an insular or littoral climate, such as 

 is experienced by all deeply-articulated continents, and the climate of 

 the interior of large tracts of land. East and west coasts. Ditlerence 

 between the southern and northern hemispheres. Thennal scales of 



