METEOROLOGY OF THE MOUNTAINS AND PLAINS OF N A, 627 



simple facts and conditions of the problem were accepted without going back to 

 their origin or cause through the meteorological processes by which these facts 

 and conditions are brought about. 



I will first call your attention to this skeleton map of North America, where 

 only the main ranges of mountains, chief lakes and principal rivers are laid down, 

 other details being omitted so as to prevent confusion. 



The principal range of mountains extending through Central America into 

 Mexico is a continuation of the Andes of South America. In Mexico, however, 

 these mountains are known as the "Sierra Madre," or ** Mother Range," and 

 which throws off two branches — one to the northwest along the Pacific Coast 

 into California, where it is known as the "Sierra Nevada" or "Snowy Range," 

 and which runs thence up into Oregon, where with a lower altitude to the range, 

 it assumes the name of the " Cascade Mountains," and where it is broken into a 

 number of detached, isolated but majestic peaks, such as Mounts Jefferson, 

 Hood, Adams, Ranier, St. Helens, etc., etc., which stand as hoary sentinels sur- 

 pliced in eternal snow to mark the gateways through which the moisture-laden 

 winds from the Pacific Ocean gain access to the heart of tne continent. 



The other and in many respects the grander branch from the Sierra Madre 

 is the Rocky Mountain Range, which runs almost due north about the iioth 

 and i2oth meridians of longitude, until reaching the parallel of 45° N. latitude, 

 where this range sinks to an elevated "divide " of from 6,000 to 8,000 feet above 

 the level of the sea. 



Lying between these ranges, and extending from the Sierra Madre to the 

 Yellowstone Park, lies a plateau or plain of comparative sterility and barren- 

 ness, comprising much of the territories of Utah, Arizona and Nevada. 



With this preliminary description of the map, I shall now proceed to discuss 

 some of the meteorological phenomena that have a direct bearing upon the ques- 

 tion before us. 



It is generally believed that the sun is the direct evaporator of humidity and 

 especially of the ocean waters, and that the evaporation from the oceans is mostly 

 from the equatorial regions of the earth, and that the vapor from this evapora- 

 tion is transported by the winds through the upper regions of the atmosphere 

 directly north and south, to its points of distribution in the temperate and frigid 

 zones. 



This, however, I think is a fallacy, and that in reality, notwithstanding the 

 enormous evaporation that does undoubtedly take place in the equatorial regions, 

 by far the greater part of that evaporation is precipitated back to the earth's 

 surface within the tropics, and that by quite a diff^erent process are the regions of 

 the earth beyond the tropics supplied with water from the heavens. 



The sun's rays being more nearly vertical within the tropics, have so much 

 the more heating power, and the surface waters of the oceans there are thus 

 brought up to a general temperature of 88° F.; from whence this heated water is 

 carried north and south to the earth's extremities, by grand ocean streams, which 

 are the life-giving arteries of the oceanic and inter-oceanic circulation. 



