STATE AGRICULTURAL SOCIETY. 255 



and tlie diurnal motion of the earth, three distinct belts or systems of 

 winds arc produced. Easterly winds in the tropical zone, westerly 

 winds in the temperate zone, and northerly or northwesterly in the 

 higher latitudes. These zones of wind move bodily to and fro with 

 the vertical rays of the sun, toward the north in Summer, and toward 

 the south in the Winter. On the movement of these zones of water 

 and air, rests the causes of the wet and dry seasons over the great area 

 of country bordering on the western coast of the United States. 



The most philosophical and scientific dissertation, perhaps, on this 

 subject, for depth of research, long and patient labor, appertaining to 

 the wind currents, climate of California and contiguous territory, was 

 made by the late lamented B. B. Redding, and read before the Acad- 

 emy of Sciences in San Francisco, in January, 1878. His observa- 

 tions are as follows: 



As California is witliin the northern temperate zone, it is primarily to the movement as a 

 body north or south of this belt of wind that we are indebted for our dry Summers and Winter 

 rains. Where, within the tropics, the northeastern and southeastern trade winds meet, is a 

 region of calms and rains. This belt of calms and rains, as has been stated, moves nortliward 

 and southward with the sun's declination. Where, within the temperate zone, the northern 

 and northwesterly winds from the polar regions meet the westerly return trade winds, is a 

 region of storms and rains. These belts also follow the sun's declination north and south. 

 Applying these laws to this coast, at our midsummer the vertical sun would be on the Tropic of 

 Cancer, and in that vicinity the northeasterly and southeasterly trade winds would meet, create 

 ascending air, consequently calms. This air, laden with moisture, would rise into cooler 

 regions, when a portion of its moisture would be precipitated, making tropical rains. This air 

 would flow north and .south, towards the poles. Confining our view to that portion which 

 would flow toward the north pole, the larger part of it must descend to the earth within thirty 

 degrees of latitude, under the law as stated by Professor Henry. As in going north it contin- 

 uously has to pass over a portion of the earth which is moving less rapidly than the portion 

 it has left, it is deflected and becomes a southwest wind. The greater portion of this upper cur- 

 rent having descended to the earth within thirty degrees, and returned to join the trade wind, 

 the remainder would flow towards the pole, portions descending in its course at all points where 

 the rarification of the air near the earth's surface would permit. These descending currents 

 cause the local variable winds of our temperate zone, but the aggregate of all of them is the 

 prevailing westerly return trade wind. The descending currents cannot give rain, as they only 

 fall to the earth when they become colder than the air near the earth's surface. In falling 

 they are constantly arriving at places of warmer temperature than those they have left; they, 

 therefore, change to a condition of taking up moisture, rather than of jiarting with it. Where 

 the great body of the descending return trade loind reaches the earth between latitudes twenty-eight 

 degrees and thirty- fire degrees, must, there/ore, on this coast, be comjiaratively a rainless region. 

 Other lessening ])ortions of the upper current would pass on until they met the prevailing 

 northerly wind from the polar regions, when their temperature would be lowered and their 

 moisture condensed and fall as rain. The conflict of this descending current with the polar 

 wind would create storms and give rise to electrical phenomena. The prevailing northerly 

 polar wind reaches to about latitude sixty degrees, varied by the declination of the sun. 



This view of the causes of the tropical, temperate, and polar zones of prevailing winds, is in 

 accordance with the theoretical deductions of Professor Ferrell concerning the course of atmos- 

 pheric currents moving on a sphere, and appears to be confirmed by the belts of low barometer 

 prevailing in the vicinities of the equator, and of latitude sixty degrees. The polar wind, being 

 colder, is heavier than the return trade wind, and where they meet, the tendenc}' is for this 

 polar wind to become a surface wind, and prevent the upper current from reaching the earth 

 until it has been reduced to the same temperature. The operation of these general laws can be 

 more clearly seen on this coast than on that of the Atlantic and Gulf States. There, the north- 

 east trade winds are forced into the great caldron of the Gulf of Mexico. The Cordilleras of 

 Central and South America and Mexico form a wall against their progress ; they rise, turn to the 

 north as an upper current, and return to the earth as southwest winds. 



Tlie Rocky Mountains, one great chain of which extends from the center of the continent north- 

 westerly to the Arctic Ocean, assist in the deflection. The great prairies extend in an unbroken 

 line in the same direction from the mouth of the Mississippi, to the same fi'ozen ocean at the 

 mouth of the McKenzie River, in about latitude sixty-two degrees. Professor J. W. Foster, in 

 his work on the "Physical Geography of the Mississippi Valley," states that the sources of the 

 Mississippi River are but 1,600 feet above the ocean. Professor Coffin has shown from the 

 records in the Smithsonian Institute, in his article on the" Winds of the Northern Hemisphere," 

 that between latitudes sixty and sixty-six degrees there prevails a belt of easterly and north- 

 easterly winds. These winds, coming from the Arctic Ocean, meet the great chain of the Rocky 

 Mountains, are deflected into northwest winds, and pass unobstructed along tliis great stretch of 

 prairie land into the States east of the Rocky Mountains. The conflict between the northwest 



