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that they hope in vain for rain, and also hope in defiance of the laws 

 that control climate. 



A LAW OF CLIMATE. 



They live in a section of the State that is an exemplification of the 

 truth of the law well stated by Guyot: "That when a mountain 

 chain opposes a horizontal wind, the air is forced up along the slopes; 

 its vapors are condensed, and water the side exposed to the wind, 

 while, on the opposite slope, the same wind descends into the valley 

 dry and cloudless." 



The western slope of the Mount Diablo Range, in the latitude of 

 San Francisco, receives about an annual average of twenty inches of 

 rainfall. Ellis — in the same latitude on the eastern side of the same 

 range — lias but an annual average of nine and twenty-two one-hun- 

 dredths inches. Modesto, a few miles further south, on the opposite 

 side of the San Joaquin, has but eight and ninety-five one-hundredths 

 inches. Still further south these averages continue to decrease, until, 

 on the west side of Tulare Lake, the annual rainfall cannot exceed 

 three inches. The record at this point has been kept for so short a 

 period that the amount cannot be stated positively; but applying to 

 this section of the State the well known laws controlling climate, it 

 will be found in time that this estimate is not far from correct. I 

 have thought it of interest to condense some of the results of all these 

 observations, as they show that, considering the elements of disturb- 

 ance in the facts that this State has on one side the vast Pacific Ocean, 

 presenting a uniformly radiating and absorbing surface, and on two 

 other sides vast tracts in the Colorado, Mohave, and Nevada Deserts, 

 presenting rapidly radiating and absorbing surfaces, yet California is 

 controlled by the same universal laws that control climate in other 

 places. A statement of some of these laws, and the application of them 

 to the records obtained of the temperature, prevailing wind, and 

 annual rainfall, and it will be seen that until the Isthmus of Panama 

 sinks beneath the ocean and allows the Gulf Stream to pursue its 

 way into the Pacific, or some other great change takes place in the 

 physical geography of the earth, the climate of any given section of 

 this State is not exceptional, but just such as these laws show it 

 should be. Professor Joseph Henry, in his " Contributions to Meteor- 

 ology," has done so much to clear up the mystery of the winds, and 

 has stated these laws so concisely, that it is a pleasure to quote from 

 him. He says: 



If the earth were at rest, it is obvious that the air expanded by the sun's heat at the equator 

 would rise up and flow over, descending, as it were, an inclined plane towards the poles, when' 

 it would reach the earth's surface and flow back to the equator, and thus a perpetual circulation 

 would be maintained. It is farther evident that, since the meridians of the earth converge, all 

 tli'' air that rose at the equator would flow along the upper surface entirely to the poles, but the 

 greater portion would proceed no farther north or south than latitude thirty degrees, for the siii-- 

 Pace of lli" earth contained between the parallel of this degree and the equator is equal to that 

 of half of the whole hemisphere. Portions, however, on the northern hemisphere would flow 

 on, to descend at different points further north; and of these portions some probably would 

 reach the pole, and there sink to the surface of the earth, and from that point diverge in all 

 directions in the form of a northerly wind. 



Between the two ascending currents near the equator there would be a region of calms or vari- 

 able winds. The currents which flow over towards the poles would descend with the greatest 

 velocity at the coldest point, because there the air would be densest. Now. the earth is in rapid 

 motion on its axis from west to east, and every particle of air. therefore, Slowing from the north 

 to the equator would partake of the motion of the place at which it started, and would reach in 

 succession lines of latitude moving more rapidly than itself. It would therefore' lag behind 

 continually, and appear to describe on the surface of the earth a slightly curvilinear course 



