256 TRANSACTIONS OP THE 



polar winds and the moisture laden southwest winds from the Gulf of Mexico, gives all the 

 Atlantic States north of Florida their Summer rains. As far back as 1850, Professor Espy, in his 

 second report on meteorology to the Secretary of the Navy, without, at that time, more than 

 suspecting the cause, reported as the result of a long series of observations, that in the northern 

 part of the Atlantic States the winds generally, in great storms, set in from north of east, and 

 terminate from north of west, and in the southern part of the Atlantic States they set in from 

 south of east and terminate from south of west. 



It is doubtful if the Atlantic trade winds ever give rain to California. That portion which 

 passes the mountains through the valley of the Rio Grande, precipitating its moisture on the 

 White Mountains and Black Hills of Arizona, which, by the meteorological records of the 

 Smithsonian Institute, are shown to have an annual average of twenty inches of rain. 



That these general laws may be applied to California as the cause of our climate, I will 

 assume to follow a given portion of air along well known jjoiuts on the coast. At midsummer, 

 at noon, the sun would be vertical in Southern California just north of Cape St. Lucas. In this 

 vicinity, this portion of air, having been a part of the trade wind, would have become heated 

 and saturated with moisture. It would rise until it met colder regions, when it would part 

 with some of its moisture; a portion would return to the earth within thirty degrees, again to 

 join the trade winds, and another portion pass on towards the north as a part of the great upper 

 current. Under the operation of Professor Henry's law, the greater part must return to the 

 earth between latitude thirty degrees and, say, latitude thirty-five degrees ; the remainder would 

 flow on towards the pole until it met the prevailing northwesterly winds; at these points there 

 would be fogs and Summer rains. Whenever the polar wind forced its way south of this, it 

 would condense the moisture of these descending return trade winds and give rain. This they 

 would do until they had passed so far south that their temperature would be raised to that of 

 the descending return trades, when, of course, no moisture could be precipitated. It is these 

 jjolar winds, forcing themselves among the descending return trade winds, that give British 

 Columbia, Washington Territory, and Northern Oregon their Summer showers. Should they 

 force themselves further south, they, in their passage, have to pass into warmer latitudes; they 

 would also meet the heat of our great valleys and deserts, and become as warm as our prevail- 

 ing Summer wind, and, therefore, could not give California Summer rains. 



But, from midsummer, the sun is for six months moving south, taking with him the great 

 belts of winds of the trojDical, temperate, and polar zones, until, at our midwinter, his rays are 

 vertical just north of the northern part of Chile, in South America. These belts, moving south 

 with the sun during six months, the region of conflict between the polar winds and the variable 

 winds which in Summer was over British Columbia, Washington Territory, and Oregon, has 

 now moved south over Oregon and the northern and 'middle part of California. The temper- 

 ature of the earth's surface and the air in contact with it, have been lowered by the withdrawal 

 of the sun's more direct rays, and the f)olar winds are permitted to reach further to the south 

 without increasing their temperature. The region of calms and the southern limit of the 

 variable winds have, of course, also moved south with the sun, beyond the Tropic of Cancer. 

 At this season, in the Pacific, the trade wind is not usually found north of latitude thirteen 

 degrees, when, in Winter, the descending return trade wind, coming from the southwest, meets 

 the coast south of Cape St. Lucas, it is forced by the Cordilleras and the configuration of the 

 main coast into the Gulf of California, and is deflected into a course from the southeast, or, to 

 be more exact, as shown by the records kept by Dr. Gibbons, into a course from the south-south- 

 east. Without doubt, the southwest return trade wind which strikes the coast of Lower Cali- 

 fornia in Winter north of Cape St. Lucas, is deflected by the high mountains parallel to the 

 shore, and also passes over our coast counties as a soutlieast wind. H. S. Warner, in a paper read 

 before the American Association for the Advancement of Science at its Baltimore meeting in 

 1858, was the first to note the fact that the waters of the Gulf of California sujDply the moist- 

 ure to the southeast wind that bears to us our rains. It may be objected that the Gulf of Cali- 

 fornia has not sufficient area from whence could be delivered the great volume of southeast 

 winds that, at times, during our Winters, flow over this State. The gulf is not the cause of 

 this wind, but it is the channel through which it flows, and gives to it direction. When the 

 sun is vertical on the coast of Bolivia, just north of Chile — -at our midwinter — he has carried 

 south with him the northeast trade winds, until, as has been stated, they do not prevail north 

 of about latitude thirteen degrees. The region of calms, where the great body of the upper 

 current returns to the earth again to join the trade winds, is, at this season, between latitudes 

 thirteen and eighteen degrees. North of this region of calms, at this time, those portions of 

 the upper current which pass further north, descend to the earth, under Professor Henry's law, 

 as southwest winds. At latitude twenty degrees, the west coast of Mexico projects a bold head- 

 land into the Pacific Ocean, known as Cape Corrientes. South of the Cape the trend of the 

 coast for nearly two thousand miles is east-southeast; north of this cape, the trend of the coast 

 for more than one hundred miles, to Mazatlan, is north; from Mazatlan to the head of the Gulf 

 of California, a further distance of six hundred miles, it is north-northwest. The Sonora arm 

 of the Cordilleras rises above the table land of Mexico, at latitude twenty degrees, and runs 

 north-northwest along the coast, nearly to the head of the Gulf of California. All of these 

 southwest winds that strike the coast from Cape Corrientes north to Cape St. Lucas, are deflected 

 by these mountains and forced up the Gulf as south-southeast winds. The United States Coast 

 Survey have lately completed the survey of this gulf and parts of the Mexican coast north of 

 Cape Corrientes. When their record of observations of the course of the prevailing winds in 

 Winter, the barometric pressure and the temperature of the air and water is published, I feel 



