"As the sun rises from day to day, week after week, and month after month, in unclouded brightness during the dry season, and pours down its unbroken rays on the dry, unprotected surface of the country, the heat becomes so much greater inland than it is on the ocean, that an under-current of cold air, bringing the fog with it, rushes over the coast range of hills, and through their numerous passes, towards the interior.
"Every day, as the heat, inland, attains a sufficient temperature, the cold, dry wind from the ocean commences to blow. This is usually from eleven to one o'clock: and, as the day advances, the wind increases and continues to blow till late at night. When the vacuum is filled, or the equilibrium of the atmosphere restored, the wind ceases; a perfect calm prevails until about the same hour the following day, when the same process commences and progresses as before; and these phenomena are of daily occurrence, with few exceptions, throughout the dry season.
"These cold winds and fogs render the climate at San Francisco, and all along the coast of California, except the extreme southern portion of it, probably more uncomfortable, to those not accustomed to it, in summer than in winter.
"A few miles inland, where the heat of the sun modifies and softens the wind from the ocean, the climate is moderate and delightful. The heat, in the middle of the day, is not so great as to retard labor or render exercise in the open air uncomfortable. The nights are cool and pleasant. This description of climate prevails in all the valleys along the coast range, and extends throughout the country, north and south, as far eastward as the valley of the Sacramento and San Joaquin. In this vast plain, the sea-breeze loses its influence, and the degree of heat in the middle of the day, during the summer months, is much greater than is known on the Atlantic coast in the same latitudes. It is dry, however, and probably not more oppressive. On the foot-hills of the Sierra Nevada, and especially in the deep ravines of the streams, the thermometer frequently ranges from 110° to 115° in the shade, during three or four hours of the day, say from eleven until three o'clock. In the evening, as the sun declines, the radiation of heat ceases. The cool, dry atmosphere from the mountains spreads over the whole country, and renders the nights cool and invigorating.