248 NINTH ANNUAL REPORT OP 



carpeting shows on the hills at the distance of five miles. With the 

 drought of June comes the winter of vegetation. 



I have something more to say in regard to the course of the winds 

 and clouds during rain, and on the subject of mists and dews. 



No. 5.— RAIN, STORMS, CLOUDS, AND MISTS. 



In my last article I inquired whe;her moderate rains, such as have 

 fallen at San Francisco, would be adequate to the production of the 

 floods of last March; and I stated that a single inch ot"rain, poured into 

 the river from a surface of 1,000 square miles, and forming a current of 

 four miles an hour, would raise the river at Sacramento to eight feet, 

 and keep it at that height 24 hours. When we consider that the Sacra- 

 mento really drains something like 15,000 square miles, before reaching 

 the city, we find no difficulty in accounting for the freshets without sup- 

 posing an extraordinary fall of water. In the five da3^s from the 5th 

 to the 9th of" March, tliere fell five inches of water at San Francisco. 

 Suppose the same quantity throughout the State, and four fifths of it to 

 sink into the earth, the remaining fifth, equal to one inch, running off, 

 and requiring an entire week in the drainage. With a channel at Sa- 

 cramento 200 yards wide, and a current of four miles an hour, the river 

 would be raised seventeen fed, and kept at that height a whole week! 

 With these data in mind, there is no difficulty in comprehending the 

 great effects of even moderate rains in producing freshets, especially 

 when the melting snows add to the supply. 



The table contained in my last article shows that thejiumber of days 

 entirely or nearly clear, from sunrise to sunset, in the year 1851, was 

 134. This is not very different from the Atlantic States. At Phila- 

 delphia the number varies from 100 to 140, with an average of 125. 



Owing to the many days that are partly clear, the number entirely 

 clear does not present a criterion of the proportion of clear weather. 

 By taking also into consideration the days that were clear in part, we 

 find, as the table exhibits, tlie proportion of clear weather to cloudy, in 

 the year, to be 262 to 103. The ratio at Philadelphia is about 220 to 

 145. The sky is therefore less clouded at San Francisco than on the 

 Atlantic border. 



I have already noticed the inconstant character of the clouds, the 

 sky being seldom completely clouded for 12 hours, even in the rainiest 

 period. The number of days in the year entirely cloudy, from the 

 rising to the setting of the sun, was 18. At Philadelphia 50 is a very 

 low number, and there are often 75. Seldom does any month of the 

 year elapse in the Atlantic States without one or more days perfectly 

 cloudy. At San Francisco there were but three such days in the six 

 months from May to October. On most of the 18 days set down as 

 entirely cloudy, the clouds were at times sufficiently broken to render 

 the sun visible. It is an extraordinary circumstance fi^r the sun to 

 make his day's journey without showing his face. 



The chilling mists of summer, conspiring wath the wind and dust, 

 leave on one's mind impressions not the most agreeable or evanescent; 



