STATE AGRICULTURAL SOCIETY. 395 



larger amount of precipitation of moisture, in the form of snow, during the 

 Winter months. 



It will he observed that the mean temperature for twenty years is 50.3 

 F. This, however, should not mislead the reader, since a close analysis 

 will at once indicate that the amount of heat is by no means equably dis- 

 tributed, and this would be still more apparent could the columns and 

 pages of individual observations be presented here. October, as regards 

 temperature, is the typical month of the year. The mean temperature of 

 this month for twenty years differs but two degrees from the mean annual 

 temperature for the same period. 



The highest temperature observed in any one month was 100° F., in 

 July, 1876; and the next highest, 99°, in August, 1870 and 1879. The low- 

 est temperature in any one month was 19° below zero, in February, 1884. 

 Absolute range during a period of twenty years, 119°. July and August 

 are the hottest months in the year, and January, February, and December 

 the coldest months. Frosts occur late in the Spring and early in the Fall. 



A study of the tables, especially of No. 3, will indicate that a striking 

 peculiarity of this climate is the extreme range of temperature, particularly 

 noticeable during the months of July, August, September, and October. A 

 daily variation of 50° is not uncommon, and even a daily range of 62° has 

 been observed in August. 



This excessive diurnal variation is intimately connected with the dry- 

 ness of the atmosphere. The absence of watery vapor permits the surface 

 of the earth to be rapidly heated by the rays of the sun, and likewise favors 

 rapid radiation after the maximum is reached. As a result we have often 

 very warm days, and excessively cool nights — a very important feature of 

 this climate from a sanitary point of view. In my discussion of some of 

 the prevalent diseases of the community, I will have an opportunity to 

 point out the relations of cause and effect. It may be, because the greater 

 portion of my professional life has been spent at mountainous posts on the 

 middle and northern plateau, where extreme ranges of temperature are 

 especially observed, that I have become oblivious to other conditions by 

 assuming that the great changes in temperature are the chief cause of a 

 certain class of diseases. I shall endeavor, however, to present the facts 

 and opinion unbiased, not doubting for a moment that elsewhere other 

 factors may and do enter into the production of disease, and that I may be 

 entirely wrong in my interpretation of the relations between this climate 

 and some of the prevalent diseases. 



2. Precipitation. 



An analysis of the meteorological tables with reference to the amount of 

 precipitation, will indicate that the "rainy season" during the Winter and 

 Spring months is fairly well defined, and the amount of precipitation in 

 the form of snow is frequently excessive. 



During the Summer and Fall, or the "dry season," the amount of pre- 

 cipitation is hardly appreciable ; whole months often pass without bringing 

 us a shower. Dews are rarely, if ever, observed. When it is sufficiently 

 cool at night to condense the little moisture that is in the atmosphere, with- 

 out precipitation in the form of rain or snow, it is deposited in the shape 

 of frost. 



The dryness of the atmosphere is partly accounted for by the elevation, 

 but more especially the geographical location of the valley, since the pre- 

 vailing winds from the west naturally condense most of their moisture 

 upon the western slope of the Sierra Nevadas; but there seems to be a 



