HYDROLOGY OP NEW YORK 



47 



of the United States, and has since been operated as a bureau of 

 that department. Complete observations are taken at the six 

 original stations established by the United States Signal Service, 

 including barometer, temperature, dewpoint, relative humidity, 

 vapor pressure, precipitation, wind, cloudiness and electrical 

 phenomena. Generally, the Regents and the Smithsonian obser- 

 vations only included temperature and precipitation, although 

 there were a few exceptions where barometer and wind were 

 taken. The Meteorological Bureau also generally confines itself 

 to temperature and precipitation, except that at the central office 

 at Ithaca, and at a few other places, barometer and cloudiness 

 are taken. The same statement applies to the work of the 

 Meteorological Bureau as carried on under the direction of the 

 United States Department of Agriculture. 



The average annual temperature is generally taken as decreas- 

 ing with altitude at the ratio of 1° F. to every 300 feet of eleva- 

 tion, the rate being somewhat below this average in winter and 

 above it in summer. Au approximate determination for the State 

 indicates that the. rates of decrease are 0.3° F. per hundred feet 

 elevation for the winter, and 0.4° F. per hundred feet for the sum- 

 mer. For the mountains of northern New York a much smaller 

 variation than 0.3° F. appears to hold for the winter months. 



The intimate relation which exists between air circulation and 

 precipitation in New York is one of the most interesting facts 

 to be noted. Owing to lack of moisture in the continental inte- 

 rior, northwest winds in the spring, summer and fall are essen- 

 tially dry. In winter their dryness proceeds from low tempera- 

 ture and consequent small vapor-carrying capacity. The winter 

 precipitation is due almost entirely to storm areas passing either 

 actually across or in the vicinity of this State and deriving their 

 supply of vapor from the inflow of moist air which they induce, 

 either from the Atlantic ocean or from the Gulf region. 



The winter months — December, January, and February — have 

 somewhat less precipitation than either of the other seasons, 

 although in the vicinity of the Atlantic coast, on the southwestern 

 highlands of the State, and in the region of the Great Lakes the. 

 winter precipitation is relatively large. 



