CLIMATOLOGY OF RAIN-FOREST REGION. 



13 



It may be noted that the annual minimum falls in May, three months 

 after the minimum for the air; the annual maximum in September, one 

 month after that for the air. The correspondence of the annual mean 

 temperature of the soil at 6 feet with that of the air to within 1 is here 

 confirmed: 61.6 -1 = 60.6, as compared with 60.8, the mean of the 

 air readings. 



HUMIDITY AND FOG. 



The humidity record for Cinchona consists of daily readings of 

 stationary wet and dry bulb thermometers at 7 a. m. and 3 p. m. A 

 number of comparisons of wet-bulb readings with sling psychrometer 

 readings were made in 1906 and 1909, showing that the wet-bulb readings 

 are as a whole from 1.5 to 3 per cent too high, owing to the stationary 

 character of the wet-bulb apparatus. Table 5 gives the monthly means 



TABLE 5. 



for fifteen years (1891 to 1905, inclusive), the mean of the two daily 

 readings being taken as the daily mean. The reduction to percentages 

 has been made with a table prepared by Mr. W. Maxwell Hall, and no 

 correction for the inherent error of the instrument has been made. 



A general correspondence may be seen, as is to be expected, between 

 the annual curve of humidity and that of rainfall (fig. 1). 



The high humidities prevalent at Cinchona and throughout the Blue 

 Mountains are due in great part to the high percentage of cloudiness 

 and the frequency of fog. On the northern slopes of the range at all 

 elevations from below 4,500 feet to the summits of the highest peaks 

 fog is prevalent from 10 a. m. to 4 p. m. on a very high percentage of 

 the days in all months except February, July, and August. On the 

 southern slopes the amount of fog is much less. Fog at night is rather 

 exceptional, occurring more often, in my own observation, on the 

 summits of the Main Ridge than below 5,800 feet. 



RAINFALL. 



The rainfall readings at Cinchona have been made from a Negretti 

 and Zambra gauge of the ordinary type from day to day as the fall 

 required. Those at New Haven Gap and Blue Mountain Peak were 

 made on the last day of each month, no allowance being made for 



