48 A MONTANE RAIN-FOREST. 



From the four months' record of evaporation at Cinchona it is 

 possible to make a rough calculation of the total evaporation of the 

 year. The atmospheric humidity is the most important climatic ele- 

 ment in determining evaporation rate in the Blue Mountain region, 

 and the average humidity for the four months from August to November 

 is nearly the average for the year (84.9 as against 84.1 per cent). The 

 total annual evaporation may therefore be estimated as not far from 

 three times the amount for the months covered by the accompanying 

 readings. The total of the readings is 989.1 c.c., which may be placed 

 at 1,000 c.c. for the present purpose. The total annual evaporation 

 of 3,000 c.c. must be multiplied by 0.76, the factor by which the loss 

 of the cup is reduced to terms of the loss from a free-water surface in 

 a petri dish. The annual total is thus made about 2,250 c.c., again 

 keeping the calculation in round numbers. The diameter of the petri 

 dish is 94 mm., and the annual loss from its water surface per square 

 centimeter would be 32.6 c.c. The average annual rainfall at Cinchona 

 is 106 inches, or 271 cm. The total annual fall of rain per square 

 centimeter is therefore 271 c.c., which is to 32.6 c.c. as 8.3 is to 1. 

 The rainfall at Cinchona is therefore about eight times as great as the 

 possible evaporation. Since the evaporation at Cinchona was found 

 to be about fourteen times as great as that in typical Windward Ravine, 

 the ratio of evaporation to rainfall for the latter locality is 1:112, if 

 we take no account of the higher rainfall which undoubtedly exists on 

 the windward side of the Blue Mountains An accurately determined 

 ratio of evaporation to rainfall for this extremely hygrophilous habitat 

 would probably be near 1 : 140. 



AIR TEMPERATURE. 



Reproductions of some of the thermograph traces secured at Cin- 

 chona and in different natural habitats are shown in plates 23 to 28, 

 and a digest of the data given by these curves is presented in table 1 1 . 

 Although no two of the thermograph traces are strictly comparable in 

 the sense of covering the same interval of time, they serve to show the 

 character of the daily march of temperature, and to emphasize the 

 constancy of the temperature conditions not only throughout the day 

 but throughout the several habitats in which they were secured. Only 

 at Cinchona and in the Ruinate on the Leeward Slope was the average 

 maximum temperature above 70 F. On Sir John Peak the average 

 maximum was 60.5 F., which is higher than that of the Windward 

 Ravines over 1,000 feet lower in altitude, and identical with the maxi- 

 mum secured for Ridge forest at the lower altitude. The minimum 

 temperature at Sir John Peak is, however, carried somewhat lower 

 than that of Windward Ravines at lower elevations, in spite of the 

 records on the peak having been secured later in the spring than those 

 in the Ravines. 



