I^ GENERAL INTRODUCTION. 



ing January. February, and March. Notwithstanding- these facts, 

 diseases of the luno;s are rare amono- the inhabitants, and even the 

 severe winters have proved of benefit to those consumptives that have 

 remained here throughout the entire year. 



The mean annual rain-fall exceeds that of most portions of the 

 State, and is estimated by Mr. Colvin, from the available data, to be 

 45.18 inches (1,149 mm.) for the entire region. The mean annual rain- 

 fall over the whole State is 41.94 inches (1,063 mm.).'-' 



There are two elements that tend to increase the humidity of this 

 region : ist. its mountainous character, for mountains always act as 

 condensers of moisture; and 2d. its heavy covering of forests, for 

 dense vegetation protects the underlying soil and rock from the direct 

 action of the sun, and keeps the temperature lower — thus favoring 

 condensation and the precipitation of excess moisture. 



"A deciduous tree, during the season when in foliage, is constantly 

 drawing from the earth and giving off from its leaves a considerable 

 amount of moisture, and in some cases this amount is very great. 

 This change of state, from a fluid to a gaseous condition, is a cooling 

 process, and the air near the surface, being screened from the sun and 

 from the winds, becomes by this means so humid, that a rank suc- 

 culent vegetation often springs up and thrives, which in an open field 

 would wither and perish in an hour."f 



Now it is well known that there is, in nature, no such thing as a 

 perfectly dry atmosphere, for at all times, and in all places, it is laden 

 with less or more aqueous vapor in a state of suspension. The higher 

 the temperature the greater the capacit\- for carrying moisture, and 

 consequently the more moisture required to produce saturation — by 

 which term we understand the maximum quantit}' of watery vapor 

 that a definite amount of atmospheric air can contain at any given de- 

 gree of temperature. No evaporation whatever can take place from any 

 surface in a saturated atmosphere, and an)- cooling of such an atmos- 



* Meteorology of New Vork Stale, Second Series, F. 15. Hough, 1S72, p. ix. 

 f Hough's Report on Forestry, 1S78, p. 289. 



