108 CLIMATE AND VEGETATION Of 



have, if sufficiently numerous, a value wlien properly reduced, 

 and are indispensable to the liorticulturist ; they give, witluH 

 certain limits, the difference of temperature due to the difference 

 of altitude for the month in which they are taken ; and if a few 

 days of several months, or a considerable portion of either equi- 

 noctial month (March or October), are spent at one place, the re- 

 sults give useful approximations to the mean annual temperature. 

 Tlie results thus obtained have been checked by ground tem- 

 peratures, taken by burying a brass tube 2 feet 6 inches to 3 feet 

 in exposed soil, sinking in it, by a string or tied to a slip of wood, 

 a thermometer whose bulb is well padded with wool. This, 

 after a few hours, indicates the temperature of the soil, which 

 has a definite relation to the mean temperature of the month, and 

 further, has an obvious practical application to the growth of plants. 

 Such a tube and thermometer I usually caused to be sunk 

 wherever I halted, if even for one night, except during the 

 height of the rains, which are so heavy that they communicate 

 to the earth a temperature sometimes above that of the air. I 

 cannot too confidently recommend this simple plan to travellers, 

 for the double purpose of getting an approximation to the mean 

 monthly temperature by a few observations, and of finding tlsat 

 of the soil. One such observation is worth a hundred of such 

 as are paraded in the works of travellers, as taken with a ther- 

 mometer hung inside a tent, or to a tree, &c., the majority of which 

 are not worth recording. With regard to other observations, 

 the wet bulb and barometer were invariably registered with the 

 temperature, and the minimum spirit thermometer set every night. 

 Of maximum thermometers I tried many, but never kept one 

 long in working order. A radiating thermometer in a parabolic 

 reflector, and others placed on cotton and grass, were frequently- 

 exposed, and I found no material difference between that laid 

 on cotton and tiiat in the reflector. The black-bulb thermometer 

 was often observed, and a large series of actinometer obser- 

 vations taken ; these have not been computed, nor the dew-points 

 from the wet-bulb temperatures, the correction (p-f) always 

 required at considerable elevations being laborious. I have, 

 however, computed as many as to convince me that the cultivator 

 may assume the mean state of humidity given for Darjiling, 

 which I have computed (on monthly means of 1835 observa- 

 tions), as applicable to both the upper zones — the difference of 

 humidity between 7000 and 14,000 feet being that the excessive 

 rain-fall of the lower station, and great capacity for moisture 

 of the lower warmer strata, do not extend proportionally to the 

 upper, whose cooler atmosphere, however, holds less vapour in 

 suspension. In all tluee zones the atmosphere is generally well 

 loaded with humidity. 



