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Appendix F. DISTRIBUTION OF TEMPERATURE. 407 



The mean daily range of the thermometer at 7000 feet is 13° in 

 cleared spots, bnt considerably less in wooded, and certainly one-third 

 less in the forest itself. At Calcutta, which has almost an insular 

 climate, it amounts to 17° ; at Delhi, which has a continental one, 

 to 21° 6 ; and in London to 17° 5. At 11,000 feet it amounts to 

 about 20°, and at 15,000 feet to 27°. These values vary widely in 

 the different months, being much less in the summer or rainy months. 

 The following is probably a fair approximation : — 



At 7,000 feet it amounts to 8°-9° in Aug. and Sept., and 17° in Dec. 

 11,000 „ „ 12° 



15,000 „ „ 15° 



London „ 20° 



The distribution of temperature throughout the day and year 

 varies less at Dorjiling than in most mountainous countries, owing 

 to the prevailing moisture, the effect of which is analogous to that 

 of a circumambient ocean to an island : the difference being, that 

 in the case of the island the bulk of water maintains an uniform 

 temperature .; in that of Dorjiling the quantity of vapour acts directly 

 by interfering with terrestrial and solar radiation, and indirectly by 

 nurturing a luxuriant vegetation. The result in the latter case is a 

 climate remarkable for its equability, and similar in many features 

 to that of JSTew Zealand, South-west Chili, Fuegia, and the damp west 

 coasts of Scotland and Ireland, and other countries exposed to moist 

 sea winds. 



The mean temperature of the year at Dorjiling, as taken by 

 maxima and minima thermometers # by Dr. Chapman, is nearly the 

 same as that of March and October : January, the coldest month, 

 is more than 13° 4 colder than the mean of the year ; but the 

 hottest month is only 8° 3' warmer than the same mean : at Cal- 

 cutta the months vary less from the mean ; at Delhi more ; and in 

 London the distribution is wholly different ; there being no rains to 

 modify the summer heat, July is 13° hotter, and January 14° colder 

 than the mean of the year. 



* The mean of several of the months, thus deduced, often varies a good deal 

 from the truth, owing to the unequal diurnal distribution of heat ; a very few 

 minutes' sunshine raises the temperature 10° or 15° above the mean of the day; 

 which excessive heat (usually transient) the maximum thermometer registers, 

 and consequently gives too high a mean. 



