xii 



APPENDIX. 



HYGROMETRY. 

 The instruments used in measuring. the evaporation and rain were described upon 

 a former occasion:* their performance has been very satisfactory, and the column 

 of Professor Leslie's Atmometer, I think, points out some respects in which the lat- 

 ter instrument seems inferior to my own. * Where the evaporation was very rapid 

 the porosity of the earthen bulb was inadequate to the supply (although I always 

 -used distilled water) and when the air took up but little moisture, it was impossible 

 to prevent the accumulation of a large drop of liquid under the bulb which either fell, 

 or increased the evaporating surface. 



By two months comparison I found that the evaporation from a large vessel was 

 just one-fourth less than from my small cup, so that the general annual evaporation 

 amounts to fifty inches. 



The mean temperature marked by the wetted bulb thermometer agrees almost 

 exactly with the mean lowest daily temperature, one being 68° 92" the other 08° 88" 

 and this is 9 degrees below the mean daily heat. In the hot winds 1 have frequently 

 observed a difference of more than 30 degrees between the dry and wet thermometers. 



The quantity of rain in 1823 was so much greater than usual, that it can form no 

 basis for calculation. In 1819 there fell but 30 inches at a small distance from Be- 

 nares, and "I should think in general that there must be less here than in Bengal. Mr. 

 James Kyd of Calcutta favored me with the result of a register kept by himself with 

 a reservoir of 100 square feet area which for comparison's sake I here subjoin : 



Month. 



October, 1821, ... 

 November, ...,,. 

 December, 



January, 1822, . . , 

 February, ...... 



March, 



April, ........ . 



»f une, 



July, .... . 

 August, .... 

 September, . 



Rain. 



3.00 

 0.00 

 

 









 



1 



12 

 9 



2 

 . 3 



Bain 33 



Evaporation 

 9 9.^ 



00 

 00 

 00 

 00 

 00 

 12 

 63 

 50 



50 

 00 



85 

 02 

 8? 

 75 



25 inch. 



Evap. 34.09 inches. 



See the accompanying plate and description,, 



