508^ 



Meteorological Observations 



[Nov. 



the air. There is a less quantity of aqueous vapour in a given quantity 

 of air in January than in May, but the difference of temperature 

 makes the drying power of the air in the latter month superior to that 

 in the former. I find by a rough calculation that the weight of aque- 

 ous vapour in a cubic foot of air varies from 3-3 grains in January to 

 10.3 in August. Comparing the driest month at Dehli with the driest 

 in Calcutta, I find the ratio as 5 to 3 nearly : the dampest month is 

 nearly the same at both places, and the mean of the year as 5 to 4 

 nearly : I should have expected a much greater difference. 



/ D l • 28S \ 

 I have added a table of the factor y 5-84 — s ) for finding the 



dew point from observations of the temperature of the air and that of 

 the wet thermometer ; also the table of the force of vapour which I 

 have used in my reductions : should these be thought worth printing, 

 it will be as well to give an example of their use to prevent misconcep- 

 tion. Suppose the temperature of the air 100°, that of the wet ther- 

 mometer 70° .•. D = 30°, the barometer standing at 27*0 inch j required 

 the dew point and comparative tension? 



For wet thermometer 70° and D = 30° Table IV. gives -402 

 For barometer 27.0 inch, deduct "402 X '1= "040 



Force of vapour at 70° 



■362 

 •723 



Dew point 49°.9 — force of vapour answering thereto = "361 log. = 9'55751 

 Force of vapour at temp, of air 100° = 1'874 colog. = 972723 



Comparative tension = 0.193 = 928474 



Table I. Barometer reduced to 32°, and Temperature of the external Air observed 



at Gurgaon. 















Monthly 



Elevation of 



Year and 



10 A. M. 



4 I 



. M. 



Mean. 



Dally 



difference 



Gurgaon 



Month. 











range of 

 Bar. 



from 

 mean. 



above Cal- 





Bar. 



Temp. 



Bar. 



Temp. 



Bar. 



Temp. 







in. 







in. 







in. 



O 



in. 



in. 



Feet. 



May, 1829. 



28.832 



100.6 



28.712 107.6 



28.772 



104.1 



.120 



— .182 



868 



June, .... 



.813 



96.1 



.714 100.5 



.763 



98.3 



.099 



— .191 



841 



July, 



.717 



84.0 



.646 



87.0 



.682 



85.5 



.071 



— .272 



855 



August,... . 



.791 



83.9 



.711 



85.8 



.751 



84.8 



.080 



— .203 



803 



September, 



.882 



86.6 



.798 



91.7 



.840 



89.2 



.084 



— .114 



807 



October, . . 



29.034 



84.5 



.955 



91.1 



.995 



87.8 



.079 



— .041 



808 



November, 



.223 



72.7 



29.143 



79.1 



29.183 



75.9 



.080 + .229 



750 



December, 



.255 



62.4 



.158 



71.3 



.207 



66.8 



.079 +.253 



771 



Jan. 1830. 



.230 



66.0 



.140 



74.9 



.185 



70.5 



.090 + .231 



854 



February, 



.153 



69.8 



.067 



76.0 



.110 



72.9 



.086 



+ .156 



813 



March, . . 



.052 



77.3 



28.963 



83.4 



.008 



80.4 



.089 



+ .054 



814 



April, .... 



•• 



•• 



•• 



•• 



-• 



•• 



•• 



•• 



•• 













28.954 





.089 





817 



