32 



Meteorological Observations. 



[Jan. 



The last column is taken from the manuscript observations of Fray 

 Jaun, at Vera Cruz, in 1817-18, in the possession of a friend : the 

 latitude of that place, 19° N., should make the results applicable here. 



There is still sufficient ambiguity respecting this second tide, there- 

 fore, to render further enquiry necessary ; and it would be desirable to 

 employ a barometer for the purpose, which should not require to 

 have any correction applied for the temperature of the mercury; this 

 might be easily effected by enclosing the barometer tube in an outer 

 tube of the same length, also filled with mercury, upon the surface of 

 which the scale might float. 



Hygrometry. 



The Calcutta tables afford sufficient data for calculating the 

 state of the air with respect to moisture, whenever the temperature 

 of an evaporating surface can be converted with certainty into equiva- 

 lent expressions of the more obvious phemomena of Hygrometry, such 

 as the tension or relative dryness ; or the absolute quantity of aqueous 

 vapour contained in a given space — The first of these points may be 

 found within the limit of 2 or 3 per cent by the tables published in the 

 first volume of the G leanings : — and/ihe second may easily be calculated 

 therefrom by the formulae of Dalton or Ure — In the following tables 

 this has been done, and the uniformity of the results is satisfactory 

 enough. August is the most damp month of the year to the sense ; but 

 June is the month in which the atmosphere is really loaded with the 

 greatest weight of aqueous vapour. January is in every respect the 

 driest season of the year, but the drought at Calcutta naturally falls 

 far short of what is experienced at Benares and Seharanpur, where the 

 depression of the moistened thermometer sometimes exceeds 35 degrees. 



Table VII. 



Depression of the Wet-bulb Thermometer and deduced Tension of Va- 

 pour in the atmosphere, at Calcutta, 1829-30-31. 





Sum 



•ise. 



9 41 



1 a. in. 



Noon. 



2 50 p. m. 



4 p. in. 



Sunset. 



Month. 



















Dep. 

 2°.3 



Ten. 

 .82 



Dep. 



Ten. 



Dep. 

 13°.l 



Ten. 



Dep. 



Ten. 

 .31 



Dep. 

 14 C .4 



fen. 

 .32 



Dep. 



9°.3 



Ten. 



January, .... 



8°.4 



.51 



.37 



15°.9 



.50 



February. . . 



1 .6 



.87 



8 .5 



.56" 



12 .4 



.41 



14 .4 



.38 



13 .9 



.39 



11 .1 



.47 



March, .... 



1 .9 



.89 



8.7 



.59 



12 .6 



.47 



14 .2 



.41 



14 .1 



.41 



10 .7 



.51 



, April, 



1 .4 



.94 



8 .1 



.66 



11 .7 



.53 



13 .9 



.46 



12 .7 



.50 



8 .1 



.64 



* May, 



1 .8 



.92 



7 .3 



.69 



9 .8 



.62 



10 .8 



.58 



9 .7 



.61 



6 .0 



.73 



June, 



1 .6 



.92 



1 .4 



.78 



6 .6 



•71 



6 .6 



.73 



5.2 



.76 



.5 



.83 



July, 



1 .9 



.90 



4 .6 



.79 



5 .5 



.75 



5 .5 



.74 



5 .0 



.77 



3 .5 



.83 



August, .... 



1 .6 



.93 



4 .4 



.80 



5 .4 



.77 



4 .9 



.77 



4 .8 



.78 



3.1 



.85 



September, . . 



1 .7 



.91 



5 .3 



.76 



6 .5 



.71 



5 .8 



.73 



5 .2 



.76 



3 .8 



.81 



October, .... 



1 .5 



.92 



6 .1 



.71 



8 .0 



.65 



8 .6 



.63 



7.4 



.66 



4 .3 



.79 



November, .. 



2 .8 



.85 



9 .0 



.55 



12 .3 



.44 



13 .9 



.40 



12 .6 



.43 



8 .1 



.59 



December, .. 



2 .4 



.83 



.892 



7 .4 



.59 



10 .8 



.47 



12 .5 



.43 

 .547 



11 .3 



.44 



.570 



6.9 



.61 



Mean Tension 



.665 





.577 







.680 



