343 



The Meteorology of the Plains 



[April 



Diurnal Oscillations of the Barometer and Thermometer at 

 Calcutta, ivith Comparative Observations at other places. 



Month. 



Barometer at 32". 



- >3 



>^ '-' 



Thermometer. 



C 



3T3 



-a ^ S 



0- S 



»-• CD •,-< 



rt i!; aj 



O) X.2 



.(DC 

 <U C O 



S ° S 



s s ^ 

 ^ a ^ 



Januarj' ^ 



February 



March 



Apiil 



Way 



June 



July 



Au^'ust : . 



September 



October 



November 



December 



Mean tide. . 



Inch. 



Inch. 



loch. 



Inch, ilnch. 



Deg. 



Deg. 



Deg. 



Deg. 



Deg. 



•072 



•144 



•123 



•097 



•103 



11-0 



9-4 



20-7 



17-8 



'24-5 



•070 



•126 



•117 



•103 



•093 



10-0 



16^8 



18-5 



19-2 



21^0 



•076 



•107 



•125 



•121 



•146 



7^0 



20-8 



14-0 



20-7 



26-0 



•081 



•110 



•124 



■125 



•107 



9-0 



20-9 



14-6 



23-2 



sro 



•081 



•113 



•115 



•124 



•160 



9-0 



20^4 



13-7 



21 ■« 



38-0 



•092 



•136 



•095 



•113 



•178 



9-0 



9-0 



7-6 



16-1 



31-5 



I -097 



•133 



•090 



■077 



•103 



7-0 



6-6 



6-1 



9-0 



15^3 



•105 



•109 



•099 



■088 



•079 



7^0 



8^8 



5-9 



8-3 



1P5 



•094 



•145 



•101 



•103 



•123 



6-0 



7-8 



6^2 



10^3 



13^0 



•068 



•144 



■110 



•100 



•120 



8-0 



5-0 



8^4 



18^1 



31 ■ 5 



•071 



•127 



•107 



■107 



■147 



8-0 



6-7 



13-4 



16-8 



29-3 



•071 



•126 



•114 



•098 



•124 



9-0 



8-5 



17^1 



16-3 



17^5 



•081 



•126 



•no 



•105 



•120 



8-5 



10^6 



12-2 



16-6 



24^3 



With due allowance for the difference of sensibility in the instru- 

 ments, the above table shews that the average diurnal tide of the baro- 

 meter between the Equator and 30° north latitude, exceeds one-tenth of 

 an inch, and that it is progressively greater as the variation of tempera- 

 ture during the day is also greater. With regard to the nocturnal tide 

 of the atmosphere, the Calcutta tables afford us no data, for want of an 

 observation at 10 p. m., the hour of the supposed maximum at night; 

 all that is indicated therein is, that the barometer is constantly lower at 

 sun-?et than at sun-rise. At the Madras Observatory, in 1823, a series of 

 horary observations was made for three days in each month, which 

 seems to establish the fact of a night-tide beyond a doubt to the extent 

 of .04 inch ; when, however, the corrections for the temperature of the 

 mercury are applied, this amount is reduced to two-hundredths of an 

 inch, which is one- fifth only of the diurnal tide. 



" The same result is obtained from a month's horary observations, 

 undertaken by Col. Balfour, at Calcutta, in the year 1784. At Saharun- 

 pore, also, the existence of a nocturnal tide is equivocal: the following 

 table exhibits all that w^e can gather towards the elucidation of the 

 point in India, expressing by minus signs the real tide, or fall of the 

 barometer, from 10 p. m. to 5 a. m., and vice vei-sdj* Mr. Prinsep con- 

 cludes by saying, " There is still sufficient ambiguity respecting this 



