1832] 



Meteorological Observations. 



31 



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

 vation 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 

 sunset than at sunrise. At the Madras observatory, in 1832, 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 under- 

 taken by Col. Balfour at Calcutta, in the year 1784. We have also in 

 manuscript a diary kept by Mr. G. A. Prinsep, during 32 days of a voy- 

 age from Calcutta to Bombay, whence it appears that upon the ocean the 

 Barometer falls from 10 p. m. to sunrise — .022 

 rises from sunrise to 10 a. m. +.044 

 falls from 10 p.m. to 4 p.m. — .102 



rises from 4 p.m. to 10 p.m. +.080 

 on the other hand, the Berhampur register exhibits a constant rise 

 from 10 p. m. to 5 A. m. but as the corresponding- thermometrical register 

 is unfortunately not in our possession, we have been obliged to substitute 

 a correction from the means of the Calcutta register, and the results may 

 be in some measure erroneous : they cannot however be so far from the 

 truth as to reverse the apparent issue. At Seharanpur also the exis- 

 tence of a nocturnal tide is equivocal ; the following table exhibits all 

 that we can gather towards the elucidation of the point in India, ex- 

 pressing by minus signs the real tide, or fall of the barometer, from 10 

 p. m. to 5 a. m. and vice versS. 



Table VI. Nocturnal Oscillation of the Barometer from 10 P. M. to 5 A. M. 



reduced to 32° Fah. 



Month. 



January, 

 February, 

 March, .. 

 April, .... 



May, 



June, .... 



July, 



August, . . 



September, 



October, 



November, 



December, 



Means,. . .. 



Madras, 3 

 Jays in each 

 month. 



—.001 

 —.029 

 —.026 

 —.027 

 —.014 

 —.026 

 —.009 

 —.028 

 —.024 

 —.033 

 —.010 

 —.019 



— 021 



Berhampur, 

 from Dr. Rus- 

 sel's tables. 



+ .034 

 + .02G 

 + .009 

 + .088 

 + .020 

 +.012 

 + .000 

 +.014 

 + .011 

 + .009 

 +.009 

 +.027 



+.020 



Seharanpur, .Vera Cruz in 

 Dr. Royle's Mexico, by 

 observations.) Fray Juan. 



—.043 



+.018 



—.009 



+.009 



—.008 



—.002 



—.007 



+.008 



—.020 



+.005 



+ .039 



+.003 



—.005 



—.002 



—.016 



—.007 



+ .011 



—.012 



—.004 



—.021 



+.024 



+.001 



+.015 



—.023 



-.001 



-.002 



