1858.] Meteorological Observations on Parisnatli Hill. 



41 



the rain is falling. "Widely spread and continuous falls of rain are 

 generally accompanied with a falling or rising of the barometer, de- 

 pending on other primary causes, which would screen from observa- 

 tion the similar or contrary effect of the rainfall. But a very slight 

 diminution of pressure by condensation extending simultaneously 

 over many degrees of longitude, and following the meridian as far as 

 the sun rises and sets once every 24 hours, is much more likely to be 

 felt, as it could not possibly be compensated for in a short space of 

 time. Its effect, if not great, must be constant, and will be found 

 in a smaller mean pressure during the night, than during the day. 



The tropical regions, where the time of sunrise, about 6 in the 

 morning, varies throughout the year at furthest about an hour and 

 a half would be best adapted to show such a difference, if it is great 

 enough to cause a visible depression of the barometrical column. I 

 have before me. the observations made in 1849 and 1850 at the 

 Colaba Observatory in Bombay and those made at Calcutta 

 Observatory in 1856. At Bombay the mean barometric pressure 

 in the curve of the hourly means of every month will fall very 

 nearly upon 6 a. m. and at Calcutta between 5 and 6 a. m. In- 

 cluding for the mean of the day the readings from 6 a. m. to 5 p. m. 

 and for that of the night from 6 p. m. to 5 a. m. the pressure of 

 the day always shows a slight excess over that of the night, as may 

 be seen from the following table. 



Table XIII. — Excess of the barometric pressure during the day over 

 that during the night. In Inches. 



Bombay. 



Jan. 



Feb. 



March. 



April. 



x\lay. 



June. 



1849 

 1850 



Mean. 

 Calcutta. 

 1856 



0.011 

 0.012 



0.011 



0.021 



0.018 

 0.016 



0.017 



0.029 



0.022 

 0.019 



0.020 



0.029 



0.015 

 0.019 



0.017 



0.029 



0.016 

 0.021 



0.018 



0.017 



0.009 

 0.01 1 



0.010 



0.005 



Bombay. 



July. 



August. 



Sept. 



Oct. 



Nov. 



Dec. 



Year. 



1819 

 1850 



Mean. 

 Calcutta. 

 1856 



0007 



0.008 



0.007 



0.003 



0.008 

 0.013 



0.010 



0.006 



0.014 

 0.009 



0.012 



0.015 



0.007 



0.U09 

 0.008 

 0.015 



0.009 

 0.012 



0.010 



0.009 



0.011 

 0.014 



0.012 



0.017 



0.012 

 0.013 



0.012 



0.015 



