1832.] 



Meteorological Observations. 



33 



TABLE VIII. Mean Barometric Pressure of Aqueous Vapour in the Air during the 

 same period, deduced from Table VII. and Buttons Table of Aqueous Tensions. 



Month. 



Sunrise. 



h. m. 



9 40 a m. 



Noon. 



'(. m. 

 2 50 p. no. 



4 p. m. 



Sunset, 



January, .... 

 February, . . 



May, 



August, .... 

 September, . . 

 October, .... 

 November, . . 

 December, . . 



inch. 



0,336 

 .513 

 .703 

 .846 

 .904 

 .994 

 .909 

 .911 

 .892 

 .840 

 .588 

 .465 



inch. 



0.336 

 .476 

 .590 

 .792 

 .931 

 .980 

 .908 

 .920 

 .889 

 .788 

 .495 

 .456 



inch. 



0.300 

 .413 

 .546 

 .721 

 .911 

 .975 

 .900 

 .916 

 .859 

 .773 

 .449 

 .424 



inch. 



0.288 

 .407 

 .504 

 .649 

 .911 

 .985 

 .903 

 .914 

 .869 

 .738 

 .424 

 .413 



inch. 



0.275 

 .300 

 .500 

 .690 

 .902 

 .995 

 .901 

 .897 

 .887 

 .760 

 .432 

 .404 



inch. 



0.275 

 .403 

 .535 

 .755 

 .941 

 .987 

 .910 

 .926 

 .861 

 .814 

 .543 

 .485 



Means-, . . 



.751 



.713 



.682 



.667 



.660 



.710 



It is here observable, that besides the apparent drying of the air 

 caused by the increase of heat during the day, it actually seems to be- 

 come less loaded with moisture from sun-rise to 3 p. m. to the extent 

 of about 10 per cent. : this is not easily explained without recourse to 

 suppositious errors of the instruments or of the formulae of calculation ; 

 for it is difficult to imagine that the vapour should rise independently 

 of the air with which it is mingled ; or if it does rise, that it should fall 

 again so rapidly, to resume its place in the lower atmosphere on the fol- 

 lowing morning. — It might be expected a priori that where fogs prevail- 

 ed in the morning, or where dew was deposited, the pressure of aque- 

 ous vapour measured in the morning would be less than in the middle 

 of the day ; and the appearance of a contrary result, if it does not point 

 to a probability of errors in the instruments, or in the experiments 

 upon which the calculations are grounded, tends at any rate to show 

 that much remains to be done to explain facts, and to place this branch 

 of meteorological incmiry upon a firm basis. 



It is however some satisfaction to know, that the register, kept at the 

 surveyor general's office, is in this, as well as other respects, superior to 

 most of those published in the scientific journals of England, where tlie 

 column devoted to the hygrometer is generally a mere mass of figures,* 

 convertible to no useful purpose. It is to be hoped, that all who regis- 

 ter their observations in India will adopt the same kind of hygrometer, 

 namely a thermometer with a bulb projecting from the scale, and 

 covered with a wetted muslin bag. Its indication should first be 

 carefully compared with the dry thermometer, and corrected for any 

 errors of division. P. 



