242 MR. G. V. VERNON ON MEAN MONTHLY 



29*780 inches, which, corrected for an altitude of 123 feet 

 above the mean sea-level, and assuming the mean annual 

 temperature to be 50 F., gives us 29*912 inches as the 

 mean yearly value reduced to sea-level. 



If we take the complete period of the last eleven years, 

 we have a mean reading of 29*838 inches, which is 0*074 

 inch below the value given for the entire period 1849 

 to 1872. 



In the earlier series the month of August was generally 

 wanting in the observations, except for a few years ; but 

 this month, having a reading generally in excess of the 

 yearly value, would tend, if any thing, to make the annual 

 value somewhat higher ; and the result would tend to show 

 that during recent years the pressure has been lower than 

 during the earlier part of the series. 



The variation between the highest and lowest mean 

 yearly readings during the last eleven years is 29*828 

 inches (1870) and 29*624 inches (1872), or equal to 0*204 

 inch : this would appear greater than probability would 

 point out, 1872 having had an exceptionally low mean 

 reading; leaving 1872 out, we have a difference of o* 118 

 inch between 1870 and 1866. 



Looking at the mean monthly values, we find that the 

 maximum occurs in June and the minimum in January. 

 The order, beginning with the minimum, is January, Octo- 

 ber, March, December, November, September, February, 

 July and April equal, also May and August equal. If 

 fine weather depends upon barometric pressure, the above 

 shows that May and August should be the finest months, 

 as a rule, and January and October the worst. May is 

 next to the driest month April ; and October bears off the 

 palm for being the wettest, at least in this district. 



The remarkable year for rain 1872 would appear to have 

 been also remarkable for deficient atmospheric pressure, 

 as the table annexed will show, every month except August 



