ATMOSPHEROLOGY.-rTEMPERATURE. 351 



through the course of twelve successive months, sel- 

 dom differs from the general mean temperature, as 

 derived from the observations of a great number of 

 years, more than two or three degrees *. 



The mean temperature of any single month, can- 

 not be supposed to be equally uniform ; since the 

 uncommon prevalence of a south wind in winter, or 

 a north wind in summer, may cause the particular 

 month in which such winds occur, to be considerably 

 colder or warmer than the standard. This, however, 

 does not differ so widely from the general mean of 

 that month as might be expected f . 



• From the meteorological register kept at the apartments 

 of the Royal Society, we find, that in twenty years, included 

 between 1795 and 1814, the mean annual temperature was 

 50*. 4. Now, in eight of these years, the mean temperature 

 was within 0". 5, or half a degree of the general mean ; in thir- 

 teen years, within one degree ; in sixteen years, within two de- 

 grees ; and, in no instance, differed more than two and a half 

 degrees from the general mean. Hence in similar climates, 

 by one year's thermometric observations, we derive the mean 

 temperature thereof, within 2^°, by ^ probability of at least 

 twenty to one: that is, it is more than twenty to one, in the 

 way of chance, but the annual mean temperature ascertained, 

 is within 2|° of the general mean, or standard temperature ; 

 four to one that it is within 2° ; three to two that it is within 

 !•; and two to three, that it is within half a degree. 



t The mean temperature in London, of the months of March, 

 April, May, June, July, and August, never, in one instance, dif- 

 fered so much from the general mean temperature of the rela- 

 tive month, as 5° ; and February, October, and November, ne- 

 ver more than 6°; but the greatest difference in December, 

 amounted to 8°.4 ; and in January, to 11°. 4. — (Phil. Traps^ 

 1796 to 1815.) 



