OF THE ATMOSPHERIC TEMPERATURE. 



201 



In a few instances the means are derived only from 3 or 4 years, and to complete 

 the table means from a station adjacent to that heading the colnmn were introduced; 

 upon the whole, the table required the use of monthly records for an aggregate of 

 540 years. Notwithstanding the incidental irregularities in the successive values 

 of this table, they appear to point conclusively to an epoch between 1841 and 1850 

 • when the positive values reached a maximum, in other words, when the mean 

 temperature of February was the lower (or when the lowest temperature of the 

 year fell in that month). They also indicate, though with less certainty, a preceding 

 epoch about the beginning of the century, when the coldest epoch of the year fell 

 early in January, in which month it is again found at the present time. Such a 

 shifting in the epoch of greatest annual cold can only be of a periodic nature, and 

 we may, therefore, look forward in the course of a few years to a return motion. 



To elucidate the point, whether the epoch of maximum annual heat was 

 accompanied by a corresponding movement, a similar table was prepared contain- 

 ing the differences (J. — A.), a -j- sign indicating July warmer than August, a — sign 

 would indicate the reverse. The successive annual values of which this table is 

 made up were found to be much more irregular than the corresponding values for 

 the cold period, though the individual differences are smaller, a fact which might 

 have been anticipated from our knowledge of the greater variability of temperature 

 in winter when compared with that of summer. The parallelism of the movement 

 over large areas, also, is less distinctly pronounced in summer than in winter. 



Table of differences (J. — A.) for supposed change in epoch of the greatest annual heat. 













1 









a 



d 







•a - 



■5 



Epochs. 



U 3 

 II 



c 

 S 







C/2 



to 

 S 



> 



u 

 0" 



c 



§ 



1 





 U 



6 



> 



6 

 



1 









r 

















Q 







Q 



Q 



Q 



Q 



;, 







Q 







1781-85 













0.2 

















1786-90 









—1-7 





+ 1.2 



















1791-95 

















4-'2.8 



4-0.6 



















1796-1800 



4-'i'.i 







+ 1 



9 



4-1.9 



-f-i.3 



















iSoi-05 



-f-O.I 







4-1 



2 



4-1.8 



4-0.9 



















1S06-10 



4-0.2 



— o-S 





4-0 



8 



4-1.2 



4-1.2 





4-0.6 















iSn~i5 



+ 1.8 



+ 1.2 





+2 



5 



—0.7 



-fi.4 





4-2.9 















1816-20 



+ 1-7 



+ 1.8 





+2 



5 





+2.5 





4-1.2 







-f'i'.7 









1821-25 





+2.8 





+2 



4 





4-2.2 





4-1.2 



4-0.9 







+ 1 



7 





1S26-30 





+ 2.1 



4-'l'.2 



+2 



4 





4-0.6 





+ 2.8 



--O.7 





4-0.1 



-f4 



.0 



;; 



1831-35 





+ ■•7 



+3-0 



+2 



2 





+ 1.5 





+2.3 



4-0.7 



+•'0.6 



4-2.2 



+4 







-fi.5 



1S36-40 





+ 2.7 



+4-3 









-f3.o 





-h2.9 





4-2.2 



4-2.0 



-t-3 



9 



4-2.0 



1841-45 





—0.4 



—1.4 







+ I.S 



-fo.5 



— 0.5 



4-1.2 



4-"i.8 



4-1.0 



4-2.0 



+3 



4 



+3-5 



1846-50 





4-1.4 



+3-9 







4-2.8 



4-2.0 



4-0.6 



4-0.7 



-t-0.8 



— 1.2 



+ 1.2 



-f3 



.0 



4-2.0 



1851-55 





+4.1 











4-3-3 



+ 1.4 



+3.5 



4-0.6 



-i-1.7 



+ 2.3 



+4 







4-1. 1 



1856-60 





4-2.9 











-fi.9 



4-1.6 



+ZA 



-t-o.5 





+3-2 



+5 



7 



4-4-7 



1S61-65 















-t-i-S 



4-0.1 



0.0 



-fo.3 







-f3 



I 



+0.5 



1866-69 

















4-6.1 



4-4.6 













There appears to be no regular progression in any of the figures of this table 

 that could be ascribed as accompanying the singular anomaly of values between 

 1841-50, and even when means are taken for each five-year combination, the result 

 remains inconclusive. If there is any variation in the epoch of maximum heat, it 



26 March, 1875. 



