THE ROYAL SOCIETY, AND AT THE ROYAL OBSERVATORY, GREENWICH. 585 
By taking' the means of the numbers in each column without respect to sign, we 
find that the variability of temperature is greatest in the winter months ; its mean 
value in January is 3°'l ; in both February and March is 2°‘6 ; in April is 2°'3 ; in 
May and June is 2°'0 ; in the months of August, September and October, whose tem- 
peratures are the steadiest, it is 1°'9 ; in November it is 2°’0, and in December it is 
S°'l, as in January. 
The numbers in the preceding Table very clearly show that causes exist at different 
times, which raise or depress the temperature, and which continue through long 
periods. 
As in the distribution of the positive and negative signs in the space of seventy- 
nine years, we perceive a gradual increasing preponderance of the positive signs over 
the negative signs, it seems that the temperature of the climate during this period has 
increased. 
As the mean results from so long a series of observations may be considered as 
true, having the advantage of being free from errors of observation and from those 
arising from imperfect instruments, we may really consider the numbers in the above 
Table as abnormal values ; yet as it seems most desirable to have those at the beginning 
of the series confirmed by the description of each year, made without instrumental 
means, for this purpose, as well as for the comparison of the character of the climate 
at the beginning- and at the end of the series, I have collected the following brief 
particulars of every year till that of 1800 ; after this time the general characters of the 
years are well known. 
1771- — There were frequent and very sharp frosts till April 20. On February 12 
the reading of the thermometer was as low as 4° ; the month of May was warm ; the 
summer was cool and dry; October was a wet and windy month, and the weather 
was mild to the end of the year. The severe weather of the beginning of the year 
caused a bad seed time, and the harvest was very late. 
1772. — The beginning of the year was mild ; from the middle of January frosts and 
great snows were frequent, and continued to the middle of March. The summer was 
very fine ; the autumn was mild but wet, and there was no frost till December 22. 
1773. — With the exception of the latter part of February, which was stormy and 
wet, there was much fine weather till the beginning of May; then many mornings 
were frosty, after which heavy rain fell frequently till June. The summer was fine; 
the autumn was wet. There were sharp frosts at the end of November and at the 
beginning of December. 
1774. — The year began with severe frost, and for nearly two months the ground 
was frost-bound ; occasionally there were great rains or snow ; the weather was more 
moderate in April ; the summer was cool with heavy rains. The autumnal months 
were wet, particularly in September. Some snow fell in November and beginning of 
December. This year was remarkably wet. 
1775. — The weather was mild at the beginning of the year. The summer was dry 
MDCCCL. 4 F 
