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mean monthly temperatures for 92 years for Greenwich, have 
been made use of. From ITT 1 to 1849, the observations are 
those supplied by Mr. Glaisher, in the Philosophical Trans- 
actions for 1850. The mean monthly temperatures from 1850 
to 1862, are those given in the Greenwich Observations. 
The difference between the mean temperature of each 
month and the 92 years’ average for the same month was 
found for every month during the year, and the figures were 
collected into two columns according as they were positive or 
negative. The sums of these two columns will he found in 
the table annexed to this Paper, and serve to show the 
number of degrees the mean temperature was above and 
below the average during the year. These figures have been 
laid down in a diagram annexed, and which show the irre- 
gular character, and at the same time proves most distinctly 
that if the mean temperature is above or below the average 
during part of the year, it by no means follows that the 
converse holds good during the remainder of the year. 
During the 92 years, there were 23 in which the total excess 
or deficiency of the mean temperature amounted to over 20°. 
There were 28 in which it amounted to from 10° to 20°; 19 
years in which it amounted to at least 5°, and 22 in which it 
was less than 5°. 
During a very small number of years only is the mean 
temperature, viewed in this manner, at all in a proximate 
state of equilibrium during the year. 
The variations below the average reached their maximum 
value during the period 1781 to 1791, every year but 1781 
being below the average. From 1841 to 1851 there was 
only one year below the average; and from 1851 to 1861, 
only two years below' the average. 
Careful inspection of the annexed diagram at once shows, 
that these variations are exceedingly irregular, and show no 
approach to periodicity of any kind whatever. 
