THE ROYAL SOCIETY, AND AT THE ROYAL OBSERVATORY, GREENWICH. 583 
The mean of all the differences between the hottest and coldest months in every 
year is 28°’5. 
In the year 1/90 the difference was 21°-3 only, and in the year 1780 it was as large 
as Sf'^'l, these numbers being respectively the smallest and largest within the period 
of seventy-nine years. 
The coldest month in the year has occurred in January forty- three times, in February 
fifteen, in December twenty-one, and in March once ; this unusual circumstance took 
place in the year 1837. 
The hottest month in the year has taken place five times in June, forty-seven times 
in July, twenty-five times in August, and three times in September. 
The following are the values of the extreme mean temperatures in every month ; — 
In January 
In February 
In March 
In April 
In May 
In June 
In July 
In August 
In September 
In October 
In November 
In December 
1795 the mean temperature was 23'9, and 
1785 the mean temperature was 30'4, and 
1785 the mean temperature was 33'9, and 
1771 the mean temperature was 38' 7, and 
1773 the mean temperature was 47’5, and 
1816 the mean temperature was 53T, and 
1816 the mean temperature was 54'5, and 
1817 the mean temperature was 55’4, and 
1786 the mean temperature was 51 '3, and 
1784 the mean temperature was 43' 9, and 
1782 the mean temperature was 34’7, and 
1788 the mean temperature was 29‘0, and 
in January 
in February 
in March 
in April 
in May 
in June 
in July 
in August 
in September 
in October 1811 
in November 
in December 
1796 
1794 
1780 
1844 
1848 
1846 
1778 
1780 
1815 
and 1831 
1822 
1806 
it was 45’3. 
it was 44-7. 
it was 49’2. 
it was 51'7. 
it was 59'7. 
it was 65‘3. 
it was 67 ' 0 . 
it was 65 ■7. 
it was 62‘3. 
it was 55'0. 
it was 48' 2. 
it was 46'8. 
It is clear from these numbers that observations for a few years only can never be 
of great importance, when we consider that the difference of the monthly means of 
the winter months may be as large as 20°, and of the summer months of 1 1° or 12°. 
By taking the means of the numbers in the Table in different groups of years the 
next Table is formed. 
Table XIX. — Showing the mean temperature of the Air at the Royal Observatory, 
Greenwich, in every month in successive groups of years. 
Period. 
Jan. 
Feb. 
March. 
April. 
May. 
June. 
July. 
August. 
Sept. 
Oct. 
Nov. 
Dec. 
From 1771 to 1779. 
33-5 
3^7 
41-6 
45-6 
52-0 
58-4 
62-0 
61-2 
55-6 
49*5 
41-8 
39-4 
From 1780 to 1789. 
34-9 
36-6 
38-8 
44-9 
52-8 
58-4 
61-5 
60-0 
55-7 
47-3 
40-5 
36-1 
From 1790 to 1799. 
35-8 
38-5 
40-4 
45*9 
50*9 
56-3 
60-9 
60-1 
55-8 
48-9 
41-8 
37-5 j 
From 1800 to 1809. 
37-0 
38-5 
40-6 
45-1 
53-7 
57-6 
61-3 
62-1 
56-6 
49-6 
41-8 
39-1 
From 1810 tol819. 
35-2 
39-2 
41-3 
45-6 
51*6 
56-8 
59-9 
59-4 
57*8 
49-9 
42-4 
37-8 
From 1820 to 1829. 
35-4 
38-1 
41-8 
46*8 
52-6 
58-2 
61-8 
60-2 
56-7 
49-9 
43-3 
40-8 
From 1830 to 1839. 
36-0 
38-5 
41-3 
44-5 
52-9 
58*8 
62*3 
60-3 
55-4 
50-1 
43-1 
39-9 
From 1840 to 1849. 
37*6 
38-4 
41-9 
46-9 
54-3 
59-6 
61-2 
61-2 
56-8 
49-5 
44-0 
39-7 
The next Table is formed by taking the difference between the mean temperature 
of each month, as found from all the years, and the mean temperature of the same 
month in every year. 
