576 MR. GLAISHER ON THE THERMOMETRICAL OBSERVATIONS TAKEN AT 
Determination of the Monthly Mean Temperature of the water of the Thames hy night 
and hy day, from the year 1846 to the year 1849. 
The observations to determine the temperature of the Thames water are made by 
Lieut. Sanders, R.N. The instruments consist of one maximum thermometer and of 
one minimum thermometer, suspended from the sides of the Dreadnought Hospital 
Ship, in a perforated trunk placed at about 2 feet below the surface of the water. The 
range of temperature during the day is usually about 2°, and the simple arithmetic 
mean of the readings of the maximum and minimum thermometers shows the mean 
temperature of the water. 
Table XIO. — Mean monthly temperature of tlie water of the Thames. 
1 Month. 
1846. 
1847. 
1848. 
1849. 
Mean of all the 
readings in each 
month. 
Mean 
tempera- 
ture of 
the 
water. 
Mean of all the 
readings in each 
month. 
Mean 
tempera- 
ture of 
the 
water. 
Mean of all the 
readings in each 
month. 
Mean 
tempera- 
ture of 
the 
water. 
Mean of aU the 
readings in each 
month. 
Mean 
tempera- 
ture of 
the 
water. 
Max. 
Min. 
Max. 
Min. 
Max. 
Min. 
Max. 
Min. 
1 January.... 
44-3 
42-0 
43-2 
3^1 
3^5 
36-3 
' 35-7 
35-1 
35-4 
41-6 
39-6 
40-6 
1 February... 
45-3 
42*5 
43-9 
38-9 
37-2 
38-1 
41-8 
40-3 
4M 
44-2 
42-6 
43-4 
1 March 
48-2 
46-3 
47-3 
42-1 
41-4 
41-8 
45-7 
44-1 
44-9 
1 April 
51-5 
49-4 
50*5 
46*9 
46-4 
46*7 
51-1 
50-2 
50“6 
47-9 
44-8 
46-3 
1 May 
59-9 
57-2 
58-6 
58-6 
57*0 
57*8 
' 62'5 
61-0 
61-8 
i 58-9 
55-7 
57-3 
73-0 
70*8 
71-9 
65-5 
61-9 
63-7 
63’6 
62'6 
63-1 
j 65-2 
63-3 
64-3 
July 
67-4 
66-1 
66-7 
70*6 
66*5 
68-6 
66-0 
65-0 
65*5 
67-8 
66-1 
67-0 
August ... 
68-3 
66-7 
67-5 
66-1 
64-4 
65-3 
, 63-0 
()2-0 
62-5 
64-9 
62-7 
63-8 
September. 
64-7 
63'5 
64-1 
57-0 
56-5 
56-8 
: 59-5 
58-8 
59”1 
61-4 
58-7 
60-0 
October ... 
54-2 
52-8 
53-5 
53*3 
53*0 
53-a 
53-7 
50-8 
52-2 
52-8 
49-5 
51-2 
November. 
i 47-6 
46-0 
46-8 
47-9 
47-3 
47*6 
j 
47-1 
44-1 
45-6 
December. 
37-6 
34-9 
36-3 
42*5 
41-5 
42-0 
i 43-9 
40-5 
42'2 
40*3 
36-8 
38-6 
By comparing the means of these numbers for the four years, with the means of 
the readings of the maximum and minimum thermometers in air at the Royal Ob- 
servatory, for the same months, we find that the mean lowest readings of the water 
were higher in the twelve months respectively by 3°‘9 ; 4°'6 ; 7°'/ ; 12°‘3 ; 1 1°‘5 ; 16°7; 
12°'4 ; 10°’4 ; 10°‘7 ; 6°'8 ; 6°'3 and 4°-9, than the mean of the lowest readings of the 
air ; and it was lower than the mean m.aximum readings of the air by 3°‘2 ; 4°‘6 ; .5°'3 ; 
9°'2 ; 6°‘0 ; 7°'5 ; 8°‘l ; 6°‘7 ; 7°’4 ; 6°'0 ; 4°'7 and 3°*0, in the respective months from 
January. These numbers are very large, and will fully account for the little higher 
temperature possessed by places in the vicinity of the river, and these differences of 
temperature are probably the fruitful source of the London fogs. 
Mr. Sanders, at my request, has taken daily observations of tlie temperature of the 
air at 32 feet above the water of the Thames at the hours of 6 a.m. and 6 p.m. during 
the years 1847 and 1848, and at the hours of 9 a.m. and 9 p.m. in the year 1849. 
The result of these observations, compared with simultaneous observations taken at 
the Royal Observatory, is as follows : — that the temperature of the air 32 feet above 
