426 
Proceedings of the Royal Society 
Further, the rate of loss of heat, due to radiation alone, must he 
very much greater during a winter night than during a summer one. 
The rise of temperature in the bottom water and deeper layers is 
made more apparent by considering the actual readings of the 
thermometer employed as given by the millimetre scale on the stem. 
Depth, 
65 fathoms. 
85 fathoms. 
100 fathoms. 
No. of thermometer, 
9 
80 
21 
Date. 
S-H 
Read- 
Difference. 
Read- 
Difference. 
Read- 
Difference. 
Cl) 
-1-3 
P 
ing. 
ing. 
ing. 
days 
mm. 
mm. 
F. 
mm. 
mm. 
°F. 
mm. 
mm. 
° F. 
September 5, . 
51-0 
70-1 
60*5 
September 22, . 
17 
51-6 
*0-6 
0*17 
70-4 
6-3 
o' : io 
60-4 
-o-i 
-0**03 
October 15, 
23 
52-4 
0-8 
0-23 
71-0 
0-6 
0-21 
60-9 
+ 0-5 
+ 0-16 
November 14, . 
30 
52-2 
-0-2 
-0-06 
71-2 
0-2 
0-07 
61-2 
0-3 
0-09 
The position of the index in the thermometers when referred to 
this scale can be fixed almost to one-tenth of a millimetre, certainly 
to one-fifth. In thermometer Ho. 9, 1 millimetre = 0 o, 285 F. ; in 
No. 80, 1 millimetre = 0 o, 3 45 F. ; and in No. 21, 1 millimetre = 
0°*31 F. The difference of 0T millimetre between the readings 
of No. 21 on 5th and on 22nd September cannot be depended on 
as real. It is probable that between these dates and during the 
whole of the summer the temperature had been quite constant. 
Between 22nd September and 14th November the whole rise of 
temperature at the bottom is only 0 o- 25, and it may be confidently 
affirmed that at a depth of 100 fathoms the whole range of 
temperature during a single season does not exceed 0 o, 3 F. By 
season is meant the summer and winter half of the year, or the 
period between the date when heating begins in the spring, and that 
at which the summer heat has been almost wholly lost, and when 
the water begins again to assume a sensibly uniform temperature 
from top to bottom. At 85 fathoms the temperature had begun 
distinctly to rise on 5th September, and by 14th November it had 
evidently reached about its maximum. At this depth, therefore, 
the summer range is at least 0°*4 F. At 65 fathoms the water 
had begun to cool between 16th October and 14th November. In 
order to determine the range at this depth, it will be necessary to 
have observations earlier than 5th September. 
