364 
Part III. — Ninth Annual Eeport 
In order to compare the relation of bottom and surface temperature 
at different seasons, the tables enable us to draw up the following 
statement : — Cold Months. Warm Months. 
9 a.m. 3 p.m. 9 a.m. 3 p.m. 
Surface, .... 5*9 6'1 11-5 11-7 
Bottom, .... 6 0 6-1 11 '3 11 '5 
Difference, S—B, . . -O'l O'O 0*2 0-2 
The range between surface and bottom is too small to make it 
necessary to discuss the intermediate temperatures. 
Thus, in the warm months, the surface water remains 0°-2 warmer 
than the bottom on the average, and the whole mass of water is 
uniformly warmed by 0°"2 between 9 a.m. and 3 p.m. This is a much 
less range for depth than at the Carr Rock, as may be understood 
from the shallower water, and it is also a much less range from morning 
to afternoon, a fact which does not admit of such ready explanation. 
In the cold months, the surface averages 0°'l lower than the bottom 
in the morning, but, heating more rapidly, the temperature is equalised 
by the afternoon. 
The strong tidal effects at such a place necessarily produce changes 
of temperature, which to a large extent neutralise each other in the 
mean of many observations. The observations were accordingly classified, 
as in other cases, into two groups, one including all those which were 
taken within about two hours of high water at 9 a.m., and low water 
at 3 P.M. ; the other including those taken within about two hours 
of low water at 9 a.m., and high water at 3 p.m. Each group comprised, 
as a rule, three days in a fortnight, or six days in the month, so 
that about half the observations were available for use in the discussion. 
The results are expressed as follows in a compressed summary : — 
Abertay Light-vessel — Mean Tidal Effect on Temperature. 
Surface. 
Bottom. 
Month. 
High 
Low 
Low 
High 
High 
Low 
Low 
High 
Water [Water 
9 a.m. 3 p.m. 
S3-S9 
Water 
9 A.M. 
Water 
3 P.M. 
S3-S9 
Water 
9 A.M. 
Water 
3 P.M 
B3-BJ 
Water 
9 A.M 
Water 
3 P.M. 
B3-B9 
S9. 
S3. 
S9. 
S3. 
B9. 
B3. 
B9. 
B3. 
1889. 
June. 
10-0 
12-5 
2 '5 
12-4 
10-5 
-i'9 
9-3 
11-4 
2'I 
11-7 
10-0 
-17 
July. 
12-0 
13-1 
I'l 
1 13'1 
12-6 
11-8 
12-9 
I'l 
13-1 
12-6 
-o'5 
Aug. 
13-3 
13-9 
o'6 
13 '7 
13'4 
-03 
13-4 
13-6 
0"2 
13-5 
13-3 
-0'2 
Sept. 
13-0 
13-3 
o'3 
12 '7 
12-7 
O'O 
13-1 
13'1 
O'O 
12'7 
12 '7 
O'O 
Oct. 
10-7 
10-7 
O'O 
9-7 
10-5 
o'B 
11-1 
10-8 
-O'S 
9-7 
10-6 
o'9 
Nov. 
9-5 
8-7 
-0-8 
9-3 
9-6 
o'3 
9-7 
9-3 
-o'4 
8-8 
9 '7 
o'9 
Dec. 
7-0 
6-2 
-0-8 
5-5 
7-3 
T-8 
7-4 
6-5 
-o'9 
6-2 
7-5 
I '3 
1890. 
Jan. 
5-6 
5-1 
-o'S 
5-5 
6 1 
o'6 
6 '4 
6-0 
-o'4 
5-8 
6-4 
o'6 
Feb. 
5-0 
4-6 
-0-4 
5-1 
6-0 
o'9 
5-2 
5-0 
-0'2 
5-6 
6-1 
0-5 
Mar. 
5-6 
6-4 
0-8 
4-9 
5'1 
0'2 
5 '6 
5-8 
0'2 
5'1 
5-3 
0'2 
April. 
6-4 
6-8 
0-4 
6-6 
6-1 
-O'S 
6 '4 
6-6 
0'2 
6-8 
6-2 
-0-6 
May. 
8-6 
10-0 
I '4 
9-1 
8'1 
- I'O 
8 '6 
9 '5 
o'9 
9-0 
8-0 
- I'O 
June. 
10-1 
121 
2'0 
11-2 
9-5 
-17 
9-8 
10-5 
07 
ll'O 
9 '5 
-0-5 
July. 
11-2 
12-9 
17 
12'7 
11-4 
-i'3 
11-3 
12-3 
I'O 
12-4 
11-2 
- I'2 
Aug. 
12-1 
13-6 
I '5 
13 '3 
12-2 
- I'l 
12'5 
13 '2 
07 
13-2 
12-2 
-I'O 
Sept. 
12-6 
13-3 
07 
13-3 
12-7 
-0-6 
12-7 
13-1 
0-4 
131 
130 
-O'l 
Oct. 
11-3 
110 
-0-3 
. lO'l 
10-8 
07 
11-5 
11'4 
-O'l 
10-4 
11-0 
o'6 
Nov. 
8-9 
8-2 
-07 
6-7 
8-8 
2'I 
9-6 
9-2 
-o'4 
7'5 
9-1 
1-6 
Dec. 
6-9 
5-8 
- I'l 
5 '2 
6'7 
7'5 
6'7 
-o'8 
5-4 
7-1 
17 
1891. 
Jan. 
5-2 
3-8 
-i'4 
3 '4 
3-8 
o'4l 
5-3 
4-6 
-o'7 
4-7 
4-8 
o'l 
Feb. 
5-1 
4-9 
— 0'2 
4 '8 
5-3 
0-5 
5-1 
5-1 
O'O 
4-9 
5 '3 
o'4 
March. 
4-9 
4-7 
-0'2 
3-8 
4-4 
o'6 
50 
4-9 
-OI 
3-9 
4-5 
o'6 
Mean, 
8-9 
9-2 
o*3 
8-8 
8-9 
01 
9-0 
9'1 
O'l 
8-8 
8'9 
O'l 
Mean, 
(disregarding 
sign). 
o'9 
o'9 
O'S 
07 
