360 
Part III. — Ninth Annual Report 
0°"2 at 9 A.M. and 0°*1 at 3 p.m., the surface being in each case the 
warmer. Taking the monthly means, however, and grouping them into 
cold months (December-April and December- March), and warm 
months (May-November), the following results appear : — 
Cold Months. Warm Months. 
9 A.M. 3 P.M. 9 A.M. 3 P.M. 
Surface temperature, . . 5-9 61 10-9 11-2 
Bottom . . 61 «-2 10-4 10-6 
Difference, . . . -0*2 -01 O'S 0-6 
Putting these figures into words. During the cold months of the year 
the surface water is from 0°-l to 0°-2 colder than the bottom, and during 
the warm months of the year the surface is rather more than half a degree 
warmer than the bottom. It is not impossible that such a difference of 
temperature may influence the depth at which various species of micro- 
scopic pelagic fauna are to be found at different seasons, the presumption 
being that in winter they would seek deeper water on account of its higher 
temperature. In December 1889 the bottom water averaged 0°*7 warmer 
than the surface; or, expressing the difference in the Fahrenheit scale, 
1°*3 — a difference which might well affect small organisms. 
The effect of tide on the variation of temperature at the Carr Rock is 
one of some interest, as the flood tide sweeping from the north might be 
expected to carry the fresher surface water of the Tay past the ship, rais- 
ing the temperature in summer and lowering it in winter, while the Salter 
and colder sea water of the North Sea would simultaneously affect the 
bottom water. The ebb tide, on the other hand, would carry the Firth of 
Forth water of nearly uniform salinity and temperature past the ship. In 
winter this should very slightly lower the surface temperature and still 
more slightly raise that at the bottom. In summer the reverse effect 
would be anticipated. The entire series of observations was sifted out and 
rearranged according to tidal phase, as in the case of Oxcar ; in the 
following table high water and low water include observations made within 
one and a half hours of each event. 
NoKTH Carr Light-vessel — Mean Tidal Effect on Temperature. 
Surface. 
Bottom. 
Month. 
High 
Water 
9 a.m. 
Low 
Water 
3 P.M. 
S3. 
S3-S9. 
Low 
Water 
9 A.M. 
S9. • 
High 
Water 
3 P.M. 
S3. 
S3- Sg. 
High 
Water 
9 A.M. 
B9. 
Low 
Water 
3 P.M. 
B3. 
B3-B9. 
Low 
Water 
9 a.m. 
B9. 
High 
Water 
3 P.M. 
B . 
B3-B9. 
1889. , 
Dec. ' 
1890. 
Jan. 
Feb. • 
March. 
April. ; 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
1891. 
Jan. 
Feb. ; 
March. 
71 
6-2 
5- 4 
57 
6- 5 
9-7 
10- 6 
11- 7 
11-7 
13-0 
11-3 
9-0 
7- 4 
5-6 
5-4 
51 
7-0 
6-2 
5-4 
5- 7 
6- 8 
9-9 
10- 5 
12-4 
12- 8 
13- 3 
11- 5 
9-3 
7- 3 
5-3 
5-4 
5-2 
-O'l 
o*o 
o'o 
O'O 
o'3 
0'2 
— O'l 
07 
II 
o"3 
0"2 
03 
-O'l 
-0'2 
00 
O'l 
6 '6 
6-5 
5'6 
6'4 
6 '2 
7'9 
10- 6 
11- 5 
12- 0 
12-6 
111 
8-9 
71 
6-2 
5-3 
4 '7 
6 '7 
6-7 
5-6 
5- 4 
6 '5 
8-3 
10-0 
12'1 
12-3 
12-9 
111 
8-7 
6- 5 
5-3 
5-4 
4 '8 
O'l 
0'2 
O'O 
O'O 
o'S 
o'4 
-o'6 
o'6 
0-3 
o'3 
O'O 
-0'2 
-o'6 
o'l 
O'l 
O'l 
7 '9 
6- 4 
5'6 
5 '3 
6 '4 
7- 8 
9-4 
10 '5 
11'7 
126 
11-6 
9-5 
8- 0 
5'3 
5-4 
5-2 
7 '9 
6-2 
6- 8 
5-4 
6 '3 
8'0 
9-2 
11-4 
12 '3 
13 '0 
11-7 
9 '7 
7- 7 
5 '5 
5'6 
5-2 
O'O 
-0"2 
0*2 
O'l 
-O'l 
0'2 
-0'2 
o'9 
o'6 
o'4 
O'l 
0'2 
-o'3 
0'2 
0'2 
00 
6-0 
6- 9 
61 
5-2 
61 
7 '4 
9'0 
10- 7 
11- 8 
12- 4 
11-4 
8 '7 
7- 4 
51 
5 '6 
4'7 
6- 5 
6'9 
61 
5 '2 
61 
7 '6 
91 
111 
11-9 
13'0 
11'3 
9-0 
7- 3 
5-6 
5 '6 
4-8 
O'O 
O'O 
00 
O'O 
0'2 
O'l 
o'4 
O'l 
o'6 
-O'l 
o*3 
-O'l 
O'S 
O'O 
O'l 
Mean, 
8-2 
8-4 
0'2 
7-9. 
8'0> 
O'l 
8'0 . 
8'2. 
0'2 
7'8 
7-9 
O'l 
