of the Fishery Board for Scotland. 
361 
Tliis shows that surface and bottom are on the whole equally little affected 
by the tide. When low water occurs in the afternoon, the temperature 
at surface and bottom is 0°'2 higher than in the morning. When high 
water happens in the afternoon, the excess over the morning temperature 
is only 0°*1, showing that, on the whole, the flood tide exercises a cooling 
effect. 
Grouping the daily range of temperature according to tides and the 
season of the year, we find the following results : — 
Surface. 
Bottom. 
Mean Difference. 
High Water 
9 A.M., 
Low Water 
3 P.M. 
Sg - Sg. 
Low Water 
9 A.M., 
High Water 
3 P.M. 
S3 - Sg. 
High Water 
9 A.M., 
Low Water 
3 P.M. 
B3 - B9. 
Low Water 
9 A.M., 
High Water 
3 P.M. 
B3 - B9. 
Warm months, .... 
0-4 
0-1 
0-3 
0-2 
Cold months, .... 
O'O 
0-0 
0-0 
0-1 
That is, that when high water occurs at 9 and low water at 3 in the 
warm months the heating effect of the sun and of the ebb-water from the 
Forth makes the water 0°*4 warmer on the surface and 0°"3 warmer at 
the bottom than at 9 a.m. But in the cold months the cold ebb-water 
from the Forth completely neutralises the feeble heating effect of the sun, 
and no rise of temperature occurs in the afternoon. On the other hand, 
when high water occurs in the afternoon in the warm months and low 
water in the morning the colder water from the North Sea prevents sun- 
heat from raising the surface temperature more than 0°'l in the warm 
months, and allows no rise of temperature at all in the cold months. It 
is probable that the effect is produced by the warming power of the ebb- 
water at 9 A.M. making up for loss by radiation at night, and this would 
completely account for the range being greater at the bottom than on the 
surface, as the surface is naturally more affected by the fresher ebb- water. 
The temperature effect of the Forth is in every way less marked in the 
cold than in the warm months. 
It is unfortunate that the specific gravity observations made at this 
station cannot be utilised. The use of a delicate hydrometer when the 
vessel is rolling heavily is very difficult, and on board the lightships 
accidents frequently happened. The floating thermometer, the readings 
of which are necessary m order to reduce the specific gravity to a standard 
temperature, was unsatisfactory, the column having become broken by 
an air-bubble. 
Bell Bock Lighthouse. — ^The Bell Kock, although entirely covered at 
high water, presents a wide flat surface at low tide, against which the 
waves break heavily when there is any swell or wind. In consequence of 
this it would not be easy to take observations as at the Oxcar Lighthouse, 
where the sea is usually calm ; but a very ingenious plan has been 
adopted to overcome the difficulty. A strong line is carried from the 
gallery at the top of the lighthouse, and made fast to a ring fixed to the 
outer edge of the rock at a distance great enough to make the angle 
comparatively gentle. The thermometer and a bottle weighted with lead, 
in order to sink, and covered with rope- work for protection, are hung from 
a block which runs freely on the fixed line, and can be lowered and raised 
