SEA-FISHERIES LABORATORY. 179 
the alternating masses of colder or warmer water would 
be carried to a varying distance from the land. I think ~ 
that the curves in figs. 11 and 12 show this effect of the 
tides very clearly. The dotted line represents the height 
of the tide at Liverpool from day to day—it indicates 
springs and neaps. Now, in these the fortnightly 
periodicity of temperature change in the sea-water is very 
plainly seen. For about a week, speaking roughly, the 
temperature of the sea at Morecambe Bay Light Ship 
falls below the mean, and during the succeeding week it 
rises above the mean. ‘That is, the smaller temperature 
variations are to be associated with the fortnightly rise 
and fall in the height of the tides. Of course, the corre- 
spondence of the two series of changes is not very exact: 
one can hardly expect it to be since the surface drift of 
water due to high winds must have a certain influence, 
and the phases of the curves do not always coincide. But 
I think it is clear that the main cause of the smaller tem- 
perature variations in the sea off the West Coast of 
England is the transport of water masses of different 
temperature by the tidal streams. 
This conclusion is supported by the study of the 
isotherms in the Irish Sea. At the present time we do 
not possess sufficient data to enable these to be drawn for 
different periods of the year, and I only give one chart, 
fie. 15, which shows the positions of these lines for the 
beginning of August, 1908—the local period of maximum 
temperature of the sea. It will be seen that they do not 
run parallel to the coast as might at first be expected, but 
rather roughly parallel to the twenty-fathom contour-line 
of sea depth. Outside this contour-line the water is 
influenced to a much less extent by the land, than within 
it. The 14° isothermal-line curves round East from the 
Skerries at Holyhead parallel to the coast of Anglesey, 
