SEA-FISHERIES LABORATORY. 181 
offshore is much warmer than the water inshore, so that 
the 7°-8° isotherm occupies roughly the same position in 
February as the 14°-15° line does in the summer. In 
August the 16° isotherm runs close to, and parallel with, 
the English coast; while in February the 3°-4° line 
occupies much the same position. 
The cause of this peculiar distribution of tempera- 
ture is the direction of the tidal streams in the eastern 
part of the Irish Sea. The South tidal wave runs up 
St. George's Channel and bending round Anglesey, 
according to “Ferrel’s Law,” turns to the East into 
Liverpool Bay. The North tidal wave sweeps down the 
North Channel and splits on Point of Ayre, and the major 
portion of the stream runs between Isle of Man and 
Cumberland; a much less rapid tide runs along the West 
side of the Isle of Man, the North and South streams 
meeting about Contrary Head, while out between the 
Calf and Loch Carlingford in Ireland, the streams are 
hardly perceptible. On the English side the two tidal 
streams interfere between Morecambe Bay and Maughold 
Head, in the Isle of Man. ‘Therefore, the whole sea area 
between the coast of North Lancashire and the Isle of 
Man is affected by the tidal water surging into and out 
from Morecambe Bay. It is heated in the summer and 
cooled in the winter, by the powerful influence of the 
latter extensive tract of shallow water. 
The Vertical Distribution of Temperature. 
The data for the study of the vertical distribution of 
temperature are included in the tables contained in the 
reports by Dr. Bassett,* on the hydrographic observa- 
tions. The temperatures recorded as the results of well 
* Annual Report Lancashire Sea Fisheries Laboratory, for 1907, 
Liverpool, 1908, pp. 54-79; and pp. 44-64 of the present Report. 
