SEA-FISHERIES LABORATORY. 183 
all. hen the difference between surface and bottom 
oradually decreases until Station IV, which is nearest to 
the Isle of Man, is reached. On the line between Calf 
of Man and Holyhead, the difference is greatest at the 
deep station near the Calf and decreases towards the 
South as the sea bottom rises. This line crosses the 
drifting water passing up the Irish Sea, and it is here, if 
anywhere that indications of a deep current, or stratum of 
different characters from those of the surface, might be 
expected. But the difference is due only to the cooling 
of surface water and the sinking, by convection, of this 
to the bottom. 
All these stations, however, are comparatively 
shallow ones, and it might, perhaps, be expected that 
vertical differences of temperatures would be observed at 
places where the sea is deeper. Nevertheless, the obser- 
vations made by the Irish Department of Agriculture and 
Technical Instruction (which have kindly been communi- 
cated to us by Mr. EK. W. L. Holt) show that the tempera- 
ture differences on the western side of the Irish Sea, and 
over the deep channel between Isle of Man and Ireland are 
sunilar to those found between Isle of Man and Holyhead. 
The results of a special hydrographic cruise made by us 
in this area, and in the deep water off the Galloway coast, 
in June, 1908, are quoted by Dr. Bassett in the preceding 
paper. Two soundings were made on this occasion in the 
deepest part of the sea round the British Isles, 248 to 267 
metres. The temperature™ at a mean depth of 230 
metres was O9(°C., and at the surface 9°82°C., a 
difference of only 0°85°C. Mere the tidal streams are 
very rapid. A sounding taken near the middle of the 
sea-area bounded by the Galloway land, Ireland and the 
* Mean of two soundings made at opposite extremitics of the gutter 
of deep. water. : 
N 
