228 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



isotherms the temperatures for the mean dates in question 

 have generally been obtained from them. 



Temperature Stratification. 



There are no reasons for modification of the statement 

 made in last year's Report that the Irish Sea is a 

 practically homothermic water mass, showing no 

 significant variation of temperature with depth. The 

 data relating to the hydrographic soundings are tabulated 

 in Dr. Bassett's Report, and it will be seen that the 

 variations of temperature with depth of water are small 

 and inconstant. Such as they are, they appear to me to 

 depend entirely on (1) convection currents set up by the 

 chilling of the surface waters, and (2) lateral shore drifts 

 set up by winds, and by the relative differences in 

 temperature near and remote from the shore. It has been 

 pointed out that as the coastal water heats up in summer 

 at a greater rate than the off-shore water, it must tend to 

 stand at a higher level, and thus oif-shore currents or 

 drifts must be set up at the surface, while deep currents 

 set in towards the land to restore equilibrium. Obviously 

 these off- and on-shore drifts will be partially, or perhaps 

 entirely masked by the influence of the tidal streams. 

 Further, there is the strong effect of the latter in 

 conveying masses of heated or chilled water to and from 

 the shore. The Irish Sea and St. George's Channel are a 

 relatively shallow water area, and the northerly drift 

 through this is too weak to set up notable temperature or 

 salinity, stratification. We find, then, that at stations 5, 6 

 and T the differences in temperature between surface and 

 bottom water never amounted to more than 0'7° C, and 

 were usually much less. The greatest differences detected 

 were at stations 1 to 4 during the June cruise, during and 

 after a spell of fine weather, when the bottom water was 



