CLYDE SEA AREA. 131 



for tlie year, 49°'4. Outside, the surface had cooled 11°"5, and the bottom 3°7, since No. 

 XII. ; inside, the surface had cooled 9°1, and the bottom had warmed 2°. The maximum 

 temperature inside was 50° at 20 fathoms, half a degree warmer than the bottom, and 

 4° '8 warmer than the surface. 



Section XIV., Februa/ry 9th-l0th, 1888. — Four stations were examined. The 

 upper layers were distinctly warmer than in No. XIII., but the bottom was 4° '3 colder 

 outside and 3° "2 colder inside than on the former occasion. Below the level of the bar 

 the water outside was homothermic at 45°, that inside at 46°. The isotherms showed 

 a strong seaward slope, indicating a mixture and out-flow of the surface water. Ebb 

 tide preponderated, and the wind was W.N.W., or in the main down-loch, and squally. 

 This section may be profitably compared with No. XII. for the relation of dip of 

 isotherms to wind. 



Section XV., March 1st, 1888. — Three stations only were studied. The temperature 

 varied only from 44° '0 to 44° *9 inside, so that no evidence as to circulation was afforded. 

 The surface (whole depth outside) had cooled down 0°7 ; the bottom inside had cooled 

 2°. This very rapid cooling of the bottom layers, and the general equalisation of 

 temperature throughout the basin, is characteristic of the spring minimum, but was more 

 marked in 1888 than in 1887. 



Section XVI., March 28th, 1888. — Three stations were again visited. Slight general 

 cooling had occurred. Outside, the surface temperature was 43° (the same as in No. 

 XV.), the bottom 42°*6, or 0°*7 colder. Inside, the surface temperature was 43 0- 3, the 

 bottom 43°*1, the maximum, a little under 44°, occurring at 10 fathoms. No evidence 

 as to circulation appeared. 



Section XVII, September 3rd, 1888. — This was the last trip, and included three 

 stations. The general distribution of temperature in its main features resembled that 

 of the two previous Septembers, only outside the bar the surface was warmer and 

 the bottom water colder than in former cases. The isotherms were appreciably 

 horizontal. The fall of temperature from 56° on the surface to 51° at the level of the 

 sill was uniform over all. Outside, the further fall to 48° '2 on the bottom was very 

 gradual ; while inside, the fall to a little under 44° was rapid and almost perfectly 

 uniform. The minimum occurred at 35 fathoms, the bottom being a fraction of a degree 

 warmer. As in both the previous Septembers, the bottom temperature inside was 4° 

 lower than that outside. 



From reasoning based on the great rainfall of the Loch Groil catchment basin, and 

 the relatively high and constant salinity of the water in the loch, it is plain that there 

 must be a double circulation always in operation, the flowing out of fresher and the 

 flowing in of Salter water. It is surprising that the isotherms show so little evidence of 

 this circulation, especially as the contrast of temperature on the two sides of the bar is 

 usually sharp. The only way of explaining this is that the circulation must be mainly 

 effected by the tides, working continuously but so gradually that the small quantity of 

 salt water brought in accommodates its temperature to that of the mass of the water in 



