CLYDE SEA ABEA. 31 



expected, highest in the open basins and lowest in the enclosed lochs. No observations 

 were made on the Great Plateau or in the Channel. The arrangement of temperature 

 in all the parts examined was similar to that of the two previous Augusts. 



Trip XXIII., October 1888. — Observations were taken in the landward part of 

 the Area, from October 16th to 25th, in calm weather, and these admit of comparison 

 with observations made on the West Coast of Scotland, further north, on the 5th and 

 6th. August and September had been slightly below the average with regard to air- 

 temperature, but October was a normal month. 



The water-temperatures observed showed that surface- cooling had set in. This did 

 not always show itself by the surface layer being colder than that immediately below, 

 but rather by the formation of a homothermic body of water at about 50°, 15 fathoms or 

 more in thickness, beneath which there was a steady fall of temperature to 44° '2 in Loch 

 Fyne, 45°'0 in Loch Goil, and 48°'6 in the deepest part of the Arran Basin. The 

 Dunoon Basin, Loch Strivan, and the Gareloch were entirely occupied by the warm 

 surface stratum, which reached the depth of over 50 fathoms in some places. 



A sounding of 73 fathoms in the Sound of Jura on October 1st, and another of 45 

 fathoms in the Firth of Lome on the 9th, showed that 53°*5 was the uniform temperature 

 from surface to bottom of the margin of the ocean. In Loch Aber a temperature of 53° 

 prevailed to the bottom, and Loch Etive was also much warmer than the lochs of the 

 Clyde Sea Area. 



General Results of the Trips. — It was by an accident of a very remarkable kind 

 that the thermal condition of the water on Trip I. should be so uniform, both in super- 

 ficial, and vertical distribution as to arouse no suspicion whatever of the true 

 determining causes of temperature change. On every other occasion during the three 

 and a half years covered by the observations, the importance of the physical configura- 

 tion of the Area was strongly, or at least clearly, marked. Broad distinctions were 

 indicated between the different natural divisions of the Area which, while originally 

 marked off with regard to configuration alone, were found to have a distinct thermal 

 individuality. Arranged according to iD creasing restriction in communication with the 

 ocean, these divisions are the Channel, Great Plateau, Arran Basin, Dunoon Basin, Loch 

 Strivan, the mountain lochs (Loch Fyne and Loch Goil). The Gareloch occupied a 

 place by itself, or rather along with the Estuary, as showing the influence of the land 

 in an exaggerated manner. Speaking generally, the more completely isolated each 

 natural division was, the more slowly were thermal changes carried on as the seasons 

 succeeded each other, and the lower was the mean annual temperature. 



Thermal Conditions of the Divisions of the Clyde Sea Area. 



The remainder of this memoir is occupied with a discussion of the conditions of each 

 of the natural divisions carried as far as seemed reasonable in each case, and finally 

 by a general statistical summary of the whole work. 



