CLYDE SEA AREA. 



121 



1886-88, the average period of air warmer than water was for the divisions Channel, 

 Arran Basin, Loch Fyne, and Gareloch, 134, 136, 143, and 124 days ; while for air colder 

 than water the figures were 237, 223, 219, and 248 days. The rapid heating of the 

 Gareloch by radiation brings up the water-temperature so near the air-temperature that 

 a short time of air-cooling equalises the two, and stops further heating in the water. 



Interpolating, as in previous cases, probable values for the first three months of 1886 

 and the last three of 1888, we get from fig. 47 the data for comparing the mean annual 

 temperature of water and air. 



Table XLVI. — Mean Annual Temperature of Air and Water for the Gareloch. 



Year. 



1886 

 1887 

 1888 

 Mean 



I. Air (Mean 

 for Area). 



46°-2 

 47°-0 

 46°-7 

 46°-63 



II. Air 



(Helensburgh). 



46°-5 

 45°-9 

 47°-3 

 46°-57 



III. Water 

 (Mass). 



47°-4 

 48°-7 

 47-5 

 47°-87 



IV. Water 

 (0-5 Fathoms). 



47°-5 



48°-7 

 47°-6 

 47°-93 



Difference 

 (Air II. and 

 Water III.). 



Difference 

 (Air I. and 

 Water III.). 



-° '9 



-2°"8 



- 0°'2 



- i°'3o 



- I - 2 



-i°7 

 -o°-8 



- i°'23 



The mean temperature of the air at Helensburgh for 1887 is doubtful, as three 

 months had to be interpolated. The early spring of that year was exceptionally cold at 

 Helensburgh compared with the other Clyde stations, hence the low annual average. 

 The mean, as calculated for the difference between the water and local air, or general 

 air-temperature, is practically the same, so that one has some confidence in saying that 

 the mass of water in the Gareloch (which is practically at the same temperature as the 

 superficial layer) is a degree and a quarter warmer than the air, a somewhat greater 

 excess than in the case of the surface water of Loch Fyne. Taking the average of the 

 years 1886 and 1887, so as to be comparable throughout, the surface 5 fathoms of water 

 in the various divisions were warmer than the air to the following amounts :— Channel, 

 1°7 ; Arran Basin, 1°7; Loch Fyne, 1 0> 5 ; Gareloch, 1°'9 (or, taking general air- 

 temperature, 1 0, 5). The variation is so slight as to be negligable, and we are justified 

 in saying that for these two years the surface layer of 5 fathoms of water in the Clyde 

 Sea Area was 1 0, 6 warmer than the overlying air. Considering the mass of water, and 

 not the surface layer, we find the Channel and Gareloch practically the same, an excess 

 of 1°7, while the excess of the Arran Basin is only 0°'35, and of Loch Fyne 0°-45. 



Loch Goil. 



The physical features of Loch Goil are described in Part L, p. 647. The name is 

 applied to the water surface lying within a bar rising to 7 fathoms, which marks off Loch 



VOL. XXXVIII. PART I. (NO. 1). q 



