THE CLYDE SEA-AREA. 



305 



complete observations in the first week of April, 1896, it was not more than 

 1 from 44 0> 8 F. All these represent very nearly the period of annual 

 minimum, and the upper layer of 5 fathoms was at no place more than, and 

 rarelv so much as, 1 warmer than the average of the mass of the water 



* ^^ 



Farh?o 



FIG. 4. 



They amply justify the general statement that at the annual minimum the 

 Clyde Sea-area is homothermic, i.e. is at the same temperature from surface 

 to bottom throughout its whole extent. 



The process of heating up brings into prominence the control that the con- 

 figuration of the various divisions exercises on the march of temperature in 

 the water, the greater the restriction of communication with the open sea 

 the slower being the propagation of warmth downward, and the longer the 

 period after the surface has begun to cool again before the seasonal 

 maximum reaches the bottom. This is very clearly shown in the curves. 



Taken as a whole the observations of 1886-88 showed that while the mean 

 annual temperature of the air was 47, the mean annual temperature of the 

 upper 5 fathoms of water was 48'8, showing that the inflowing ocean water 

 is on the average of the year warmth-bringing. For about 240 days the 

 surface-water was warmer than the air, and the air was warmer than the 

 surface- water for only 125 days in the year, i.e. for eight months out of the 

 twelve the" air is being warmed by the water. As 1887 was a typical year 

 and the various temperature trips were happily timed to catch the critical 

 points in the curve of seasonal change the table on page 396 gives a fair idea 

 of normal temperature changes. 



The retardation of phase and restriction of range in deep water by isolation 

 from the open sea is illustrated by the following table of temperatures at a 

 depth of 40 fathoms for various seasons in the year 1886 which started from 

 the lowest minimum observed in the course of these researches. 



TABLE IV. COMPARISON OF TEMPERATURE AT 40 FATHOMS. 



