CLYDE SEA AREA. 85 



temperature (i.e. 228 clays of heating) to 46 o, ; and only 53 clays were necessary to 

 carry it back to 45°'2. In 1887, starting from 44°*7 in May, 221 clays brought the 

 bottom temperature to 46° "2, and 101 days more brought it back to 43° "8. 



Thus the rise of temperature at the bottom was at the average rate of o, 008 per clay 

 in 1886 and 0°'007 in 1887 ; while the fall of temperature took place at the average rate 

 of o- 015 per day in 1886 and o, 023 in 1887. The average rate of cooling at the 

 bottom for the two years under consideration appears to be two and a half times as 

 rapid as the average rate of heating ; in other words, the heat gained in five days is lost 

 in two. 



The seasonal changes of temperature at Strachur are represented diagrammatically by 

 the time-depth figure (fig. 8, Plate V.), which is on the same scale as that for Skate Island, 

 with which it may profitably be compared. 



The most striking contrast between the two is the strongly-marked diagonal run of 

 the isotherms in the Strachur diagram, and the fact that the penetration of heat was 

 oreatest in 1887, while for Skate Island it was greatest in 1886. The retardation of the 

 date of maximum temperature as the depth increases is beautifully brought out. 



In 1886 the surface was above 50° from July 1st to October 15th, and the isotherm 

 of 50° only reached its maximum depth (23 fathoms) on October 1st. It thus took 92 

 clays to carry this isotherm 23 fathoms clown, while at Skate Island 110 clays sufficed to 

 carry it to 105 fathoms. 



In 1887 the surface was above 50° from May 24th to November 1st, and the 

 temperature of 50° penetrated to its greatest depth (30 fathoms) on September 24th, 

 thus requiring 123 clays to work down, while 37 days sufficed for its return to the surface. 

 At Skate Island practically the same time was taken for the temperature of 50° to 

 reach 64 fathoms, which was the maximum attained ; and early in August the 

 temperature of 54° worked clown at both stations to the same small depth of 8 

 fathoms. 



In 1888 the observations are complete enough to show that the surface was over 50° 

 from July 24th to October 18th, while the maximum depth, reached by that temperature 

 on August 24th, after 31 clays, was 12^ fathoms. 



The maximum temperature at the bottom, due to the summer's heat of 1886, was 

 reached on February 24th, 1887, 194 days after the elate of the surface maximum, and 

 54 clays after the succeeding surface minimum. The minimum at the bottom occurred on 

 April 15th, 50 clays after the maximum. The summer's heat of the exceptional year 

 1887 reached the bottom more rapidly, the maximum occurring there on December 31st, 

 just 169 clays after the surface maximum, and 45 days before the surface minimum. 

 The minimum at the bottom was on April 24th 114 days later than the maximum. 



In the Channel the bottom and surface maxima are simultaneous, in the Arran Basin 

 at Skate Island the average of two years showed the bottom maximum to be retarded 

 63 clays, while in Loch Fyne, at Strachur, the retardation averaged 182 days, or 

 practically six months. This is a very striking illustration of the influence of increasing 



