CLYDE SEA AREA. 71 



The East Arran Basin shows the greatest range of temperature and a slightly earlier 

 phase than the others. This is brought about by a higher maximum, all the curves 

 comma- close together at the minimum. At the maximum the curves are most widely 

 separated, the West Arran Basin coming second in each case, and the Central branch 

 last. The three curves preserve this order during the annual rise of temperature, but 

 reverse it while falling and at the minimum, when the Central branch is warmest and 

 the Eastern coldest. The curves cross in April while the temperature is rising, imme- 

 diately after the minimum, and in October or November when falling, shortly after the 

 maximum. . The mean temperature for each month, taken from the curve, is given for 

 the branches and the Basin as a whole in Table XXIII. 



Fig. 25, Plate XX VII., showing the seasonal variation of the temperature of the air as 

 the average of the whole Clyde Sea Area, of the whole mass of water in the Arran Basin, 

 and of the superficial layer of 5 fathoms, may be usefully compared with fig. 5, Plate 

 XXIII. , giving the same data for the Channel. It must be remembered, however, that 

 although the Arran Basin results are supported by much more numerous data than 

 those of the Channel, the regular homothermic change in the Channel makes its curve 

 probably more correct than that of the Basin. 



Comparing the temperature of the whole mass of water, we see that it started on April 

 15th, 1886, from the same minimum as the Channel, 42° ; and on October 1st it reached 

 its maximum value of 51°'6 (3°"4 lower than the Channel, and twenty days later). This 

 rise of 9°*6 in 165 days corresponds to a mean storage of o, 058 per day, one-third less 

 than the Channel rate. The rate of fall of temperature increased much more gradually 

 than in the Channel. By March 1st, 1887, the minimum temperature, 43°*6, was reached, 

 slightly lower and a little earlier than the Channel. This corresponded to a loss of 8° in 

 151 days, or at the rate of o, 053 per day, a rate one-fifth less than that of the Channel. 

 On September 2nd, 1887, the maximum of 52° # 2 was reached (4° colder and 16 days 

 earlier than the Channel), a rise of 8°"6 in 186 days, at the rate of 0°*046 per day, 

 the ratio to the Channel conditions being the same as in the previous year. The fall of 

 temperature proceeded more gradually, the minimum, 42°'5, being reached on March 

 20th, 1888, 9°'7 being lost in 199 days, or at the rate of 0°-049 per day. 



The near approach to equality in the time of heating and cooling of the mass of 

 water in the Arran Basin is remarkable when compared with the disparity shown in the 

 Channel. 



Warming 1886. Rate. Cooling 1886. Rate. Warming 1887. Rate. Cooling 1887. Rate. 



Channel, . . 147 days, +0°-090 171 days, 0°-065 189 days, 0°'065 217 days, 0°-062 

 Arran Basin, 165 days, + 0°058 151 days, 0°053 186 days, 0°046 199 days, 0°-049 



The rate of change of temperature in the Arran Basin varied, as the curve shows, 

 more regularly and uniformly than in the Channel. Whereas the periods of heating 

 and cooling in the Channel were as 100 to 115 on the average of two years, they were 

 equal on the average in the Arran Basin. The minima were synchronous, but the 



