120 



Mi HUGH ROBERT MILL ON THE 



with 100 : 115 in the Channel, 100 : 100 in the Arran Basin, and 100 : 91 in Loch Fyne, 

 and shows that shallowness and exposure to land influences tend to increase the rapidity 

 of heating, and probably to retard cooling. The cooling of 1887-88 was evidently 

 anomalous, but it may only exaggerate what seems to be a normal disparity. 



The mean rate of change of temperature per day, calculated from the figures in Table 

 XLI V., is 0°'074 for the whole mass of water, a change of temperature of 1° requiring 

 on the average 13^ days to be effected. The bottom layer of 10 fathoms (10-20 fathoms 



Table XLV. — Period of Heating and Cooling, and Daily Rate of Change of Temperature 



in the Clyde Sea Area. 



Division. 



Warming, 



1886. 



Rate 

 per day. 



Cooling, 

 1886. 



Rate 

 per day. 



Warming, 

 1887. 



Rate 

 per day. 



Cooling, 

 1887. 



Rate 

 per day. 



Warming, 



1888. 



Rate 

 per day. 



Channel, 



147 days 



0°-090 



171 days 



0°-065 



189 days 



0°-065 



217 days 



0°-062 







Arran Basin, . . 



165 „ 



0°-058 



151 „ 



0°-053 



186 ,, 



0°-046 



199 ,, 



0°-049 







Loch Fyne, . . 



168 ,, 



(T-047 



156 ,, 



0°-039 



206 „ 



0°-037 



184 ,, 



o, 045 



170 days 



0°-033 



Gareloch, . . . 



153 ,, 



0°-081 



166 „ 



0°-070 



145 „ 



0°-107 



251 ,, 



0°-064 



168 „ 



0°-079 



Loch Goil, . . . 



19S „ 



0°-038 



144 „ 



0--040 



160 „ 



0°-058 



210 ,, 



o, 046 



180 „ 



0°-043 



in depth) changed its temperature at the average rate of o, 072 per day, or 1° in 14 days. 

 The curve of variation in the rate of change of water-temperature with time which is 

 not reproduced brings out the peculiarly prolonged period of falling temperature in the 

 spring of 1888. 



The relation of air-temperature to water-temperature is also shown in fig. 46, where 

 it is seen that the air-curve cuts the water-curve at the maximum in descending, and 

 rather after the minimum in ascending. This proves, as in the case of Loch Fyne, that 

 contact with air colder than the surface water arrests the process of heating by 

 radiation after the autumnal equinox, while radiation seems to check the loss of heat 

 even in contact with colder air after the vernal equinox. It is also remarkable that the 

 maximum rate of water-heating occurs nearly a month before the maximum air-tempera- 

 ture is reached, while similarly the most rapid cooling occurs a month or so before the 

 minimum of air-temperature. This shows that radiation and the other influences 

 which produce changes of air-temperature produce the changes of water-temperature 

 not consequently but simultaneously, if not previously. 



The air-temperature at Helensburgh (considering monthly means) was above the 

 mean temperature of the water of the Gareloch for 154 days in 1886, for 94 days in 

 1887, and for 155 days in 1888. The air was colder than the water for 245 days in 

 1886-87, and for 250 days in 1887-88. Speaking generally, this gives the air warmer 

 than the water for four and a half months from April to August, and colder for the 

 remaining seven and a half months. For the two complete seasons included in the years 



