CLYDE SEA AREA. 127 



the isotherm of 50° reaching its greatest depth, 18 fathoms, on November 12th, having 

 a much more marked diagonal trend than in Loch Fyne. The rate of descent also was 

 far slower, 123 days being required for 18 fathoms, contrasted with 110 days for 105 

 fathoms at Skate Island, and 92 days for 23 fathoms in Loch Fyne. In 1887 the surface 

 was above 50° from May 10th to October 25th, and the temperature of 50 c reached 

 its greatest depth, 20 fathoms, on November 28th, again long after the date when the 

 isotherm had passed out at the surface during the winter cooling. On this occasion 

 202 days were required to carry the isotherm down to 20 fathoms (although 92 clays had 

 taken it to 19 fathoms), compared with 123 daj^s for 30 fathoms in Loch Fyne, and 123 

 days for 60 fathoms at Skate Island. In 1888 the rather incomplete observations 

 showed that the surface was above 50° from June 24th until October 23rd, and the 

 isotherm reached its maximum depth of 11 fathoms on September 3rd, after 71 days, 

 compared with 31 days for 12^ fathoms in Loch Fyne. 



The time-depth diagram also serves to measure the retardation of the seasonal phase. 

 In 1886 the surface maximum occurred on September 25th, while the bottom maximum 

 was delayed until January 15th, 1887, an interval of 112 days, or 285 days after the pre- 

 vious bottom minimum. The retardation was at the rate of 2*5 days per fathom, com- 

 pared with 2*8 days per fathom in Loch Fyne. The bottom minimum occurred on 

 April 15th, only 60 days after the surface minimum, and 88 clays after the bottom 

 maximum. The maximum of 1887 occurred 241 days later, on December 12th, about 

 120 days after the surface maximum ; on this occasion the retardation per fathom was 

 2*7 days, compared with 2*3 days for Loch Fyne. The next bottom minimum came 

 after 109 days apparently, probably simultaneously with the surface minimum. The 

 average retardation of the maximum for the two periods was 116 clays, or practically 

 four months, as compared with six months in Loch Fyne, and two months at Skate 

 Island. The average ratio of the times of heating and cooling at the bottom was 

 263 : 84 days, or roughly, 3 to 1. 



Observations at Lochgoilhead. — At this place observations were made a little to the 

 south of the steamer pier in mid-channel, just at the commencement of the abrupt rise of 

 the loch-bed at the head. The depth was about 25 fathoms, but observations were occa- 

 sionally made opposite the pier where the depth was from 12 to 10 fathoms. 



The density of water was as follows : — 



Bottom. 

 1-02440 

 102465 

 102400 



The average percentage of pure sea- water at the surface was 8 2 "6, at the bottom 93*8, 

 and in vertical section 91*9. The probable normal value in the vertical section was 91 '4. 

 The distribution of temperature resembled on the whole that at Stuckbeg, with the 

 differences always associated with shallower water and a position close to the upper end 

 of a loch basin. 





Surface. 



Mean, 9 observations, . 



102236 



Maximum, 



102427 



Minimum, 



101797 



