90 DR HUGH ROBERT MILL ON THE 



practically continuous between, a very striking case of complete mixture by wind 

 without loss or gain of heat. 



Curves 18, 19, 20 were observed on 24th, 25th, and 27th August 1888. The obser- 

 vations were all made in the afternoon, and in about the same state of tide. The wind 

 was from a southerly quarter, very light on the 24th, fresh on the 25th, and strong on 

 the 27th. It was practically an up-loch wind. On the 24th the mean temperature was 

 52 0, 7, on the following day 52°. The surface temperature had meanwhile risen from 60°"8 

 to 62°"3, the bottom temperature had fallen from 49°'4 to 47°'4. The depth was the same, 

 15 fathoms. The curves crossed at 1\ fathoms, showing slight heating in the upper 

 layers, and very marked and increasing cooling in the lower. The fall of 0°7 in mean 

 temperature was thus the result of great incursions of cold water from beneath, while 

 warm surface-water was flowing in above. This serves to suggest a double action on the 

 part of the south wind as shown (fig. 39, Plate XXIX), similar to the double action 

 noted in the case of the Gareloch cross-section. Between the 25th and 27th, 1°'6 of 

 warmth was added. All above 2 fathoms was greatly cooled, all below it still more 

 greatly heated, the same temperature occurring about 3 fathoms deeper throughout than on 

 the 25th. This might indicate that the continuance of the up-loch wind had overcome 

 the double action, and was now driving the warmer water to the greater depths, and 

 drawing up some cooler water to the surface. Figure 40, Plate XXIX, shows a possible 

 exjDlanation of this action. All above 1 fathom was cooler than on the 24th, so was all 

 below 10 fathoms ; but between 1 and 10 fathoms there had been a great rise of tempera- 

 ture. This matter will be treated more fully when considering the Temperature Sections. 



Temperature Sections of Loch Fyne. — A series of vertical sections along the axis of 

 Loch Fyne were drawn with the vertical scale exaggerated 150 times as compared with 

 the horizontal, in order to enable the isotherms of every degree Fahrenheit to be con- 

 veniently represented. The section extends from Cuill to near Skate Island, in order 

 to show the relation of Loch Fyne to the Arran Basin. From the 23 sections which 

 have been drawn it is possible to obtain some insight into the thermal transactions of the 

 water in Loch Fyne as a whole, and to calculate the mean temperature of the whole body 

 of water at different times. They are reproduced in Plates XII. to XV. 



Section I, 20^ April 1886. — This shows the minimum and most uniformly 

 distributed temperature of the entire series. Temperature varied but little from 42°, 

 with a general seaward dip of isotherms ; 42° occurred deeper at Inveraray and Strachur 

 than anywhere else in the section. The prevailing wind at the time of observation was 

 a fresh breeze down-loch. In all cases the surface was slightly warmer than the depths. 



Section II, 2lst-22nd June 1886. — The prevailing wind was on the whole westerly, 

 <>r nearly up-loch, and light, The arrangement of temperature was remarkable. The 

 surface was about or over 48° everywhere, except at Otter, where there was marked 

 upwelling of colder water. The isotherm of 45° preserved an average position of about 

 10 fathoms, and the whole Gortans Basin was filled with water above 44°. The 



