94 DR HUGH ROBERT MILL ON THE 



steadily to 44° '2 at the bottom. In this section we see last winter's cold still undis- 

 sipated below, but separated from this winter's cold, which is coming in above, by the 

 remains of the summer heat occupying an intermediate position, the freshness of the 

 surface water effectually resisting the formation of convection currents. 



Section VI, 29th-30th December 1886. — Great and general cooling is shown here. 

 Outside, the surface is at 46° - 6, the bottom at 47° "4, but just outside the Otter barrier a 

 patch of bottom water above 48° occurs. As no observation was made at Kilfinan, the 

 extent of this can only be guessed. 



From Gortans the isotherm of 46° runs almost straight to the head of the loch at a 

 depth of 5 or 6 fathoms, the surface temperature falling below 36°, without, however, 

 sensibly chilling the water below on account of surface freshness. Ice, resulting from 

 the freezing of floating rain or thaw water from land, prevented an examination of the 

 head of the loch on this occasion. The isotherm of 47° slopes up from Minard barrier 

 until it comes close to 46° at Inveraray and beyond. A maximum line of about 47°'5 

 runs along the loch at about 20 fathoms, and beneath that depth the temperature falls 

 gradually to 44° "8 on the bottom. The isotherms, as a whole, converge toward Minard, 

 and diverge widely toward the head. 



Section VII., £th-5th February 1887. — Outside, the temperature is somewhat irregular, 

 varying between 44° and 45° from surface to bottom, and the Gortans Basin forms part 

 of the Arran Basin so far as temperature is concerned. A slight upwelling of warmer 

 water from beneath appears at Otter. Inside, the temperature increases from 43° or less 

 on the surface pretty uniformly to 46°*5 at 45 fathoms, then diminishes very gradually 

 to 45°*7 on the bottom. The isotherms generally follow the contour of the bed of the 

 Basin, except for a slight rising of the upper isotherms at Inveraray. 



It is noticeable, not only in this, but in almost all the sections, that Gortans Basin 

 is part of the Arran Basin, receiving its surface water, and that the special enclosed 

 character of Loch Fyne begins at Minard. 



Section VIII, 29th March 1887. — Here a condition of remarkable uniformity 

 prevails. Practically the total range is from 44° to 45°. The surface and bottom of the 

 Upper Basin are at, or slightly above, 45°; the intermediate layers are nearly 44° "5 ; 

 while the Gortans Basin and the Arran Basin contain water at, and colder than, 44° in the 

 middle. 



Here surface heating seems to be just beginning, and a general equalisation of tem- 

 perature has occurred similar to that of April 1886, although 2° warmer. 



Section IX., IQth May 1887. — The Gortans Basin is now filled with water of nearly 

 uniform temperature, 46° on surface, 45° on bottom. Outside, it is 46°"3 on the surface, 

 and sinks to an intermediate minimum slightly under 44°. Inside, the surface layers 

 grow warmer toward the head in a remarkable way, the warming, though not spreading 

 down the loch, extending to several fathoms in depth, and the temperature exceeding 

 50° near Cuill. The isotherm of 45° runs pretty straight from Minard to Cuill at a 

 depth of 20 fathoms. Below that the water cools to a minimum, about 44° at 40 



