140 DR HUGH KOBEET MILL ON THE 



XVI. 19th December 1887. — A strong northerly wind was blowing down the loch, 

 and all the isotherms showed, accordingly, a strong seaward dip. The water at the head 

 of the loch was salt and clear, and was the warmest surface-water in the section, 48° 

 compared with 43° "7 at the mouth. The run of the isotherms suggests that the deep 

 water was being drawn up all along the section, and the reverse dip of the lower isotherms 

 of 48° at the mouth, indicates the drawing in of colder water along the bottom. 



The three sections illustrate admirably the rapidity with which the entire vertical 

 circulation of a long narrow basin may be reversed. 



XVII. 8th January 1888. — The water had by this time assumed a nearly homo- 

 thermic condition, and had greatly cooled. The one prominent isotherm in this section, 

 however, dipped strongly seaward. The wind was variable and squally, shifting from 

 north-west and north-east to south. 



XVIII. 27 th January 1888.- — The wind was blowing a heavy gale from N.N.W. and 

 north when the observations for this section were taken, and the solitary isotherm (45°"5) 

 it bears, dipped seaward, as might be expected. The extreme range of temperature was 

 from 45° '0 to 45°"8, and this approximation to homothermicity was undoubtedly largely 

 due to the mixing effect of the strong wind. 



XIX. llth February 1888.— This is another almost homothermic section, showing, 

 by a curious coincidence, a wedge-shaped inclusion of warmer water nearly in the same 

 position as in February 1887 (see Section VIIL), and, like it, bounded by the isotherm 

 of 45°. For the rest the water was simply homothermic, its extreme range, but for this 

 inclusion, being from 44°*4 to 44 0, 8. The wind was northerly and light. 



XX. 2§th March 1888. — Here a minimal section presents an unusually complicated 

 character, the central mass of the water being a little warmer than 43°, while above and 

 seaward the water cools to 42 0, 1, and below it cools to 42°"8. The total range is so 

 small that one cannot found any argument upon the run of the isotherms. There was a 

 light north-east wind. 



XXI. 9th June 1888. — This is a mere fragment, showing the surface layers stratified 

 by perfectly horizontal isotherms. The wind on this occasion was a light breeze from the 

 west, and Dr Murray found that the surface water along the side of off-shore wind was 

 about 48°, and on the side of on-shore wind about 51°. In the fraction of axial section 

 the surface was at 49°*5. This shows how a transverse disturbance of the water may 

 give no trace in a longitudinal section, even while very considerable mixing may be in 

 progress. 



XXII. 20th September 1888. — Atypical "heating" section with isotherms on the 

 whole horizontal is here given. Above 15 fathoms the isotherms were concave upward, 

 and below that plane they dipped seaward, indicating possibly an inward current of nearly 

 homothermic water over the Bute Plateau, and a slight upwelling at the head, which does 

 not, however, extend quite to the surface. The wind was light from the north-east. 



XXIII. 20th October 1888. — This section shows a very close approach to homo- 

 thermicity in the initial stage of cooling, the extreme range being from 50 o, 5 on the sur- 



