270 Part III.— Fifteenth Annual Report 



Densities of Water at Otter, 8th September 1896, 17 5 S 17 5. 



Hour, . 



9.20 



10.15 



11.15 



12.15 



13.15 



14.15 



15.15 



16-15 



17.15 



IS. 15 



Surface, 



1 0251 



1-0249 



1-0250 



1 0251 



1 0253 



1-0250 



1 0249 



1 0249 



1-0251 



1-0254 



Bottom, 



1-0257 



1-0256 



1-0255 



1-0257 



1-0256 



1 0254 



1-0255 



1-0255 



1-0256 



1-0256 



Densities as above on 9th September 1896. 



Hour, 



6.20 



7.15 



8.15 



Surface, . 



1-0260 



1-0255 



1-0255 ; 



Bottom, , 



1-0255 



1-0254 



1-0255 



The rates of current, as determined by means of the floating chip on 

 the 8th, were as follows ; the wind made such observations quite valueless 

 on the 9 th : — 



Flood. H.W. Ebb. L.W. 



Hour, . . 9.20 10.15 11.15 12.15 13.30 14.20 15.15 16.15 17.15 18.15 

 Miles per hour, f § f | £ 1 2 3 1| Q 



Tibial Observations at Furnace. — -Nine observations were made in the 

 middle of the channel, off Furnace, but unfortunately only one of these 

 was fairly representative of flood-tide conditions. The others all dealt 

 with the ebb, about which they supply considerable information. Six of 

 the soundings, including two cross-sections, are recorded in Table VI. ; the 

 other three, each of them including a section across the loch, are giveu in 

 a separate table (Table IV.). The three sections were made at high-water, 

 half-ebb, and low-water respectively. The conditions at the time were a 

 uniform thin layer of warm surface water (over 53°) over the whole Gortans 

 and Upper Basins, a homothermic stratum at about 52°*5 filling Gortans 

 Basin and the lower end of the Upper Basin below Furnace to a depth 

 of 20 fathoms ; and below that a cold mass filling the deeper part 

 of the Upper Basin. The effect of the ebb-tide was not to disturb the 

 upper warm layer, which evidently flowed unchecked into the Gortans 

 Basin ; but there was at half-ebb a very marked upwelling of the cold 

 water from the depths of the Upper Basin, analogous to the upwelling of 

 cool water from the Arran basin at Otter during flood-tide. Thus, the 

 bottom water at the deepest point at Furnace was 1° colder at half-ebb 

 than at high-water, showing an updraught of water from at least 7 

 fathoms deeper. The possibility of this effect being produced by observ- 

 ing in different positions was guarded against by fixing the position each 

 time by accurate cross-bearings, and checking by the depth. By low-tide 

 the deep temperature had risen half a degree, probably to a large extent 

 by mixture of the water, possibly in part by a backward swing when the 

 outflowing current slackened. The study of the cross-sections amply con- 

 firmed these conclusions drawn from the central station observations. 

 They show that at any given depth the water is always slightly colder at 

 the sides than in the centre of the channel, but that the invasion of colder 

 water in the greater depths during ebb-tide takes place throughout the 

 whole breadth of the loch. 



It would be extremely desirable to repeat and extend these observations 

 in a way clearly suggested from the above preliminary discussion ; but, so 



