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Part III. — Fifteenth Annual Report 



and over 54° in temperature ; above Inveraray the warm layer thinned 

 away ; below Gortans it deepened considerably. 



The distribution of temperature throughout the mass on September 

 10th was substantially the same, but the differences were of considerable 

 interest, though of small amount. The water in Gortans Basin, still 

 almost homothermic, had warmed by one degree ; the surface film of warm 

 water had disappeared from the Upper Basin ; but, on the other hand, the 

 lower layers down nearly to the bottom had warmed up perceptibly. On 

 both occasions the convergence of isotherms from above and below at 

 Furnace on the vertical section was well marked, as indeed it was usually 

 found to be in the earlier observations. This seems to indicate a sort of 

 swing or surge in the mass of the water at this point ; and one of the 

 principal objects of the cruise was to ascertain whether there was aiay 

 tidal variation in the temperature near the bottom off Furnace. These 

 temperature observations lose some of their value by not being simul- 

 taneous ; thus, instead of each longitudinal section being made at the same 

 tidal phase, that of September 4th was begun at the head of Loch Fyne 

 at high-water, and finished off Kilfman at low-water, passing Furnace at 

 half-ebb. That of the 10th commenced at the head of the loch about 

 half-flood, passed Furnace at high-water, and concluded at Otter about 

 half-ebb. These differences of tidal phase had no great effect on the 

 arrangement of the layers of water, but the full consideration of the 

 observations will possibly show that there is a distinct, though gentle, tidal 

 vibration throughout the mass. The wind on the 4th was easterly, or, in 

 the main, blowing down the loch, and usually very light. On the 10th the 

 wind was south-westerly, i.e., blowing, on the whole, up the loch, and very 

 light. On the 9th an easterly, or, in the main, down-loch breeze had 

 beeu blowing freshly all day, rising at times to the force of a gale, and 

 this may have been instrumental in mixing the superficial layers of water, 

 as found on the 10th. 



Tidal Observations at Cuill. — These observations comprise 19 

 temperature soundings, recorded in Table IIL, and taken on September 

 3rd in mid-channel, opposite Cuill, in the shallow water at the head of 

 Loch Fyne, just on the edge of the abrupt descent to considerable 

 depths. Slightly deeper water is found on both sides of the point of 

 observation, and the river Fyne enters the head of the loch about a 

 mile distant. As the tide ebbed, the warmer and fresher water from 

 the river began to preponderate ; and as the tide rose again, the colder 

 water from down the loch mixed from below with the river water, and 

 drove it back, restoring the same conditions as prevailed before. The 

 tidal action of the head of the loch is, in fact, simply that of an estuary 

 receiving a relatively small stream. It was observed that the water did 

 not increase in depth steadily with the rising tide, but, in a series of 

 pulses, the temperature changes corresponding. The weather throughout 

 this series of observations was warm and overcast, with no wind. 



Tidal Observations at Otter. — Table V. gives the data of 13 tempera 

 ture soundings made from the 1 Garland ' anchored in the tideway, off 

 Otter Beacon, in a position indicated by the Beacon on with Baltimore 

 House, and two unnamed headlands on the west shore in line. It was 

 rather to the westward of the deepest part of the channel, and the depth 

 was between 16 and 17 fathoms. Temperature observations were made 

 each hour at the surface, and at 1, 6, 11, and 16 fathoms, five ther- 

 mometers being used, so that all the temperature observations for each 

 sounding were exactly simultaneous. Samples of water were also taken 

 from surface and bottom, and the densities observed by one of the 



