its 



DR HUGH ROBERT MILL ON THE 



gradually mixing with the mass down to the bottom. There is, indeed, a certain amount 

 of mixture, as is proved by the variations in the salinity of the deep water. How far 

 this is due to tidal action we cannot say. Wind is certainly a more powerful agent for 

 settiug up vertical currents in the water than tide is, but a steady wind in one direction 

 rarely lasts long enough to produce its full effect. The tides, on the other hand, act 

 continuously, and I have by further consideration been led to modify the opinion stated 

 in Part II. p. 706, that tidal influence was insignificant as leading to the formation of 

 deep currents in the Upper Basin. I do not find in the temperature observations enough 

 data to found an exact theory upon, and the precise share of steady tidal action and 

 spasmodic wind-action in stirring the depths of the Upper Basin must remain for the 

 present undetermined. 



Table XXXIV. shows that even with constant temperature there is not stagnation 

 at the bottom. 



Table XXXIV. — Bottom Salinity and Temperature. — Strachur. 





April 



1886. 



June Aus;. 

 1886. 1886. 



Sept. Nov. 

 1886. | 1886. 



Dec. 



1886. 



Feb. 

 1887. 



March 

 1887. 



May 



1887. 



June 

 1887. 



July 



1887. 



Sept. 

 1887. 



Average. 



Density at 

 60° F. 



Temperature 

 in situ. 



1-02450 

 41-9 



1-02481 



44-1 



1-02517 

 44-2 



1-02483 

 44-1 



1-02422 

 44-2 



1-02172 

 44-7 



1-02441 

 45-9 



1-02430 

 45-5 



1-02447 

 44-7 



1-02477 

 45-2 



1-02479 

 45-2 



1-02472 

 45-3 



1-02465 

 44-6 



Here we see that there were variations in the bottom salinity from its minimum to its 

 maximum value during the period of constant bottom temperature, June to November 

 188G ; and this fact shows that the exchange of water with the outside must have been 

 very uniform and gentle indeed. The intermediate belt of minimum temperature would 

 provide in June and August a means of chilling the warm dense Gortans Basin water as 

 it sank, so that it would not carry its original temperature down with it, but between 

 September and November no such explanation offers. The period June to September 

 1887, when the temperature was constant, was also characterised by uniform salinity, 

 and, but for the contradiction of the previous year, would have justified a presumption 

 that constant bottom temperature indicated stagnation. 



Seasonal Variations of Temperature in the Mass of Water in Loch Fyne. — From 

 the temperature sections the mean temperature of the whole mass of water in Loch 

 Fyne from Otter to the head was calculated for each trip in the manner already 

 explained (p. 10). The temperature of each layer of 10 fathoms was estimated by 

 measuring the areas between successive isotherms, and the resulting figures were 

 " weighted " by multiplying each with a factor representing the relative volume of the 

 layers, and dividing the sum of the products by the sum of the factors. The factors in 

 the case of Loch Fyne were : — 



Layer in fathoms, 0-10 10-20 20-30 30-40 40-50 50-60 Over 60 

 Factor, . . 15'5 133 95 4-9 3*0 21 10 



