THE FRESH-WATER LOCHS OF SCOTLAND. 
25 
both on the surface and at intervals below the surface, down to the 
bottom. All the serial temperatures taken in Lochs Katrine, Arklet, 
Achray, Drunkie, Vennachar, Doine, Voil, and Lubnaig have been 
collected together in the table,* and, in order to make the record more 
complete, the temperatures taken by Jardine in 1812 and 1814 in Loch 
Katrine are given in the first two columns. 
Loch Katrine . — The surface temperatures taken in Loch Katrine 
during the seven days from June 5 to 11, 1897, are extremely interest- 
ing, as illustrating the effect of the wind. The range of temperature 
during this time was 12 J°, from 45°'3 to 57°'8, the highest reading being 
observed at Trossachs pier on the evening of June 5, and the lowest at 
the same place on the evening of June 9. This was evidently the 
result of a strong east wind, which commenced to blow on the 6th, 
and continued from the same direction till the 9th, blowing the warm 
surface water before it from the east towards the west end of the loch, 
while colder water from below was drawn up to the surface at the east 
end of the loch to take its place. The gradual cooling of the water at 
the east end of the loch is well shown by the temperatures taken at 
Trossachs pier from day to day ; thus at 6.30 p.m. on June 5 the 
temperature was 57°‘8; at 11.30 a.m. on the 6th it was 56°'2; and at 
4 p.m. 55°’3 ; at 7 a.m. on the 7th it was 49°’2 ; at 10.30 a.m. on the 
8th it was 46°'3 ; and at 7.15 p.m. on the 9th it was 45°'3. By 9.30 
a.m. on the 11th it had again risen to 50°'l. The effect of the wind was 
also shown by a series of surface temperatures taken from the steamer 
on its way from Stronachlachar pier to the Trossachs pier on the evening 
of June 9 : thus at Stronachlachar the temperature was 52°'6; near the 
waterworks, 52°'0; near Letter, 49°’6; near Brenachoil, 48°'8 and 
48°'0 ; near Ellen’s isle, 47°-4 and 47°-0 ; and finally at Trossachs pier, 
45°'3. It will thus be seen that it is very unsafe to rely on a single 
observation at one spot as giving a sure indication of the temperature of 
the surface waters of a loch as a whole at any given season. A year later 
(from June 4 to 9, 1898) the temperature of the surface waters of Loch 
Katrine was not observed to fall below 50°. On November 26, 1897, 
the surface temperature varied only from 46°*8 to 47°*4, and on April 
13 and 15, 1899, from 41°-2 to 42°'7. 
The serial temperatures in Loch Katrine are shown graphically 
in the accompanying curves (Fig. 13), which exhibit the march of tem- 
perature in the waters of the loch throughout the year. The curve for 
April shows that the water from top to bottom has a temperature rang- 
ing between 41° and 42° Fahr. In the two curves for June the heating 
effect of the sun on the surface layers is indicated, but in depths beyond 
* Temperature observations in the surface waters of some of the lochs under considera- 
tion have been taken by Mr. Thomas Scott, and the results published in the Annual Reports 
of the Fishery Board Jor Scotland. 
