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, Druiikie, 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. 



Locli 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 llth it had again risen to 50*1. 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 0< 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. 



