THE HABITS OF THE SALAION. 25 



mile and a half in circumference. There is a course 

 of about twenty miles between the loch and the 

 tideway. There is also a course of about sixteen 

 miles between Loch Naver and the tideway. We 

 know that in both of these rivers salmon are found 

 in the month of January and sometimes even earlier. 

 Some years ago there were cruives in the Thurso, 

 but for some time past they have not been used, 

 and now there are no such engines in either river. 

 But the habits of the salmon that frequent them 

 differ considerably. For instance, they run into 

 Loch Naver as early as January and February, but 

 not one single fish goes into Loch More until quite 

 the end of March or beginning of April. It is well 

 known that in winter and early spring the tem- 

 perature of water in big, deep lakes, and rivers which 

 are fed by them, is much warmer than the waters 

 of small shallow lakes ; and again, the temperature 

 of water in deep large lakes is lower than that of the 

 sun-heated rivers during the summer months. This 

 accounts for the fact that salmon run earlier into 



