138 THE LIFE OF THE SALMON 
not greatly different, except possibly at the extreme 
upper ends. When, however, the fish essay to 
ascend farther, they are met by distinctly colder 
water, and their progress is at once checked, till, the 
particular time when the winter conditions of those 
upper rivers having passed, they find themselves 
once more willing to travel and overcome obstacles 
in their course. The rivers Garry and Orchy are 
the early rivers of their districts, therefore, because 
all the lower waters are of such a relatively high 
temperature as induces rapid ascent, while the Garry 
and Orchy are of a temperature which in Scotland 
produces a check upon early ascent. Added to this 
we must not forget that small falls exist in each 
case. Spring fish are no jumpers till summer con- 
ditions have come about. 
Apply this interpretation to the Tay and its upper 
water, the Dochart, and we see that while the main 
river, with its course of some 50 miles, receives 
various large tributaries, and has a general tempera- 
ture in the first four months of the year which at 
times induces fish to run and at times checks their 
running, thus naturally securing to this fine river a 
distribution of spring fish, the Dochart—which has 
a fall upon it a short distance above Loch Tay—is 
exactly analogous to the waters of the Garry or 
Orchy above their respective falls. Fish therefore, 
if we argue by analogy, should, as in the Garry and 
Orchy, ascend the Dochart fall when the wintry 
conditions have passed. This is, as a matter of fact, 
exactly what happens, for the Loch Tay fish begin 
to go up the Dochart in May. 
