494 Dr KNOX on the Natural History of 



circumstances under which my observations were made, I have every reason to think 

 the conclusions legitimate. The broad and deep streams of the Tay near Perth, do 

 not seem to me favourable for experiments of this kind, and, by their very extent of 

 waters, widens the question, rendering it of course every moment more and more com- 

 plex. On the other hand, the narrow stream in which my observations were made, pro- 

 portionally, as it were, contracted the question, and brought it more within my reach. 

 Still it is true that no one has succeeded in observing the development of the egg, and 

 the growth of the smolt, to the length of 6 or 7 inches ; or, in other words, proving, by 

 a direct experiment, performed in vessels placed under their immediate observation, that 

 the fishes abounding in salmon rivers, during the months of April and May, are really 

 salmon-smolts, and proceed from the ova or salmon-eggs deposited under the gravel of 

 these rivers during the preceding winter. 



The second question of difficult solution is that regarding the return of the fry from 

 the ocean to the salmon river, and in what form, and at what period, the salmon does 

 first return from the sea : I have already remarked, that upon this question there is not 

 >i single authentic observation. 



4. Alteration of the Nature of Rivers by Drainage. 



THE system of drainage practised over the Cheviot and Lammermuir mountain 

 tracts is very extensive, and must have considerably modified the nature of the rivers 

 connected therewith ; but whether this really influences the deposition of the salmon ova 

 may be questioned : for -it is worthy of remark, that at the period of the year when the 

 salmon is busiest in the propagation of its species, the rivers and tributary streams are 

 generally in their very smallest condition ; and hence, and also for other causes, it must, 

 I think, generally happen, that the salmon select, almost in an unerring manner, the 

 never-failing stream under which they deposit the egg. All that has been said by in- 

 genious persons about the destruction of salmon ova, in consequence of the drying up 

 of streams, is very plausible and ingenious, but without foundation in positive personal 

 observation. The difference between ingenious conjectures of this kind, and the results 

 of personal positive research by correct and authentic observers, is but little understood 

 by many persons, who, nevertheless, think tolerably well upon ordinary topics. These 

 persons seem incapable of that careful mental process which requires us to go back and 

 inquire into the sources of our information and opinions. 



5. Can the Supply of Salmon be increased ? Has it diminished ? 



THE supposed abundance of salmon in former times and their supposed scarcity now, 

 seems to me a mistake. 



1st, An occasional scarcity of salmon proves nothing ; nor even a lengthened scarcity. 

 In the vast waters of the Columbia, there is said to be a scarcity every second year *, 

 of a fish much resembling the salmon both in habit and quality as food. But the un- 

 due fishing or poaching of the tributary streams of the Columbia, the taking of smolts 

 in too great quantities, the evils occasioned by mill-dams and manufactories, the in- 



* Travels to the Banks of the Columbia, by Mr Boss Cox. 



