NATURAL HISTORY OF BRITISH SALMONID/E. 123 



points to be considered are, a, the placing of the ladder in the 

 most suitable part of the weir ; //>, the proper incline of the 

 ladder ; and, <r, the supply of water which is admitted to it. As 

 Air; Horsfall once wrote to me. no two weirs are alike, and in 

 his experience the proper position of the ladder can only be 

 shown by actually watching the habits of the fish at the darn, 

 and the points towards which they naturally head in their efforts 

 to ascend. There is a limit to the steepness of an efficient fish 

 ladder one in four being, I believe, the maximum slope which 

 can be safely calculated upon Next to this the point of 



greatest importance is that the ladder should be supplied with 

 a greater flow of water in proportion than that running over any 

 other part of the weir, as when salmon and any other fish in 

 their ascent up the river meet with any obstruction they seem 

 instinctively to be attracted to the part where the stream is the 

 strongest. 



The engraving is taken from the first model fish ladder 

 which was approved by the Inspectors of English Salmon 

 Fisheries and officially recommended for a weir thirty feet 

 broad and six feet high. The principal dimensions are as 

 follows : 



