142 



SEASON 1874-75. 



be 2 feet deep. This always leaves a sufficient space clear for the 

 water to pass, and if there is a fine screen behind, the 6 inches is 

 ample for the water to rise between before passing the zinc (Fig. 96). 

 All screens less than half-inch should be of zinc in trout-culture. 

 Of course, in rearing sparlings (Osmerits eperlanus), smaller screens 

 still are necessary, and fine copper wire must be procured. Where 

 the wire-screen has only to confine mature trout, it must be 

 closed underneath ; where there is also a zinc screen, it should be 

 left open. The reason frost is powerless against this screen is, the 

 depth of it is insufficient to be below any ice forming on the sur- 

 face. In Scotland 18 inches is the most I ever knew. The water 

 between the screen and the overflow does not freeze, the current 

 being too strong. Below is a sketch of the screen (Figs. 97, 98). 



FIG. 97 scale 



FIG. 98 scale 



The overflow of the dam-sluice was utilised for a set of rear- 

 ing-boxes thus : A spout was fixed along the masonry of the 

 section of the dam cut by the overflow from the sluice ; a tray 

 was fitted to the back of the sluice and caught below, delivering 

 it into the pipe or spout feeding the rearing-boxes. On next page 

 is a diagram of the tray (Figs. 99, 100). 



