MIDDLETHIRD HATCHING-HOUSE. 113 



the screens was very simple. They were merely reversed, and 

 held for a few seconds below the side sluice from the V-spout, and 

 then replaced, care being taken not to move the lowest one 

 oftener than necessary, and always to remove the plug and clean 

 the bottom of the filter first. 



Frost never interfered with the working of the filter, but the 

 sheltered position and the comparatively high temperature of the 

 stream to a large extent account for this. I do not think such a 

 filter would be safe in many situations in Scotland ; in the south 

 of England, on the contrary, it would be safe, the depth enabling 

 it to stand a long and severe storm. 



A dike was next constructed from the lower end of the filter 

 to the hatching-house, and on it a covered spout of flooring was 

 laid, the soil being made up level with the dike on one side, and 

 rising perpendicularly from the old course of the stream. By this 

 means the spout was at once supported and protected from frost. 

 The old course of the stream received all the waste from the 

 filter, and also from the leaf-screen, and passed along the back of 

 the hatching-house, immediately below which it received the used 

 water of the boxes and trays. A new course in front of the house 

 carried the overflow from the dam. This new course required to 

 be carefully built with stone until past the hatching-house, as the 

 soil above the whinstone was very free and sandy. The two 

 courses joined a little below the house, and flowed on in the old 

 course (Fig. 57). 



FIG. 57 scale -fa. 

 SLATE FILTERS. 



The set of slate trays, one of which is described in the last 

 chapter, being ready early in summer, I had two slate filters made 



H 



