MIDDLETHIRD HATCHING-HOUSE. 107 



The sluice fitted near the upper end of the dam was at first 

 only intended for cleaning it out, but it was found in extraordin- 

 ary spates that the spout shot the water over the leaf-screen, and 

 although the conducting spout from the screen was so arranged 

 that no loss ever ensued, it was felt that the possible danger should 

 be obviated. This was done very simply by cutting the sluice- 

 boards, so that, whenever there was sufficient water passing the 

 V -spout on to the leaf-screen, the water in the dam stood level 

 with the top edge of the sluice-board. The sluice was the same 

 width as the mouth of the V -spout, but the clearance behind the 

 sluice was perfect, the fall being perpendicular, while the spout 

 lay at a very slight angle, and, moreover, from its shape, was neces- 

 sarily less than half this width a few inches in rear, the effect 

 being that, as the water rose, much more than half the flood- 

 water passed over the sluice. The object in the wide mouth of the 



-spout (Fig. 46) is to take all the water 

 required without raising the level in the 

 dam perceptibly, and thus ensure an even 

 head. The reason of raising the dam at 



1 1 , i j . v FIG. 46 scale A. 



ail is to stop gravel and dirt being 



carried on to the leaf-screen, as well as to gain a convenient height 

 for placing the screen. The mode of regulating dams by overflow 

 sluices is still common in parts of England, and was used by the 

 monks. It is a survival of a time when labour was almost valueless, 

 as, although admirably adapted for waste water, nothing could be 

 more primitive as a means of supply to a water-wheel. It is much 

 as if the supply were obtained by building a beavers' dam to collect 

 the water, and then removing stick by stick to obtain the power. 

 On next page is a drawing of the sluice (Figs. 47, 48). 



The next work was to excavate a ditch to take all the flood- 

 water passing the sluice ; this proved a hard task, the rock being 

 basalt, or, as it is popularly called, whinstone, and the formation 

 known to quarrymen as " teeth on edge." Of course a working 

 face was impossible, and the " quarrying " consisted in smashing 

 the " teeth" out with a sixty -pound hammer. This took me weeks, 

 and I often look back with amusement at brute force painfully 



