40 



houses is situated within the works, the water supply 

 being obtained from a 2O-ft. plank pond, used in winter 

 as a settling tank, and whose feeder is supplied by a 

 lo-in. pipe from the main inlet works. These in their turn 

 are supplied by a sluice in a coffer-dam, and guarded by 

 a screen placed nearly parallel to the surface, formed of 

 perforated zinc in summer and of wooden slats inch 

 apart in winter. The wooden frame had been removed on 

 the 3rd of March, when the temperature fell suddenly to 

 12 Fah., and the thin ice floating down the surface of the 

 stream clogged the perforated zinc screen, and froze into 

 a solid mass, entirely stopping the supply of the works ; 

 the water in the hatching trays unfortunately had been 

 lowered two days before to increase the current so as to 

 keep the eggs cleaner during the spate. The water fell in 

 the boxes sufficiently to partially expose the eggs, these just 

 showing the coloured globules which precede the formation 

 of the red blood, and a thin film of ice formed on all the 

 eggs. A few hours afterwards the screen was relieved, and 

 the eggs thawed out by a gentle current of water. For a 

 week no bad symptoms were visible, then several thousand 

 turned white ; in a month it was evident that, although 

 few more eggs had actually died, most of them had made 

 no further progress, and the few which showed a distinctly 

 formed embryo only proved how thorough had been the 

 work of destruction : the ice had squeezed all vitality out 

 of my baby Trout. 



The stoppage of water by the screen being clogged with 

 thin ice is frequently an invisible danger. It cannot occur 

 when the stream is frozen entirely over, as the thin ice only 

 travels on the surface, and when it comes against the screen 

 is held there by the suction of the water in the same way in 

 which a leaf is (this, of course, must not be confounded with 



