S) 
the screen freezing up from insufficiency of water, which 
only occurs at a more advanced period of the frost); the 
stoppage, moreover, is temporary, for as soon as the tem- 
perature rises, or the stream freezes entirely across, the 
cause is removed, and the water soon clears the passage 
for itself, but in this lies the very essence of the danger, 
namely, that the water may have been off the works for a 
few hours, and the eggs exposed to frost, and in the morn- 
ing everything seems as usual, and the cause of the eggs 
dying, perhaps a week afterwards, entirely unsuspected. It 
is not advisable to place any hake or screen guarding the 
inlet perpendicular to the water, as leaves, &c., will collect 
in great quantities, and although fir branches laid in front 
generally prevent the water being entirely cut off, the 
amount of cleaning and watching is considerable, and a 
certain risk will always exist. 
A leaf screen made of perforated zinc laid nearly 
parallel with the surface of the water is probably the safest 
way of making a connection with an open river ; if pro- 
perly placed, any debris collecting on the screen, so soon 
as it begins to reduce the flow, is washed off by the upper 
current, and the supply after having passed through the 
zinc screen can be led into a small collecting well, and 
thence piped to the Hatching-house. 
The Hatchery itself should be substantially built on 
sound foundations, brick and concrete being probably the 
best materials to use; ventilation, light, and protection 
from frost are the principal objects in construction ; and 
above all things the drains must be sufficient and rat-proof. 
Keeping these points in view, the situation of the Hatchery 
should be governed by the water supply. The house also 
should be as large as possible, as very much better work 
can be done in a few central establishments than in many 
