40 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



commuuicatiou Avith the water beneath the tray, though of course the 

 circulation of the water through the tray is not perfect. It is not, 

 therefore, deemed necessary to introduce any considerable devices for 

 filtering water which is naturally very pure, like lake aud spring water 

 when not subject to intermixture with surface water during rains; but 

 where it is necessary to use water subject to constant or occasional 

 turbiduess some method of filtering is indispensable. 



In the majority of cases at least a portion of the water supply is 

 obtained from an open brook, lake, or pond, aud measures must be taken 

 to get rid of the leaves and other coarse rubbish brought down by the 

 stream or conduit. A great deal of such material is encountered in a 

 stream at all seasons, but during fall and early winter it is especially 

 abundant, and to secure entire safety from a stoppage of the water, and 

 consequent loss, a screen on a generous scale must be provided. 



A description of the means adoi)ted at this station for providing a 

 temporary extra water service of several hundred gallons per minute, 

 taken from Craig Brook, will serve as an illustration : A tank or vat, 

 12 feet square and about 2 feet deep, is built in the bed of the brook 

 with a tight dam of stones, gravel, loam, and leaves (these to stop 

 small leaks) running ashore on either side, so that the entire volume of 

 the brook passes over the tank. The bottom aud sides are tight and 

 strong, and both bottom and top are inclined about 6 inches down the 

 stream. The cover is of spruce lumber sawed 1^ inches square, and 

 nailed on in the direction of the current, with interstices open half an 

 inch ; when in operation the water fills the tank and runs over the lower 

 edge, which is raised enough to maintain a depth of several inches over 

 nearly the whole tank. All leaves and other materials floating near the 

 surface of the water are carried over, together with most rubbish which 

 floats deep. At one of the lower corners of the tank, near the bottom, 

 is a gate about 15 inches square, which is hung by hinges on its upper 

 side. It opens inward, and is closed tightly by the pressure of the 

 water ; but it can be easily opened by pushing with a pole from without, 

 and then serves as a floodgate, whereby the tank may be thoroughly 

 cleaned out. 



At the other lower corner is a conduit, 6 by 9 inches, which takes 

 from this "leaf-screen" a supply of water not entirely free from rubbish, 

 but so nearly so that a filter of moderate capacity can cope with what 

 remains. A very useful adjunct would be a second horizontal screen 

 of similar coustruction, through which the water that has passed down- 

 ward through the first screen, as described, should next pass upward 

 through the second; the first screen would remove floating debris, the 

 second such as is heavier than water. 



The filter, situated about 70 feet from the leaf-screen, consists of a 

 wooden flume, 12 feet long and 1 feet deep, divided lengthwise into three 

 compartments, ot which the central contains fine gravel held in place 

 by a rack on either hand, of which the interstices are ^ inch wide and 

 IJ inches apart. The water from the leaf-screen is introduced into one 



