ANNUAL ADDRESS. XV. 
centre of the saw was 9’ radius. The concrete was deposited in 
caissons, the bottom of which formed the permanent grillage, the 
sides were removed after the concrete was set and used over again. 
The concrete was composed of one barrel of cement to six cubic 
feet of sand and twenty-four cubic feet of broken stone. 
An interesting case of cheap dredging occurs at Liverpool, 
which has been undertaken by Mr. A. G. Lyster to improve the 
entrance to the river Mersey, so that vessels coming from America 
may not be delayed in consequence of the insufficient depth of 
water over the bar. Formerly vessels could only enter during the 
period of about two anda half hours, about high water. The 
dredge used for this purpose is of exceptional dimensions, being 
320’ long by 46’ beam, and having a draught when fully loaded 
with 3,000 tons of sand of 163’. The suction pipes which are two 
in number, are placed in the forward part of the ship, and the 
suction pipe which is 45’ in diameter is trailed aft through a well 
on the centre line of the ship. At its upper end it is fitted with 
_ atrunnion joint at the point where it branches off to the sand 
pumps, and below that again with a universal joint. The pipe is 
long enough to enable the vessel to dredge to a depth of 47° 
measured from the surface of the water to the surface of the sand. 
The hoppers for the reception of the sand are eight in number, 
placed on each side of ‘the well referred to. Instead of the usual 
hopper doors for the discharge of the sand, a 4’ hole is constructed 
at the bottom of each hopper, which is covered by a cylindrical 
valve extending to the top of the hopper, where its diameter is 
Somewhat greater than at the lower end. The valve, which is 
cased in at the upper and lower ends, is connected by a sliding 
pipe with the discharge from the circulating pumps, and when 
lifted, which is done by a hydraulic ram and cylinder, the water 
is turned on and is discharged through holes on the lower periphery 
of the valve, thus breaking up the sand and forcing it out through 
the hole in the hopper. By this means 3,000 tons of sand can be 
discharged in ten minutes. The sand pumps can dredge about 
400 tons an hour, and the cost of dredging is 0°89d. per ton repre- 
