52 TECHNOLOGY. 
perspective view of a chain of locks on the Rideau Canal, near Bytown in 
Canada. 7 
A lock consists of three divisions, viz. the upper entrance, called the 
head-bay ; the middle, called the chamber; and the lower entrance, 
called the tazl-bay. The difference in elevation between the bottom of the 
head-bay and the top of the tail-bay is called the d¢/¢, which varies accord- 
ing to circumstances from 5 to 15 feet. The highest single lift is in a lock 
at Bouzingen, near Ypern, in the Netherlands, amounting to 22 feet. The 
chamber is the narrowest part of the canal; it is made just large enough to 
admit of an easy entrance of the boat, and to leave some space for play 
during the commotion of the water while being lifted. It is formed by two 
solid walls of cut masonry, slightly battered towards the top; or if of wood 
the walls are built of heavy beams and planks fitted water-tight. Any 
excess in the size of the chamber above that required for the easy passage 
of the boat would only occasion loss of water and time. The head-bay as 
well as the tail-bay, being continuations of the main water-way, have 
of course the general depth of the canal; their form is usually that which 
we give in pl. 10, jigs. 1,3. a, and 36. The side-walls of the bays are called 
wing-walis, which are also battered, the batter or slope increasing from that 
of the chamber to that of the bank of the canal, where the wing-wall 
joins it. 
The lock gates are large and heavy gates consisting of two parts or leaves, 
each leaf turning upon its own hinges, and the two abutting against each 
other in the middle of the water-way, where they form an angle projecting 
against the head of water. There are always two gates to a lock, one at 
each end. They are usually made of wood, but latterly cast-iron gates 
have come into use and are greatly preferred. Those made of wood are 
carefully put together of heavy timber; the frame is usually composed of 
two upright and from four to eight horizontal pieces, which vary in thick- 
ness and depth according to the size of the gate and the head of water; 
these are mortised together, and covered on the side next to the head of 
water with durable two-inch planks, which are rabbet-jointed and caulked. 
The upright posts upon which the gate hinges are called heel-posts or 
guoins ; and the other uprights forming the edges of the two leaves of the 
gate are called the mztre posts. £1.10, figs. 22 and 23 a, are representations 
of different lock gates. Single leaves are also seen at A and B in jig. 20. 
The heel-post (fig. 26) is made to turn upon an iron gudgeon which fits into 
an iron plate below (jigs. 24 and 25); it is kept in its vertical position by 
means of two iron collars, which are fastened into the wall of the lock and 
in which it turns. The mitre-posts are so bevelled that when the gate is 
closed they abut against each other along the whole edge, and form a water- 
tight seam. The bottom of the gate is also bevelled and fits closely against 
the mitre sill, which forms the head of the head-wall and tail-wall running 
across each end of the chamber (a and 6, jig. 21). The water by its pres- 
sure produces a close contact of the bevelled faces, and is thus prevented 
from leaking through. 
The gates are opened in various ways: when they are very large, a chain 
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