244 KEPORT — 1875. 



carriage ; and on pulling any one of these cords the lip is drawn down and the tube 

 reversed. A small counterweight, in the form of a flag, attached to the tube bv an 

 arm, prevents its returning to its former position, and at the same time shows at a 

 distance which liolder has been reversed. 



The communicating cable is in the first instance coiled round a light drum or 

 reel ; it consists of two copper wires perfectly insulated, and further protected by a 

 stout waterproof sheath. At intervals corresponding to the length of a carriage 

 short branches are led from each of these wires and taken through the sealed top of 

 a small wooden tube about 4 inches long (denominated a " tipper "), whence they 

 terminate in twy adjacent platinum points. The tipper, which is solid at the other 

 end, also contains a small quantity of pure mercury. 



The two batteries and bells, one for the locomotive the other for the guard's van, 

 may either be fixed in their respective places, or mounted inside a reel provided 

 with the wire and tippers, in which latter case there are absolutely no electric con- 

 nexions whatever to make, the cable being paid out either way from the centre of 

 the train, the wire of the two reels being continuous. In the former case the cable 

 is connected to the locomotive battery, then paid out along the train, the surplus 

 wu-e on its reel being placed in the guard's van alongside the second battery. 



The tippers are normally in a more or less upright position, and the mercury in 

 each remains at the bottom away from the wires. On reversing the tipper the 

 mercury flows downwards upon the wii-es, and thus causes both bells to ring. 



_ After a passenger has once pulled over a tipper lie cannot replace it, and the red 

 disk or flag makes detection easy. 



If desired the cable forms a ready means of intercommunication between guard 

 and driver at all times. 



Should a train part from a broken coupling, the cable will necessarily break ; but 

 before doing so the two tippers adjacent to the break will have been reversed, thas 

 calling attention of both driver and guard. 



On the Bristol Port and Channel Dock at Avonmouth, near Bristol. 

 By James Bktinlees, C.E. 



The site of the dock is so chosen that the centre line of the lock passes through the 

 centre of the mouth of the Avon, or what is known as the Swashway entrance from 

 Kingroad. Between the Swashwav and the lock there will be a deep channel, or 

 approach, 450 yards long by 100 yards wide. The part immediately in front of the 

 dock has a bell-mouthed shape, the side diverging fi-om the centre line of the lock at 

 an angle, and forming a tidal basin of about two acres in area. The lock is 600 ft. 

 in length, 70 feet wide from cope to cope, and has a depth of water on the lower 

 sills of 41 ft. 6 in. at high water equinoctial spring-tides. The dock itself is 1400 

 ft. ^ong by 500 ft. wide, and has an area of 16 acres. It will have a depth of water 

 of 35 ft. at high water equinoctial sjjrings, 31 ft. 3 in. at ordinary springs, and 22 ft. 

 3 m. at ordinary high-water neaps. By locking vessels in and out at high water 

 of neap-tides 28 ft. of water can always be maintained in the dock. 



The formation of a dam in front of the works proved of considerable difl[iculty, 

 biit it was successfidly constructed ; and although the tide has reached to within 2 ft. 

 6 in. of its top, it has never shown any symptom of weakness. About 1,320,000 

 c ubic yards of earth have been excavated fi-om the dock-basin and entrance-lock. 

 The_ excavations for the foundations were made with the help of portable engines for 

 pulling up the earth at the rate of 100 cubic yards per day. A steam-lift piunp, 

 throwing up 20,000 gallons an hour, was emploved to keep the foundation trenches 

 clear of water. 



The construction of the lock is the most important and costly part of the works. 

 Ihe foundations are laid about 6 ft. under low water equinoctial springs, the level 

 of the sand varying only about 12 in. throughout the whole 600 of its length. 

 Above the sand a bed of rubble masonry 6 ft. thick and fi-om 100 ft. to 120 ft. wide 

 is laid, and on this foundation the inverts and walls are built. The lentjth between 

 the inner and outer cells is 454 ft. This length is divided by a pair of gates into 

 cock-chambers, the outer 204 ft., and the inner 250 ft. in length. The sliuce-wavs 

 tor falling and emptying the locks are formed in the interior of the side walls. They 



