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E in specially constructed chambers on one of the walls. : - The pumps, which are of the cen- trifugal type, 17 in. in diameter, are seated on a main drain at the bot- tom of the dock, which is continued over practically the whole length of each section. From the main-drain compartment pipes are led to each separate water-tight division of the dock. Each compartment is governed by its own separate valve, and the main inlet pipe and pump discharge pipe are governed by separate screw- - down valves, and in addition have each a non-return flap-valve on the outside. The compartment valves of each section of the dock are all op- erated from a valve-house placed on the top deck of each section, by means of the Westinghouse electro- pneumatic system, which is based on the principle of operating presses by compressed air and controlling the same from a distance by means of valves operated by an_ electro-mag- net. Each valve house is in tele- phonic communication with its re- spective engine room and also with the others when the dock is work- ing as a single unit. Pumping Equipment Each section of the dock is also provided with a direct-acting steam- pump, arranged to draw from the sea, and capable of providing a full stream of water for fire service or washing down vessels. These pumps are also connected to the main drain, so that they may be used as a drain- age service for completely emptying the compartments. Two. similar steam pumps are also fitted on the opposite wall of the dock. Steam heating is provided to pre- vent water in the compartments from freezing, and also for the mechanism that could be affected by frost. Each water tight compartment is provided with the Gardner & Ferguson indi- cating system, to show, in the valve house, the level of the water inside it. Similar gear is also provided for indicating the draught of water over the: keel blocks. The dock is pro- vided with eight steam capstans, four on each wall. The spindles of the capstans are carried down vertically to the level of the pontoon deck, where, in a small chamber in the wall at this level, cable lifters are fitted, so that the mooring cables may be hauled in or paid out when the dock is being moved about. Don- key boilers are provided on the wall remote from that in which the main boilers are fitted, to provide steam for the capstans and fire pumps fitted on that wall. On thé top deck of this wall a 3-ton electric traveling THE MARINE REVIEW gantry crane is fitted and arranged to traverse the whole length of the wall. At both ends of the combined dock a pair of flying gangways or swinging bridges are fitted, affording access from one wall to the other. Lighted by Electricity The dock will be lighted through- out the machinery compartments by means of electric lamps. The out- side lighting consists of bracket standards, each supporting a cluster of lamps. Box terminals are also fitted on the walls, from which lamp clusters can be taken by flexible leads for lighting any particular portion of the ship on the dock. Electric current will be supplied through cab- les from the shore. The dock is provided with the us- ual bollards and timber heads. Roll- er fenders are also fitted to protect the walls of the dock from an enter- ing steamer. Eight mechanical side shores, four on each wall, are pro- vided. These can be screwed in or out. by a standard fitted on the top deck. Keel blocks, side or docking keel blocks, and bilge blocks are pro- vided; the latter are arranged to be pulled in or out to suit the shape of the ship when she has taken the keel- blocks. The keel blocks are strong- ly made and closely spaced, to en- able them to take the weight of the heaviest and most modern ironclads. Ladders are fitted leading from the upper deck of the dock to the pon- toon deck, and also into the various compartments of the dock. Suitable hand. rails are fitted all round the top. deck. Ventilation by means of cowls and downcast pipes is arranged to each boiler and engine room, and also to the interior, of the' walls, A valve house large enough to contain the valve control table and the recording instruments is fitted on the top deck of each of the three sections; each valve house contains the apparatus necessary for controlling the valves of its own particular section. Electric Impulse Transmitter The Gardner-Ferguson electrical im- pulse transmitter is an instrument which has been devised with a view to obtaining regular and incremental electrical impulses from any motion in any position, and transmitting these impulses to any distance and there reproducing them synchronously, thus forming a history of a motion no mat- ter what it is. In essence the appara- tus consists of a spindle which is rotated, or oscillated, by the motion of which a record or observation at a distance is required. On this spindle September, 1912 are diametrically mounted one or more straight glass tubes which have a platinum wire fused into each of their closed ends, the tubes being partially filled with a special mixture, of which mercury is the principal component. On the requisite move- ment of the spindle the tube, or tubes, alternately pass through the horizontal plane, thereby causing the mercurial. mixture to flow in the tube and make a momentary electrical connection be- tween the end platinum wires and allowing an electrical impulse to flow. Collecting-rings are fixed on the spin- dle, and by means of these the im- puse current is conducted through, the external circuit to any distance which may be required. A simple mechan- ical device is attached to the spindle which prevents the tubes from stop- ping in the horizontal plane and thus causing a short-circuit. The instrument as described above is in its most siniple form, and jis suitable for a motion in one direction only, as, for example, from the in- dex or counter of any form of meter, or for the transmission of time from a master-clock to any number of synchronizing dials. If, on the other hand, the motion is reciprocating, regular or irregular, sometimes in one direction and sometimes in another, a simple commutator is fitted, which is operated by the same spindle which carries the glass tubes. An _ instru- ment with four glass tubes, and fitted with such a commutator for recipro- cating motion, is illustrated in Figs. 1 to 3. The arrangement of the com- mutator will be clearly understood from these figures. It is in essence a change-over switch, the moving part) of. which is carried by: an: arm which rides on the spindle, and the fixed part of which consists of two contacts carried by brackets from the bottom of the case, as shown. The moving arm is spring-controlled, so that as the spindle begins to move in the direction different from _ its previous motion, the arm springs across and makes contact with the epposite pair of contacts from that it was previously in connection with. The two contacts are connected up so that each sends the impulses in the transmission circuit in an opposite direction from the other. It is usual to make the transmission circuit with a single wire and an earth return, but a three-wire arrangement can be used if desired. It is obvious that the glass tubes form the only part of this ap- paratus which can be looked upon as of a special and more or less untried nature, but exhaustive tests have been made of its reliability. Tubes have been selected at random, and individu- ier ar