These figures do not include 10 levers used in ground frames at the platform buffer ends.

Although the levers have been reduced in number the lever movements will not, of course, be reduced in the same proportion, as the same number of signals remain to be operated - approximately so at least - as before, only the dual controls being reduced in number and the route levers entirely dispensed with.

As the signalman in the new box will only be able to see a small proportion of the area he controls and the appliances he operates, he must be provided with apparatus to take the place of his loss of vision and all that goes with such loss.

To describe the functions of the various parts which go to make up the whole machine I shall use the analogy of a living organism: the signalman must therefore have :-

(a) Nerves . (Train describers).
These take the place of the block instruments and advise the signalman that a train awaits entry into his section.

(b) Eyes. (Track circuits).
To give the signalman visual repeat- indication of the presence, and situation of a train or trains in his section.

(c) Arms or Members. (Point motors and Electric Signal Lights}.
To handle the train on its predetermined route.

(d) A Brain. (Signal Frame).
To correlate the messages received from nerves and eyes and so move the arms or members to control the movements of trains.

The items enumerated are as follows:-

(a) NERVES, TRAIN DESCRIBERS.
This apparatus being somewhat extensive in its ramifications can only be described in brief outline.

Owing to the increased area or section under control from St. Enoch new box, when handling passenger traffic, the signalman will have at one and the same time, three successive trains running concurrently on the same lines of rails. Obviously under these conditions ordinary block working is out of the question, therefore, train describers take the place of the block instruments.

The describers consist of transmitting and receiving panels with the originating points of transmission in the Up direction at St. Johns and St. Enoch, and in the Down direction at Strathbungo Junction on the G.B. & K. Line, Bellahouston No. 1 on the Canal Line and Pollock Junction on the Main Line. In the Down direction, cabins situated intermediately between the originating transmission point and the receiving box re-transmit all train indications received. Early indication is therefore given to St. Enoch of all approaching traffic.

The receiving panels give an illuminated indication showing both description and origin of each train and also its position in the section "queue," i.e., whether first, second or third. The first train indication vanishes when the train reaches the clearing track circuit in the station area, the second train indication then takes the place of the first- train indication, the third train indication, the place of the second train indication and a fourth train can now he indicated forward in place of the previous third train. This alteration to the indicators is entirely automatic in action being operated by the passage of the trains over the various track circuits utilised to mark the clearing points. The St. Enoch receiving indications (down line trains) are further classified as "In Section" until such time as the Home Signals protecting Gorbals Junction points have been passed in the clear position and the necessary track circuit occupied ahead when the indications change over to the ''Arrival' column of the panel.

Push buttons are used for all transmission purposes and re-setting keys, cancellation keys and emergency transmit keys are provided to cover all classes of failure and altered transmission required for the expeditious working of traffic.

St. Enoch is also provided with an indicator which shows all transmitted train indications for the Up Lines so long as the trains concerned are under control of St. Enoch signals. Incorporated with this panel is a platform "ready to depart" indicator with illuminated stencilled figure indications, 1 to 12 ; this indicates when a train is ready to start and will be operated by the platform staff.

A special instrument is provided in St. John's to cover setting back, shunt forward and other permissive workings on the Saltmarket Lines.

(b) EYES. TRACK CIRCUITS.
A track circuit is a means whereby a portion or portions of the two running rails is insulated from the neighbouring lengths, then supplied with electrical energy—in this case 3 Volts A.C.—and becomes a constantly energised electrical circuit. Controlled by these electric circuits are locks on certain signals and point levers only energised (i.e. free) when the full voltage is available. If the two rails forming these circuits are connected as by a pair of wheels with their connecting axle a "shunting" effect is obtained and this allows the current to follow the line of least resistance via the wheels and axles instead of flowing through its normal circuit to free the electric lock or locks on the levers controlled i.e. whilst the current is being "shunted'' the levers controlled become locked.

We are therefore able, by means of' these track circuits to exercise control over the levers of the signal frame (or brain) and so prevent illegitimate use being made of the points or signals (arms or members).

Actually, of course, there is interposed between the wires from the track circuited portions of the rails and the lever locks instruments called relays. These are a form of circuit maker or breaker as the case may be amd their types and functions can he summarised as hereunder :—

TRACK LINE AND CABIN RELAYS. Used as wire economizers.

"STICK" RELAYS Used in connection with the sectional release route locking, changing of light signal indications to red through occupancy of the track circuit ahead, etc., etc.

TIME ELEMENT RELAYS Used to operate locks on signal and point levers for a limited period of time maximum 1 minute - once a specified track circuit has been occupied by the leading vehicle;

In all 160 separate track circuits are provided in the new St.Enoch area, these indicate fouling points, trains standing at signals, etc. They are also used in connection with (ho locking of signal and point levers, sectional release route locking. i.e. holding the route ahead with point levers in normal or reverse position—once the signal has been passed with its operating lever over: approach controls (to prevent a signal clearing until the leading vehicle is close to same, i.e. carrying out rules 10 and 13b): putting signals to danger after a train has passed : selecting calling-on indications and providing clearing points for cancelling train describer indications.

In addition. the track circuits usually provide the signalman with eyes in the form of an illuminated diagram of the lines which repeals the condition of the 160 track circuits. Track circuit clear-- no light shows on diagram : track circuit occupied—two red lights show for each track circuit occupied.

Embodied in this diagram is a train waiting indicator for Down Line trains standing at No. 200 signal (also Gorbals Station Down Home). This indicator is operated by the Signalman in Gorbals Station box and takes the place of a track circuit at that signal.*

It is by means of track circuiting that we are enabled to arrange the distance apart we can run and store trains on the same line of rails, this being done by the use of overlaps and overruns. The word overlap is used to describe a length of separately track circuited line, marking a given distance ahead of a signal the forward termination of which marks cessation of control on a rear signal or signals. Should this distance be marked by a track circuit extended from the rear of and past the signal, the arrangement is then called an overrun.

In this scheme there are both overlaps and overruns full-filling the same purpose and so arranged that we can. with the leading train at a standstill at a signal, ''close-up" successive trains to a minimum distance of 70 yards apart between head and tail. The minimum distance of these same trains whilst running concurrently must, of course, be a minimum distance apart of two signals plus the 70 yards overlap.

Where calling-on signals are provided, trains can be stored, buffer to buffer, but their closest concurrent running is subject to the conditions above described.

(c) ARMS OR MEMBERS.
POINTS
All points will be operated electrically by a 1/3rd H.P. 110 Volt D.C. Motor each motor being a self contained unit, complete with electric detector, proving the two switch blades and the facing bolt in the "in'' position. All point motor point slides are fitted with an electrically operated lock, preventing movement of the point motor when any of the protecting track circuits are occupied. This lock is in addition to and separate from that on the signal frame lever operating the points. 121 point motors have been provided for this scheme.

*Author's Note. — Future developments will entail removal of this indicator.

SIGNALS.
The running signals are 3 aspect colour light signals giving the indications double red or stop: yellow above a red, proceed with caution and be prepared to stop at the next signal; green, next signal showing either yellow or green.

You will note the double red, and yellow and red aspects. This is due to the provision of a red marker light carried from 2' 6" to 5' below the main red light. This subsidiary red light provides a distinctive reminder to the driver that he is in territory where multiple aspect signals are in use. The marker light also serves as an alternative danger signal in the event of the main red light failing. Further, by using it along with the yellow light all risk of a red being mistaken for a yellow is eliminated

Where multiple aspect signals lead into a manual block section no red marker light is provided and this gives indication to a driver that he is leaving multiple aspect territory and entering a manual block section.

Where permissive working is in force, as throughout the St. Enoch Yard area and Saltmarket triangle, calling-on signals are provided. These comprise a red and yellow light unit carried under the main running signal. The yellow lens is a small one and its indication is given along with the main red light above it.

As already explained one lever operates both running and calling-on indications the latter being selected when one or more of the track circuits is occupied between it and the next signal ahead.

Banner signals are provided as ground signals for shunting movements. Each banner signal is illuminated at night by two 15 watt lamps the switch for these being under control of the signalman.

The lamps used in the various light signals are as follows : Main running signals—12 watts.
Two aspect shunt signal— 4 pin lights, each 9 watts. Wrong line indication for do.—25 watts.

The main signal lights are clearly visible in sunshine up to about 1,000 yards and penetrate even the densest, fog thus disposing of the need for fogmen.

Where lack of headroom exists a "searchlight" pattern signal is used having in addition to the marker light only one other light. The three light indication in this case are given on a vane with coloured screens moving in front of the latter light. The automatic signals on No. 2. 3 and 4 platforms and Nos. 9, 10, 11 and 12 platforms rear starting signals are of this type.

Pulling a signal lover does not necessarily alter its indication from red. the change of colour indication being subject, to control from the track circuits ahead and/or the indication given by the next signal ahead, with in some cases a further proviso that an approach track circuit must, be occupied when the signal ahead is red or when the signal ahead is at red with points set for a crossing movement and certain track circuits occupied.

All multiple and 2 aspect signals have their "clear" indications changed to red immediately the complete train has passed clear of the signal and its approach track circuit. This prevents a. signal being put to danger before the engine of a propelling train has reached it, and when an indication is so changed to red it remains at red until the operating lever has been restored to normal and pulled a second time.

The positions of the various signals have been mostly determined by the permanent way lay-out, platform ends etc.

At diverging points where a single signal applies to all routes a route indicator has been provided beside the signal concerned and this indicates by either letter or number the route to be traversed.

Throughout St. Enoch Yard area, signals are provided for wrong-line movements and on the Down Lines these movements are permitted out on to the Clyde Bridge. To trap any train overrunning, catch points with a sand drag have been laid down immediately south of the Clyde Bridge, and in addition elevated "Limit of Shunt" signals have been provided to mark the termination of movements of this kind.

The total number of signals of each type is as follows:—