Saturday, July 30, 2005

For whom the bell tolls

A highlight of my recent trip to London was a trip to Parliament in order to visit the Westminster Clock.

Whilst not open to the public in the tourist sense, visits to the clock can be made very easily provided you are a British National- you simply book it via your Member of Parliament, free of charge.

There are three visits every weekday, at 10:30am, 11:30am and 2:30pm with a maximum of sixteen in the party and a minimum age of 11. We had arranged an 11:30 visit, which means being up the tower for Noon. I took my mum, with Karen & David going on to investigate another famous tower, the Monument commemorating the great fire of London. After going through the fairly intensive security (in a Portakabin outside St. Stephen’s entrance which has resulted in moving all of the unsightly security cabin out of the entrance hall) and passing an exhibition on Guy fawkes & the inevitable gift shop in Westminster Hall, we assembled near the Member’s entrance and met our tour guide. After checking that we were all up to the journey, we walked around the square and along the cloister towards the Clock Tower. In the distance we could see the tunnel leading to the escalators in Portcullis House, then as we neared we took a right turn into an archway and part way in we found ourselves standing outside an entrance to the left with three internal doors.

In order to get your bearings, the river runs North/South by Parliament and Westminster Bridge runs very close to the site boundary practically within spitting distance of the Clock Tower. We were standing facing the side opposite to the bridge, the Southern aspect. It wasn’t entirely obvious that we were at the base of the tower being under an archway, but as the flanking wall was about 40’ long and one of the inner doors was signwritten as being to the clock tower, it seemed that we were at the start of our marathon journey.

There isn’t a lift up the tower, access is via a staircase in the south-western corner of the tower, taking up maybe one ninth of the internal volume. The staircase is based on a square design with occasional landings and it spirals up in a clock-wise fashion. Pausing, it is possible to gaze up the central square core and see the handrail disappearing off into the heights. It is light and airy, being cream painted plaster with frequent vertical windows along the way. We did come quite quickly to a door numbered “1” in the north wall as well as some bricked up former windows, however we passed those and kept up the pace until reaching another door, this time in the east wall, also confusingly labelled “1”. This was to be our temporary resting place where we could leave coats & bags until our descent. The room was U shaped with only one door and we were advised that it also doubled as the prison room for errant members, although it hadn’t been used as such since 1880. It was U shaped due to a shaft down the centre of the tower used for the clock weights and which had also been used for hauling up the bells and mechanism in 1859. The main bell (the actual Big Ben) was wider than the shaft so it was hauled up sideways in a wooden frame. The prison room now had a number of displays about Parliament and the clock in particular, as well as a selection of artefacts including mechanical items from the mechanism, some of them broken or worn out. There was also a model of the escapement mechanism, called the Double three-legged gravity escapement.

The guide told us quite a bit about the history of the tower clock and bells, which can also be found here. He advised us that there were ten rooms in total up the tower and that we were now going to proceed up to clock-face level. We were only about a third of the way up so the next set of stairs would be a harder climb than the first set.

After a considerable trudge upwards passing various intermediate rooms (there tended to be a pair each landing then a full revolution without one so the room heights must have varied), we came to a doorway in the south-west corner of the staircase (i.e. to the outside!) after noticing that the outside walls had become noticeably thicker by the presence of two window alcoves deep enough to sleep in. We had arrived at dial level and after passing the backs of three identical clock faces we assembled at the South face for further briefing.

The clock faces (or more accurately, dials) are very big, being about 24' in diameter. They have 315 panes of frosted glass fitted in each one and there is an openable (but cable-tied) panel next to the number five (V) on each dial big enough to get your face through & presumably a brush to dislodge too much snow on the hands.

The back wall behind the face has a large number of discharge lamps, according to Philips there are 28 55W extremely long life discharge lamps per dial. They are rated at 60,000 hours and apparently the original lamps are still going strong from December 31st 1994. Before that, cold cathode fluorescent tubes were in use from the fifties, replacing electrification in 1906 and gas mantles before that. The wall still had a number of metal stays used for scrambling up in order to light the gas.

This was a rather overcast day so the hands and numerals were not too clear but had the sun been shining this would have been the best face to have visited. The rods driving the hands could be seen piercing the inner wall some 12'6" above us.

We then continued upwards, past room number 9 (which I correctly surmised would be the clock room), past a narrow door higher up and then finally the staircase opened up into the belfry. It was now a couple of minutes before twelve noon and we assembled on the north side facing the hammer of Big Ben. There are five bells up there, four for the quarter peal and the biggie for the big bong. The largest quarter bell had two hammers as the Westminster peal repeats the lowest note quickly at the end of the third bar and the beginning of the fourth bar for the full hour and a single hammer would not be able to actuate quickly enough.

There are actually five musical phrases played twice in the full peal across the hour, phrase 1 is for the quarter (a straight descent sequence), phrase 2 and 3 for the half hour, phrase 4, 5 and 1 again for the three quarter, then finally phrases 2,3,4 then 5 followed by the hour chime. It is apparently based on Handel's Messiah, was originally the Cambridge Chimes and has words:

All through this hour,
Lord be my guide,
And by thy power,
no foot shall slide.

It also goes by the name of the Westminster Quarters.

The Belfry can be recognised externally by seven vertical openings above the face. The bells are mounted onto a cast iron girder frame and the roof construction above leads to an upper gallery that includes an octagonal light fitting used to denote the House sitting at night. Access to this is by a wrought iron spiral stair and it was not available to us. What we did have to do was to go up onto a peculiar bridge structure that linked the north and south halves of the belfry. Big Ben cracked shortly after being installed and a substantial platform was subsequently built below it in order to retain the debris of any further damage. As it had a couple of girders blocking the walkway the bridge affair was presumably built to ease access. The Big Ben bell is fenced in and the smaller bells are somewhat out of reach above. All of the openings are meshed in, to keep pidgeons out and presumably visitors in. There is a small balcony beyond the openings with a very ornate stone balustrade capped in gold leafed orbs. It was also pointed out to us that the two thirds of the west tower not taken up with the stairwell were in fact a ventilation shaft from the original Charles Barry architectural design, although it didn't actually work until fires were lit at the base to draw the air. There was a large grid covering the shaft at belfry level, as well as a curious small shed-like structure at the far end of it towards the stairwell, possibly for a ventilation fan.

I was half-expecting all of us to be issued with ear defenders but we were told that we could put fingers in our ears if we chose, although it wasn't actually as ear shattering as we might think. Our warning of all hell breaking loose would be the rise of the hammer on the bell in the south east corner and the guide advised us that some steel wire ropes would be moving up and down to actuate the hammers so we should be wary of them, not because they were dangerous, but because they were greasy.

The full peal sounded and I found that it was bearable without fingers. After the 12th strike, I felt the supporting girders as suggested to feel the ongoing resonance of the thirteen and a half tonne Big Ben as the harmonics slowly died away. In the flesh, the bells sound pretty much like on the radio, exceot that Radio 4 doesn't make your teeth vibrate!

I took a quick look at the roping arrangement- the hauling rope was about 20mm diameter and it disappeared down into tubular glands about a foot above floor level. The one for the smallest quarter bell had a brass plate riveted to the top with the number 5 stamped onto it and one of the next nearest served the largest quarter bell and was numbered 4. The amount of rope travel must have been about 10" for the small bells and perhaps twice that for Big ben.

We then started downwards again and I was asked to lead the way down to room 9. The clock room itself was roughly about 25' long by about 18' deep and as you entered the room, the mechanism was on your left, seperated by a surrounding simple balustrade. It was lit by four elegant large wall fittings spaced out on the two long walls that incorporated the Parliament Portcullis into the design. The North wall had a long workbench with some inspection lights but the room was very clean and tidy to a high standard of finish as per the rest of the internal spaces.

The clock mechanism is spread out on a large rectangular frame supported by two brick piers either end which are an extension of the weight shaft walls. It has three distinct sets of mechanisms, known as trains. The centre part is known as the going train and is the bit that actually keeps time. A weighted drum provides the motive force to drive the hands and it is regulated by the escapement to the rear. A 14' pendulum swings with an interval of two seconds and every time the pendulum changes direction, it trips the escapement which also gives a slight push to the pendulum to keep it swinging. Fine tuning is by the means of coins on an accesible collor of the pendulum below and apparently it is the height of the coin that alters the centre of gravity, not the weight. An old penny has the effect of two fifths of a second every 24 hours. Every time the escapement spins, the minute hands turn one thirtieth of the distance between the minute segments on the dial, which by my reckoning must be just under half an inch. The hour hands are geared to revolve at one twelth the speed via planar gearing and the link to the hands is via an upright shaft from the clock that transfers the movement in all four directions from gearing supported by two substantial girders that run across the room.

Every fifteen minutes, the going train triggers the chiming train which is to the right of the frame. This is actually a replacement mechanism, as the original one went horribly wrong one night in 1976 and showered the room in gears and the drum went for a high speed wander round the room, ending up next to the bench in the corner. The air brake mechanism failed due to a sheared shaft and as a consequence the chime train simply span faster and faster whilst its weight plummeted to the bottom of the tower, landing on sandbags below.

At thirteen minutes past twelve, the air brake moved slightly, with a clunk and a slight spin on the ratchet. This was the warning to anyone working on the clock that it was now close to operating. Apparently, the horological term is that the clock has "warned". I positioned myself to the operating cams to see what would happen next.

To the right of the frame, five vertical steel wires rose to pierce through a row of tube lined openings in the roof. They were much smaller wires than the ones actuating the hammers, being no more than 6 mil. They also didn't actually move very far when operated, no more than about three inches. I would surmise then, that the floor above would have a complex pulley arrangement to distribute the ropes to the right places under the bells and introduce mechanical disadvantage, i.e. use the force in a negative ratio of 3 or 4 to 1 to get sufficient movement to move the hammers.

As the chiming train actuated, four of the five ropes operated in sequence from back to front, which relates to playing the four bells in descending order. I didn't have sufficient knowledge of the peal to work out beforehand how it would operate but another visit would make reading of the cams straight-forward. Unsurprisingly, the cams were shaped like sawblade teeth, to smoothly lift the hammer then let it fall under gravity for the strike. Whilst the mechanism was actuating, the air paddle above was spinning furiously and at continued to spin on the ratchet for severl seconds after the movement had stopped.

To the left of the frame was the striking train, used to operate the hours. We weren't to see this operate as it was now time to return back down to room one and collect our things. The guide pointed out two photos in the corner of the 1976 damage and I also had a quick look at the winding mechanism below which is motorised and winds the chiming and striking trains. The going train is wound by hand three times a week and takes about twenty minutes. Apparently it is designed as an eight day mechanism, however, the longer you leave it, the longer it takes to wind up!

After going round and round in squared circles for what seemed like an infeasibly long time, we reached our gallery room again, where we were given a brief guide to the visit and had a final chance to ask questions. I meant to ask what was in the other intermediate rooms on the way up but never got round to it.

It was a very fascinating hour which simply flew by, although the trek was rather arduous on the way up, especially up to dial level. The guide also threw in a number of other little snippets and anecdotes which showed that he certainly knew his stuff. If you get a chance, take it, they might not do it for ever once Health & Safety throw their oars in...

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