1902 Encyclopedia > Clocks > The Westminster Clock

Clocks
(Part 11)




Clocks (cont.)

The Westminster Clock


It is unnecessary to repeat the account of the long dispute between the Government, the architect of the house of Parliament, the astronomer royal, Sir E. Beckett, and some of the London clockmakers, which ended in the employment of the late E.J. Dent and his successor F. Dent from the designs and under the superintendence of Sir E. Beckett, as the inscription on it records. The fullest account of these was given in the 4th and 5th editions of the Treatise on Clocks, and we shall now only describe its construction. Fig. 27 is a front elevation or section lengthwise of the clock. The frame is 16 feet long and 5 _ wide, and it rests on two iron plates lying on the tops of the walls of the shaft near the middle of the tower, down which the weights descend. That wall reaches up to the bell chamber, and those iron plates are built right through it, and so is the great cock which carries the pendulum. The clockroom is 28 feet x 19, the remaining 9 of the square being occupied by the staircase and an air-shaft for ventilating the whole building.

The going part of the clock, however, not requiring such a long barrel as the striking parts, which have steel wire ropes ·55 inch thick, is shorter than they are, and is carried by an intermediate bar or frame bolted to the cross bars of the principal frame. The back of them is about 2 _ feet from the wall, to leave room for a man behind, and the pendulum cock is so made as to let his head come within it in order to look square at the escapement. The escapement is the double three legs (fig. 13), and the length of the teeth or legs is 6 inches. The drawing represents the wheels (except the beveled wheels leading off to the dials) as mere circles to prevent confusion. The numbers of teeth and the time of revolution of the principal ones are inserted and require no further notice. Their size can be taken form the scale; the great wheels of the striking parts are 2 _ and of the going part 2 inches thick, and all the wheels are of cast-iron except the smaller ones of the escapement, which are brass but are painted like the iron ones.

The maintaining power for keeping the clock going while winding is peculiar and probably unique. None of those already described could have kept in gear long enough, maintaining sufficient force all the time, as that part takes 10 minutes to wind, even if the man does not loiter over it. This is managed without a single extra wheel beyond the ordinary winding pinion of large clocks. The winding wheel on the end of the barrel is close to the great wheel, and you see the pinion with the winding arbor in the oblique piece of the front frame of the clock. Consequently that arbor is about 6 feet long, and a little movement of its back end makes no material obliquity in the two bushes; i.e., it may go a little out of parallel with all the other arbors in the clock without any impediment to its action. Its back pivot is carried, not in a fixed bush, but in the lower end of a bar a little longer than the great wheel’s radius, hanging form the back of the great arbor; and that bar has a spring click upon it which takes into ratchet teeth cast on the back of the great wheel. When the great wheel is turning, and you are not winding, the ratchets pass the click as usual, but as soon as you begin to wind the back end of the winding arbor would rise but for the click catching those teeth, and so the great wheel itself become the fulcrum for winding for the time. After the winding has gone a few minutes along tooth projecting from the back of the arbor catches against a stop, because that end of the hanging bar and pinion have all risen a little with the motion of the great wheel. Then the man is obliged to turn the handle back a little, which lets down the pinion, &c., and the click takes up some lower teeth; and so if the chooses to loiter an hour over the winding he can do no harm. The winding pinion "pumps" into gear and out again as usual. The going part will go 8 _ days, to provide for the possible forgetting of a day in winding. The weight is about 160 _; but only one-14th of the whole force of that weight is requisite to drive the pendulum, as was found by trial; the rest goes in overcoming the friction of all the machinery, including a ton and a half of hands and counterpoises, and in providing force enough to drive them through al weathers, except heavy snows, which occasionally accumulate thick enough on several minute hands at once, on the left side of the dials, to stop the clock, those hands being 11 feet long. For the dials are 22 _ feet in diameter, or contain 400 square feet each, and there are very few rooms where such a dial could be painted on the floor. They are made of iron framing filled in with opal glass. Each minute is 14 inches wide. The only larger dial in the world is in Mechlin church, which is 40 feet wide; but it has no minute hand, which makes an enormous difference in the force required in the clock. They are completely walled off from the clock-room by a passage all round and there are a multitude of gas lights behind them, which are lighted by hand, though provision was originally made in the clock for doing is immaterial, and were left as they were made of gun metal under the architect’s direction; bit it was impossible to have minute hands of that construction and weight without injury to the clock, and so they were removed by Sir E. Beckett, and other made of copper tubes, with a section composed of two circular arcs put together, and are consequently very stiff, while weighing only 28 _. The great weight is in the wheels, tubes, and counterpoises. The minute hands are partly counterpoised outside, making their total length 14 feet, to relieve the strain upon their arbors. They all run on friction wheels inbedded in the larger tubes 5 1/2 inches wide, which carry the hour hands which themselves run on fixed wheels.

Then the man is obliged to turn the handle back little, which lets down the pinion, &c., and the click takes up some lower teeth; and so if he chooses to loiter an hour over the winding he can do no harm. The winding pinion "pumps" into gear and out again as usual. The going part will go 8 _ days, to provide for the possible forgetting of a day in winding. The weight is about 160 _; but only one-14th of the whole force of that weight is requisite to drive the pendulum, as was found by trial; the rest goes in overcoming the friction of all the machinery, including a ton and a half of hands and counterpoises, and in providing force enough to drive them through all weathers, except heavy snows, which occasionally accumulate thick enough on several minute hands at once, on the left side of the dials, to stop the clock, those hands being 11 feet long. For the dials are 22 _ feet in diameter, or contain 400 square feet each, and there are very few rooms where such a dial could be painted on the floor. They are made of iron framing filled in with opal glass. Each minute is 14 inches wide. The only larger dial in the world is in Mechlin church, which is 40 feet wide; but it has no minute hand, which makes an enormous difference in the force required in the clock. They are completely walled off from the clock-room by a passage all round, and there are a multitude of gas lights behind them, which are lighted by hand, though provision was originally made in the clock for doing it automatically. The hour hands go so slow that their weight is immaterial, and were left as they were made of gun metal under the architect’s direction; but it was impossible to have minute hands of that construction and weight without injury to the clock, and so they were removed by Sir E. Beckett, and others made of copper tubes, with a section composed of two circular arcs put together, and are consequently very stiff, while weighing only 28 _. The great weight is in the wheels, tubes, and counterpoises. The minute hands are partly counterpoised outside, making their total length 14 feet, to relieve the strain upon their arbor. They all run on friction wheels imbedded in the larger tubes 5 _ inches wide, which carry the hour hands, which themselves run on fixed friction wheels.





There is nothing peculiar in the quarter striking part except its size, and perhaps in the barrel turning in an hour and a half, i.e., in three repetitions of the five chimes already described. The cams are of wrought iron with hard steel faces. Each bell has two hammers, which enables the cams to be longer and the pressure on them less. The hour-striking wheel has ten cams 2 _ in. wide cast on it; but those cams have solid steel faces screwed on them. All this work was made for a hammer of 7 cwt., lifted 13 inches from the bell, i.e., about 9 inches of vertical lift. The hammer was reduced to 4 cwt. After the partial cracking of the bell. The rod from the lever to the hammer is made of the same wire rope as the weight ropes, and t eh result is that there is no noise in the room while the clock is striking. The lever is 5 feet 4 inches long, and strikes against the buffer spring shown in the drawing, to prevent concussion on the clock-frame, of which you cannot fell the least. The quarter hammer levers have smaller springs for the same purpose, and the stops of the striking part are also set on springs instead of rigid as usual. The files, for which there was not room in drawing, are near the top of the room and are each 2 feet 4 inches square. They make a considerable wind in the room when revolving. The only noise made in striking is their running on over their ratchets when the striking stops. Each striking weight is a ton and a half—or was before the great hammer was reduced. They take 5 hours to wind up, and it has to be done twice a week, which was thought better than making the parts larger and the teeth more numerous and the weights twice as much, to go a week, and of course the winding must have twice as long, as it was adapted to what a man can do continuously for some hours. Consequently it was necessary to contrive something to stop man winding just before each time of striking. And that is done by a lever being tipped over the snail at that time, which at once stops the winding. When the striking is done the man can put the lever up again and go on. The loose winding wheels are not pumped in and out of gear as usual, being too heavy, but one end of the arbor is pushed into gear by an eccentric bush turned by the oblique handle or lever which you see near the upper corner of each striking part, and they can be turned in a moment. They are held in their place for gear by a spring catch to prevent any risk of slipping out. Moreover the ropes themselves stop the winding when the weights came to the top, pretty much as they do in a spring clock or a watch, though not exactly.

The mode of letting off the hour striking is peculiar, with a view to the first blow of the our being exactly at the 60th second of the 60th minute. It was found that this could not be depended on to a single beat of the pendulum, and probably it never can in any clock, by a more snail turning in an hour, unless it was of a very inconvenient size. Therefore the common snail only lets it off partially, and the striking stop still rests against a lever which is not dropped but tipped up with a slight blow by another weighted lever resting on a snail on the 15-minute wheel, which moves more exactly with the escapement than the common snail lover in the train. The hammer is left on the lift, ready to fall, and it always does fall within half a second after the last beat of the pendulum at the hour. This is shown in fig. 28, where BE is the spring stop noticed above, and P the ordinary first stop on the long lifting lever PQ (which goes on far beyond the reach of the figure to the hour snail). The second or warning stop is CD, and BAS is the extra lever with its heavy end at S on the 15-minute snail. When that falls the end B tips up CD with certainty by the blow, and then the striking is free. The first, second, and third quarters begin at the proper times; but the fourth quarter chimes begin about 20 seconds before the hour.

The clock reports its own rate to Greenwich Observatory by galvanic action twice a day, i.e., an electric circuits is made and broken by the pressing together of certain springs at two given hours, and in this way the rate of the clock is ascertained and recorded, and the general results published by the astronomer royal in his annual report. This has been for some years so remarkably uniform, that the error has only reached 3 seconds on 3 per cent. of the days in the year, and is generally under two. He has also reported that "the rate of the clock is certain to much less than a second a week"—subject to abnormal disturbances by thunder storms which sometimes amount to seven or eight seconds, and other casualties, which are easily distinguishable from the spontaneous variations. The original stipulation in 1845 was that the rate should not very more than a second a day—not a week; and this was pronounced impossible by Mr Vulliamy and the London Company of Clockmakers, and it is true that up to that time no such rate has ever been attained by any large clock. In 1851 it was by the abovementioned clock, now at King’s Cross Station, by means of the train remontoire, which was then intended to be used at Westminster, but was superseded by the gravity escapement.

The great hour bell, of the note E, weights 13 _ tons and is 9 feet diameter and 9 inches thick. The quarter bells weigh respectively 78, 33 1/2 , 26, and 21 cwt.; with diameters 6 feet, 4 1/2 , 4, and 3 feet 9 inches, and notes B, E, F sh. And G sh. The hammers are on double levers embracing the bells, and turning on pivots projecting from the iron collars which carry the mushrooms shaped tops of the bells, cost nearly £6000, and the clock £4080. The bell frame, which is of wrought iron plates, and the dials and hands, all provided by the architect, cost £11,934—a curious case of the accessories costing more than the principals. (E. B.)



The above article was written by Edmund Beckett, the Right Hon. Lord Grimthorpe, K.C., LL.D.; author of works on clocks, architecture and astronomy.







Read the rest of this article:
Clocks - Table of Contents





Search the Encyclopedia:



About this EncyclopediaTop ContributorsAll ContributorsToday in History
Sitemaps
Terms of UsePrivacyContact Us



© 2005-17 1902 Encyclopedia. All Rights Reserved.

This website is the free online Encyclopedia Britannica (9th Edition and 10th Edition) with added expert translations and commentaries