Читать книгу Things to be Remembered in Daily Life - John Timbs - Страница 13

When labour and when dulness, club in hand,

Like the two figures at St. Dunstan’s, stand,

Beating alternately, in measur’d time,

The clockwork tintinnabulum of rhyme,

Exact and regular the sounds will be,

But such mere quarter-strokes are not for me.

These figures and the clock were put up in 1671. Among those who were struck by their oddity was the third Marquis of Hertford, born in 1777: “When a child, and a good child, his nurse, to reward him, would take him to see the giants at St. Dunstan’s; and he used to say that when he grew to be a man he would buy those giants” (Cunningham’s Handbook of London). Many a child of rich parents may have used the same words; but in the present case the Marquis kept his word. When the old church of St. Dunstan was taken down, in 1830, Lord Hertford attended the second auction-sale of the materials, and purchased the clock, bells, and figures for 200l.; he had them placed at the entrance to the grounds of his villa in the Regent’s Park, thence called St. Dunstan’s Villa; and here the figures do duty to the present day.

These automata remind us of the Minute-Jacks in Shakspeare’s Timon of Athens, generally interpreted as Jacks of the Clock-house:

You fools of fortune, trencher friends, time’s flies,

Cap and knee slaves, vapours, and minute-jacks.

Still, the Minute-Jacks only struck hours and quarters; and the term is rather thought to mean “fellows that watch their minutes to make their advantage, time-servers.” There is no doubt that by the “Jack that keeps the stroke,” in Richard III., is meant the Jack of the Clock-house.^[15]

A much more noteworthy sight than the Fleet-street clock-figures is possessed by the Londoners of the present day in the Time-ball Signal upon the roof of the Electric Telegraph Office, No. 448 West Strand.

The signal consists of a zinc ball, 6 feet in diameter, supported by a rod, which passes down the centre of a column, and carries at the base a piston, which, in its descent, plunges into a cast-iron air-cylinder; the escape of the air being regulated so as at pleasure to check the momentum of the ball, and prevent concussion. The raising of the ball, half-mast high, takes place daily at 10 minutes to 1 o’clock; at 5 minutes to 1 it is raised to the full height; and at 1 precisely, and simultaneously with the fall of the Time-ball at Greenwich Observatory (by which navigators correct their chronometers), it is liberated by the galvanic current sent from the Observatory, through a wire laid for that purpose. The same galvanic current which liberates the Ball in the Strand moves a needle upon the transit-clock of the Observatory, the time occupied by the transition being about 1-3000th part of a second; and by the unloosing of the machinery which supports the ball, less than one-fifth part of a second. The true moment of one o’clock is therefore indicated by the first appearance of the line of light between the dark cross over the ball and the body of the ball itself. There is a similar Time-ball upon the roof of a clockmaker’s in Cornhill.

At Edinburgh, also, is a Time-ball connected with a Time-gun signal, consisting of a large iron cannon, in the Half-moon Battery, at the Castle; which cannon, having been duly loaded and primed some time between twelve and one o’clock, is fired off precisely at the latter hour by an electric influence from the corrected Mean-time of the Royal Observatory, at a distance of three-quarters of a mile; which, however, first passes to another clock close to the gun, and thus affords a short fraction of a second before one o’clock for the train of processes; so that the actual final flash of the exploding gun in the Castle occurs absolutely coincidently with the tick of the sixtieth second of the corrected mean-time clock in the Royal Observatory. The whole is well described by Professor Piazzi Smith, Astronomer-Royal for Scotland, in Good Words, 1862, part iv.

We now return to the details of the great London Clocks. Mr. Dent undertook the construction of the Royal Exchange Clock in 1843: it was required to be superior to any public clock in England, and to satisfy certain conditions proposed for the first time by the Astronomer-Royal, and such as could not be satisfied by any clock of the common construction. Mr. Dent had then no factory of his own for making large clocks, and he could not get the clock made for him; “but with the energy and genius by which that remarkable man raised himself from a tallow-chandler’s apprentice to the position of the first horologist in the world, he set up a factory for himself at a great expense, and made the clock there; and of this, the first turret-clock he had ever made, the Astronomer-Royal certified, in 1845, that it not only satisfied his conditions, but that Mr. Dent had made some judicious improvements upon his suggestions, and that he had no doubt it was the best public clock in the world.”^[16] It is true to a second of time, and has a compensation-pendulum.

The Westminster Palace Clock, designed by Mr. Denison, has four dials, each 22½ feet wide: they are not the largest in the world, being considerably less than the dial at Mechlin; but there is no other clock in the world which has to work four dials of such great width, especially a clock going 8½ days. St. Paul’s Clock has only two 17-feet dials, and is wound up every day, which makes a vast difference in the power and strength required. Each pair of hands weighs above 2 cwt.: they are made of gun-metal, instead of sheet-iron or copper. The hour-sockets are iron tubes, 5 inches in diameter; the dials are of cast-iron framework, filled with opal glass, and stand out 5 feet from the main walls.

The size of public dials is often very inadequate to their height, and the distance at which they are intended to be seen. They ought to be at least one foot in diameter for every ten feet of height above the ground, and in many cases more, whenever the dial will be seen far off. Now, the clock-dials of St. Pancras, Euston-square, are but 6½ feet in diameter, though at the height of 100 feet, and therefore are much too small.

The Clock, of silver-gilt, presented by Henry VIII. to Anne Boleyn on the morning of their marriage, is one of the earliest chamber-clocks in the kingdom: the case is richly chased and engraved, and on the weights are the initial letters of Henry and Anne, with true-lovers’ knots. This clock was purchased at the Strawberry Hill sale in the year 1842, for 110l., and is now in the collection of Queen Victoria.

We may here mention that the late Duke of Sussex possessed, at Kensington Palace, an invaluable collection of the early as well as the most perfect specimens of Time-keepers, among which was “Harrison’s first Clock, the forerunner of that invaluable machine, without which the compass itself would be but an imperfect guide to the mariner.”^[17]

John Harrison received for his improved chronometers, in 1749, the Copley Medal; and, thus encouraged by the Royal Society, and by the hope of sharing the reward of 20,000l. offered by Parliament for the discovery of the longitude, Harrison produced in 1758 a time-keeper, which was sent for trial on a voyage to Jamaica. After 161 days, the error of the instrument was only one minute five seconds, and the maker received from the nation 5000l. For other chronometers, subjected, with perfect success, to a trial in a voyage to Barbadoes, Harrison received 10,000l. more. Dr. Stukeley writes of this ingenious man: “I passed by Mr. Harrison’s house at Barrow, that excellent genius of clock-making, who bids fair for the golden prize for the discovery of the longitude. I saw his famous clock last winter at Mr. George Graham’s: the sweetness of its motion, the contrivances to take off friction, to defeat the lengthening and shortening of the pendulum through heat and cold, and to prevent the disturbance of motion by that of the ship, cannot be sufficiently admired.”—Ms. Journal.^[18]

An exact measure of time is of the utmost importance to many of the sciences. Horology is indispensable to astronomy, in which the variation even of two or three seconds is of the greatest consequence. By means of a clock the Danish astronomer, Roemer, was enabled to discover that the eclipses of Jupiter’s satellites took place a few seconds later than he had calculated, when the earth was in that part of its orbit the farthest from Jupiter. Speculating on the cause of this phenomenon, he calculated that light was not propagated instantaneously, but took time to reach us; and, from calculations founded on this theory, light has been discovered to dart through space with a velocity of about 192,000 miles in a second: thus, the light of the sun takes eight minutes to reach the earth.

Horology has also enabled us to discover that when the wind passes one mile per hour, it is scarcely perceptible; while at the rate of one hundred miles per hour it acquires sufficient force to tear up trees, and destroy the produce of the earth. And, without the aid of a seconds-clock, it would have been scarcely possible to ascertain that a cannon-ball flies at the rate of 600 feet in a second.

The use of Chronometers in geography and navigation is well known; since it is only necessary to ascertain the exact difference in time between two places, to determine their distance east or west of each other.

Graham applied the motion of a Clock showing sidereal time to make a telescope point in the direction of any particular star, even when before the horizon.

Alexander Cummins made a Clock for George III. which registered the height of the barometer during every day throughout the year. This was effected by a circular card, of about 2 feet in diameter, being made to turn round once in a year. The card was divided by radii lines into 365 divisions, the months and days of the month being marked round the edge, while the usual range of the barometer was indicated in inches and tenths by circular lines described from the centre. A pencil with a fine point pressed on the card by a spring, and, held by an upright rod floating on the mercury, faithfully marked the state of the barometer; the card, being carried forward by the clock, brought each day to the pencil. Wren proposed to have a clock constructed on a similar principle, to register the position and force of the wind; which idea has been adopted.

In the Armoury of George IV. was a model of a small cannon, with a clock attached to the lock in such a manner that the trigger could be discharged at any desired time by setting the clock as an alarum.

Breguet contrived a Clock to set a Watch to time. This clock is of the size of a chamber-clock, and has a fork and support on a top to carry the watch. When the clock strikes twelve, a piece of steel like a needle rises, and entering a hole in the rim of the watch-case, comes in contact with a piece which carries the minute-hand, and by pressure makes the hand of the watch correspond with that of the clock, provided the difference be not more than twenty minutes.

The same artist constructed for George IV. a Chronometer which had two pendulums, one making the machine show mean time, the other to make it act as a metronome by beating the time for music. This pendulum was merely a small ball attached to a slight chain carried round a pulley, on the centre of which was an index, which, when brought to any of the musical measures engraved on the scale, shortened or lengthened the chain, so as to cause the pendulum to perform its oscillations in the time required, and a hammer struck on a bell the beats contained in each bar; these would be silently struck by placing a piece of wood between the hammer and the bell; the musical time was also indicated by the seconds-hand of the clock.

A certain dynamical theory of chemistry has been propounded, founded upon precipitations and decompositions taking place in a definite space. Time forms, too, the very key by which alone we can be admitted to a proper view of the archives of the ancient world. Want of time for the due development of the geological periods, for a long season, hindered men’s conceptions upon this subject from taking a sharp, clear cast of thought. Linnæus constructed a Clock of Flora—a dial of flowers, each opening and shutting at an appointed time.^[19]

By a series of comparisons with Pendulums placed at the surface and the interior of the earth, the Astronomer-Royal has ascertained the variation of gravity in descending to the bottom of a deep mine, as the Harton coal-pit, near South Shields. By calculations from these experiments, he has found the mean density of the earth to be 6·566, the specific gravity of water being represented by unity. In other words, it has been ascertained by these experiments that if the earth’s mass possessed every where its average density, it would weigh, bulk for bulk, 6·566 times as much as water. The immediate result of the computations of the Astronomer-Royal is: supposing a clock adjusted to go true time at the top of the mine, it would gain 2¼ seconds per day at the bottom. Or it may be stated thus: that gravity is greater at the bottom of a mine than at the top by 1/19190th part.^[20]

The Electric Clock is an invention of our own time. An ordinary clock consists essentially of a series of wheels acting on each other, and carrying round, as they revolve, the hands which mark the seconds, minutes, and hours. The wheels are moved by the falling of a weight, or the unwinding of a spring; and the rate at which they revolve is determined by the length of a pendulum made to oscillate by the wheels. In electric or (as they should rather be called) electro-magnetic clocks, there are neither weights nor springs; so that they never run down, and never require to be wound up. To produce motion, electricity is employed alternately to make and remake an electro-magnet, or alternately to reverse the poles of a permanent magnet, which, by lifting up and letting fall, or attracting and repelling a lever, moves the wheels.

M. Bouilly endeavoured to show that character was much influenced by Time-keepers. He describes two young persons who were allowed to select Watches for themselves: one chose a plain watch, being told that its performance could be depended on; the other, attracted by the elegance of a case, decided upon one of inferior construction. The possessor of the good Watch became remarkable for punctuality; while the other, although always in a hurry, was never in time, and discovered that, next to being too late, there is nothing worse than being too early.

The choice of a good Watch is, however, a difficult matter: none but a good workman is capable of forming a correct opinion; and a Watch must be bad indeed for an inexperienced eye to detect the errors either of the principle or its construction; even a trial of a year or two is no proof, for wear seldom takes place within that time; and while a good Watch can but go well, a bad one, by chance, may occasionally do so.

A Watch must not only be well constructed, and on a good principle, but the brass must be hard, and the steel properly tempered. The several parts must be in exact proportion, and well finished, so as to continue in motion with the least possible wear. It must also be so made that, when taken to pieces, all its parts may be replaced as firmly as before.

A bad Watch is one in which no more attention has been paid to the proportion of the parts, or durability of the material, than was necessary to make it perform for a time: it is either the production of inefficient workmen, or of those who, being limited in price, are unable to give sufficient time to perfect the work. In some instances these Watches will go well for a time; but as they wear, from friction, they require frequent repair, which cannot be effectually done.

The most useful lesson is, that low price is not exactly another word for cheapness. If you wish to possess a good Watch, apply to a maker of known honesty and ability in the art he professes, and who, therefore, should be implicitly trusted.

It has been said, that “no man ever made a true circle, or a straight line, except by chance;” and the same may be said of any machine which measured time exactly; indeed, positive accuracy can never be attained until an unchangeable material is discovered, of which the works may be constructed. These practical instructions are by Mr. Adam Thomson.

How beautifully has Lord Herbert of Cherbury sung “to his Watch when he could not sleep:”

Uncessant minutes, whilst you move you tell

The time that tells our life, which though it run

Never so fast or far, your new begun

Short steps shall overtake: for though life well

May ’scape his own account, it shall not yours.

You are Death’s auditors, that both divide

And sum whate’er that life inspir’d endures,

Past a beginning; and through you we bide

The doom of fate, whose unrecall’d decree

You date, bring, execute; making what’s new,

Ill, and good, old; for as we die in you,

You die in time, time in eternity.

13. Archæologia, vol. xxxvii.

14. Cunningham’s Handbook, 2d edit. p. 386. If this inscription be correct, it negatives the claim of Huyghens to having first applied the pendulum to the clock, about 1657; although Justus Bergen, mechanician to the Emperor Rodolphus, who reigned from 1576 to 1612, is said to have attached one to a clock used by Tycho Brahe. Inigo Jones, the architect of St. Paul’s, having been in Italy during the time of Galileo, it is probable that he communicated what he heard of the pendulum to Harris. Huyghens, however, violently contested for the priority; while others claimed it for the younger Galileo, who, they asserted, had, at his father’s suggestion, applied the pendulum to a clock in Venice which was finished in 1649.—Adam Thomson’s Time and Timekeepers, pp. 67, 68.

15. Nares’s Glossary.

16. Denison on Clocks.

17. Adam Thomson.

18. There is an odd traditionary story told of a Watch at Somerset House. A little above the entrance-door to the Stamps and Taxes is a white watch-face,—of which it is told, that when the wall was being built, a workman had the misfortune to fall from the scaffolding, and was only saved from destruction by the ribbon of his watch, which caught in a piece of projecting work. In thankful remembrance of his wonderful preservation, he is said to have inserted his watch into the face of the wall. Such is the popular belief, and hundreds of persons go to Somerset House to see this fancied memento, and hear the above tale. But the watch-face was placed in its present position many years ago by the Royal Society, as a meridian mark for a portable transit instrument in one of the windows of the anteroom. Captain Smyth assisted in mounting the instrument, and perfectly recollects the watch-face placed against the opposite wall.

19. The Relations of Science, by J. M. Ashley.

20. Letter to James Mather, Esq., South Shields. See also Professor Airy’s Lecture, 1854. Baily approximately weighed the earth by another contrivance, described and illustrated in Things not generally Known, First Series, which see.