Читать книгу Making Metal Clockworks for Home Machinists - Stan Bray - Страница 6

Before starting on constructional details of clockmaking, a word or two on the history of the subject may assist readers in an understanding of timekeeping in general. It is not only the human race that uses timekeeping methods; animals know when it is time to go to sleep or, if nocturnal, when to start searching for their food. Some plants and trees will close down flowers at night and open them when daylight appears. Of course, this has nothing to do with clocks as we have come to know them; they are reacting to light and dark and possibly also to changing seasons. No doubt the human race also started in this fashion, sleeping during darkness and active during the daylight. The clocks in use then were the sun and moon, not necessarily the most reliable sources, as, for various reasons, they are not always visible. Such primitive methods, while not exactly telling the time of day, did give reasonably accurate measurement of the seasons, and so had their uses.

It was not all left entirely to chance. Archaeology and ancient manuscripts tell us that the movement of the heavens has been observed for thousands of years and that this movement has been applied to timekeeping methods. The new moon appears every thirty days and the seasons repeat themselves every twelfth time it appears, which forms the basis of the year as we now record it. The equinoxes were well known and used for religious purposes, and stars and sun were used for early navigation, whether across sea or land.

During and prior to the Stone Age (from about 3.3 million years ago to 8000 BC), it is very doubtful if anything more accurate than this would be required. If the sun was at its highest point, then it was halfway through the day. Humans are never satisfied with basics and we can only speculate when it became desirable to be able to split time into smaller parts and exactly how it was done. It seems highly probable that a primitive sundial would be the first basic form of clock. Put a stick vertically in the ground, and when the shadow cast by that stick is at its shortest, it is midday. Who knows, perhaps it was a tree that first gave someone the idea that the shadow of the sun could be used to give an approximation of time.

Sundials did not remain as sticks in the ground, and we know stone columns were used in early times, metal pillars of varying shapes following them. This is not, however, a book about sundials but about clocks. The sundial subject is so vast that it would take a separate book to discuss it. What we do know is that sundials were in use around 200 BC, and a hundred years or so later a geared mechanical device was produced for navigational purposes at sea, which may or may not have been a primitive form of clock. In 600 BC, the Pope decreed that all religious institutions should have a sundial as a means of regulating the times for prayer, so the human race was really becoming more time conscious.

Not all the world’s population was Christian, and we must look at those countries that had not adopted the religion to see, where possible, how they sorted things out. It is known that the Chinese had the idea of using water. Although there was a number of variations on the theme, the basic principle was to first fill a container with water. A small hole in the bottom would allow it to run away, and by measuring the amount that had gone, it was possible to see how much time had passed and, if the container was marked with graduations, the time elapsed could be seen at a glance. This type of clock eventually became used all over the world, and various improvements made to the system, including attaching a dial, ensured that the water clock remained in use for hundreds of years.

Candles were also used as a measure of time. Once it could be established how much a candle burnt down in a particular period of time, it was a simple matter to mark the sides, showing how much time had elapsed since the candle was lit. King Alfred the Great (ca. 847–899) is credited with being the first person to use candles for timekeeping. It is still possible to buy candles marked in this way; nowadays they only have novelty value. An almost identical idea to the candle was to burn oil in a container with markings to record the time that had passed as the quantity of oil was reduced. For short time periods, there was also the sandglass, with which many of us will be familiar as an egg timer. The glass and quantity of sand had to be carefully matched to the time required, so the system was generally used only for specific purposes, because indicating intermediate time between filling and emptying the glass was not possible.

What of the religious orders that went to prayer night and day? Something was needed to tell them when it was time to go to the chapel. Even though the Pope had decreed that all religious institutes should have a sundial, this was of no use after dark or in much of the weather we have in Britain.

Various ingenious measuring devices that sounded alarms were devised; these included weights on a piece of string that was set fire to. After a period of time the flame burnt through the string and the weight would drop on a gong, telling the monks that it was prayer time. The idea was extended to include a number of weights strung to a frame. The strings were of different length and so burnt through at different times. In this way the gong could be sounded automatically at set intervals.

Nobody knows when the first mechanical clock came into being, or by whom or how it was invented. The oldest clock known of in Europe was at Salisbury Cathedral and is dated 1386. It is still in working order, and although no longer in the tower, it can be seen in the nave of the cathedral. It is quite an advanced clock that includes a mechanism for striking the hours, as well as one for telling the time. Even this is not the first known mechanical device: in 1090 Su Sung made a device in China that rang bells at given intervals in addition to driving automata, although it did not have a dial for timekeeping. Driving automata was popular with clockmakers, and one early example at Wells Cathedral, built in 1389, can still be seen working. It is a very elaborate affair, with knights jousting and all sorts of other movements at set times. We do know therefore that clocks have been in use for many hundreds of years, and although the construction of early ones appears to be quite crude, many were in fact sophisticated pieces of machinery. Early clocks were used for public purposes and were very large. Generally they would be housed in the tower of a church or cathedral.

There are records of clocks for domestic purposes as early as 1343 in France and England. The earliest surviving examples date from around the fifteenth century and are of iron construction, the mechanism being scaled down from the larger ones in public places. All these early clocks were weight driven, and exactly what date the pendulum replaced the folio control we cannot say. However, a claim is made that a clock was made with pendulum control in 1656. Spring drive is first heard of in 1450 and therefore predates the use of the pendulum. Regular improvements were made to the timekeeping mechanisms, including, in particular, the invention of new more reliable escapements, and in 1715 George Graham invented the deadbeat escapement, making clocks more reliable still.

It is quite amazing to think that modern mechanical clocks work on exactly the same principle as they did when George Graham invented his escapement. Materials have improved, with brass and steel taking over from iron, but otherwise there is little difference in the basic construction of any type of mechanical clock. Mass production was really the only big advancement from then on, but minor improvements to both clocks and watches continued.

In the twentieth century, clocks and watches saw advancements that would not have been thought possible, even at the start of the century. About sixty years or so ago, people first started to experiment with the use of electric clocks. Certainly, they were very primitive in comparison with what was to come later, but they had the advantage in that it was possible to synchronize several clocks together, which was ideal in a factory where many people were employed and all would be starting and stopping work at the same time. Prior to that, a bell or hooter was used, a system that in many places lasted until quite recent times.

Improvements in the manufacture of electric clocks were rapid until we reach the stage at which we are at today, where it is possible to buy a clock with a digital readout so that nobody even needs to know how to tell the time anymore. The modern electronic masterpieces can keep perfect time and are far more accurate than any except the most expensive mechanical clocks. Probably because of their efficiency they do not have the fascination of mechanical ones, which are still made today both commercially and by amateurs.

Many people buy mechanisms for these quartz clocks and make cases of various types to house them; it is a hobby on its own, in which large numbers of people are happy to indulge.

Before finishing with the history of clocks, it is interesting to think how time itself has changed. Until quite late in the nineteenth century, every town or district kept its own time. Communication between areas was very poor, with limited transportation, and it mattered not what time it was in a town forty or fifty miles away. With the coming of the railways all this changed. A person traveling from say London to Birmingham and then wanting to get a connection to somewhere else needed to know what time that connection would leave in relation to the train on which he or she would arrive. The railways therefore organized their own time, known as Railway Time, which was consistent right throughout the country. Gradually this was adopted throughout the country until everyone used the same. Now time is related directly to the Greenwich Meridian and known as Greenwich Mean Time. Other countries also take their time from the meridian, with allowances made for time zones. As a result, it is possible for anyone, anywhere, to know what time it is in any other part of the world.

The drawing represents an ancient water clock of about 200 BC, said to have been made by Ctesibius of Alexandria, who was a famous inventor. Water passes through the funnel into the reservoir, and in so doing raises the plunger. This incorporates a rack, and a hand with a gear wheel attached rotates to indicate the hours. The carefully regulated water supply is allowed to run for twenty-four hours and then the reservoir is emptied and the cycle repeated.