The sundial is the oldest known device for the measurement of time and the most ancient of scientific instruments. It is based on the fact that the shadow of an object will move from one side of the object to the other as the sun “moves” from east to west during the day.
The first device for indicating the time of day was probably the gnomon. It consisted of a vertical stick or pillar; the length of the shadow it cast gave an indication of the time of day.
Sumer becomes the world’s first civilization. (Sumer is an ancient region of southern Mesopotamia – which is now southeastern Iraq.)
Babylonians and Egyptians build obelisks (slender, tapering four-sided monuments). Their moving shadows formed a kind of sundial, enabling citizens to divide the day into two parts by indicating noon. They also showed the year’s longest and shortest days when the shadow at noon was the longest or shortest of the year. Later, marks around the base of the monument would show further time divisions.
More precise sundials are built in Egypt. The earliest known sundial still preserved is an Egyptian shadow clock of green schist dating from at least this period. It consists of a straight base with a raised crosspiece at one end. The base, on which is inscribed a scale of six time divisions, is placed in an east-west direction with the crosspiece at the east end in the morning and the west end in the afternoon. The shadow of the crosspiece on the base indicates the time.
The earliest description of a sundial comes from Berossus, a Babylonian priest and author. His sundial is a cubical block into which a half-sphere is cut. A small bead is fixed at the center. During the day the shadow of the bead moves in a circular arc, divided into twelve equal parts. Because the length of the day varies with the season, these hours likewise vary in length from season to season and are thus known as “temporary hours.” (“Equal hours” were decided upon about 1300 AD, when mechanical clocks were invented.)
The first sundial is set up in Rome. It has been captured from the Samnites.
The Greeks develop and construct complex sundials using their knowledge of geometry:
- Apollonius of Perga develops the hemicyclium by using a surface of conic section upon which the hour lines are inscribed; thus providing greater accuracy.
- Ptolemy uses the analemma, a device that enables shadows to be projected geometrically onto flat surfaces inclined at various angles to the horizontal.
The first sundial is constructed for the city of Rome designed by architect and engineer Marcus Vitruvius Pollio. He mentions many types of sundials, some of which are portable, in his great work De architectura.
The Tower of the Winds is constructed in Athens. It is octagonal in shape and contains eight sundials. Sundials facing various cardinal compass points were in use at least since then.
Birth of Christ
It is discovered that the shadow cast by a slanting object is a more accurate timekeeper than a shadow cast by a vertical object. If the shadow-casting object is parallel to the earth’s axis, the direction of its shadow at any given hour of the day is constant regardless of the season of the year.
The Greeks introduce trigonometry into mathematics, thus supplying the tool for plotting hour lines with simple arithmetic calculations instead of the more cumbersome geometric constructions. This method will be exploited by the Arabs and later by European sundial makers.
Ab û al-Hasan writes on the construction of hour lines on cylindrical, conical, and other surfaces and is credited with introducing equal hours, at least for astronomical purposes.
The first all-mechanical clock is made. It is a large iron-framed structure, driven by weights. The function of the first European clocks was not to indicate the time on a dial, but to drive dials that give astronomical indications, and to sound the hour. They are located in monasteries and public bell towers. The earliest surviving example, constructed in 1386, is in Salisbury Cathedral, England. Mechanical clocks utilize equal hours.
The great age of the European sundial. Sundials with equal hours gradually come into use.
Galileo designs a clock using a pendulum as the timekeeping element.
The first pendulum clock model is completed by Christian Huygens in Holland. The use of the pendulum improves the timekeeping of clocks so much that all new clocks incorporate it.
French general Lafayette wants to express his respect and admiration for his ally and friend General George Washington during the American revolution. He chooses as his gift a silver Explorer sundial.
Clocks and watches begin to replace sundials. They have the advantage of not requiring sunny skies. They are, however, often unreliable and depend upon sundials to set the true time.
Early 1800’s AD
Mechanical clocks become accurate enough and inexpensive enough to displace sundials as the timepiece of choice.
Because of the earth’s rotation, a town 20 or 30 miles east or west has it’s clock set slightly differently. Your noon arrived somewhat before that of your western neighbor but sometime after that of your eastern neighbor. This made little difference because a resident might never travel to either of his neighboring towns.
Railroads are the preferred method of travel. Railroads demand schedules and schedules require “true” time. Along a 100 mile stretch of tracks there might be 6 towns with 6 different town clocks all different from the others. Passengers need to know when the train will arrive and depart and railroaders need to know when to send the next train in order to avoid accidents.
A conference is held and an agreement reached to divide the United States of America into four time zones, each 15 degrees wide – Eastern, Central, Mountain and Pacific, and all stations in a time zone would carry the same time. In fact, train time which is rigorously held to by the railroads becomes the time that cities and citizens set their clocks by. The train whistle becomes the signal for setting clocks.
The founder of Accurate Sundials, LLC starts designing, building and testing many types of accurate sundials. He designs a computer program for each major type of sundial to make the 174 calculations which go into each custom design.
The knowledge gained by Accurate Sundials, LLC in 24 years of research, along with expert support in computer aided design and machine shop technology, results in the attractive offering of elegant and accurate solid brass, copper and aluminum sundials you will find in it’s catalog. They also offer build-it-yourself site-specific layouts and directions for educational experience and project enjoyment.
Check back often to see new and exciting accurate sundials added to the offering of Accurate Sundials, LLC.
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