Measuring time
The "Portrait of young Man with a Skull" was painted by Bernadino
Licinio in 1510. At this time the first mechanical clocks were made, of
iron and wood. The clocks were driven by a weight and made
up of a gear system transforming the slow downward movenemt of the
weight to rotational energy pulsed via an "escapement" mechanism to a
balance wheel moving the hands of the clock. The balance wheel would
turn until it was drawn back by the escapement mechanism ready for a
new "tick".
These early timepieces were naturally unprecise to 60 min. a day,
sometimes ticking faster, sometimes slower, without a minutes hand and
not usable for astronomical or navigational measurements.
Hundred years later Galileo found that pendulums oscillate only
according to their length, independent of the mass of the bob, and
further 50 years later, in 1656, the Dutchman Christiaan Huygens
invented the pendulum clock hugely improving precision down to minutes
per day.
The pendulums now driving the hands of clocks had an almost natural
harmonic oscillation reflected in the increased precision. Rotating
balance wheels also soon was to be made more harmonic and precise
(again after an invention from Huygens) when equiped with a balance
spring pulling the balance wheel back instead of being drawn back by
the escapement.
After his invention of the pendulum clock Huygens found the perfect swing curve for a pendulum in a perfect clock should be part of an inverse cycloid rather than part of a circle. Experimentally it was found extremely difficult to construct such pendulums as they should have variable lenght, but long stiff pendulums with a short swing on a circular path was practically found to approximate Huygens perfect inverse cycloid path, and therfore isochrone and good timekeepers.
The strange cycloid curve has two qualities.If a skier wants to go down to a valley in the fastest way, he should look for an inverse cycloid track (brachistochrone quality). Beside being the fastest track to bring him down, the inverse cycloid path will bring him down in the same time independend of his starting point - it will take the same time to get to the valley starting from top or half or 3/4 down the curve (isochrone quality).
Skillfull clockmakers the next years refined the design of both the
balance spring watch and the pendulum clock so chronometers together
with a sextant in the 18'th century could be used at sea for
determining the latitude, and until the 1930's pendulum clocks was the
precise standard timekeepers in most countries - often locked in
airtight compartments in a vacuum.
Standard measure of distance could be defined from the seconds pendulum
(also called the Royal pendulum) used in many of the most precise
clocks. Each swing of these pendulums take one second, and the Danish
inch in 1821 was defined as 1/38 of the length of the seconds pendulum
at 45° latitude at the meridian of Skagen, at sea level and in vacuum.
A national standard long left, but still in use by carpenters in nordic
countries.