Geoscience Reference
In-Depth Information
THE CONCEPT OF THE pendulum clock was due to Galileo. According to his
first biographer Vincenzo Viviani, while a student at the University of Pisa Galileo
began his study of pendulums after watching a suspended lamp swing back and
forth in the cathedral (presumably during a boring sermon.) He timed the period of
the swing with his pulse beats, beginning serious investigations in 1602 and discov-
ering that the period of a pendulum's swing is independent of its amplitude - in
other words, the time that the pendulum takes to traverse the arc of the swing is
always the same no matter how long the arc is. The isochronism of the pendulum
meant that it had an immediate application as a timepiece, and in 1603 a friend of
Galileo's, a physician in Venice named Santorio Santorio, began using a short
pendulum, which he called “pulsilogium,” to measure the pulse of patients. It was
nearly 40 years later that Galileo realized how the pendulum could be used to
improve a mechanical clock.
Mechanical clocks, using a heavy weight or a spring to provide power, had
replaced hour-glasses or water clocks (which measured time through the regular
flow of sand or drip of water). They worked by using an escapement, a lever that
pivoted and meshed with a toothed wheel at certain intervals. They were not very
accurate, though. They could lose or gain approximately 15 minutes per day. In
1641, at the age of 77 and completely blind, Galileo realized that a pendulum could
be connected to the escapement to regulate it. In 1658 in his biography of Galileo
Viviani described what happened as follows:
One day in 1641, while I was living with him at his villa in Arcetri, I remember that the idea
occurred to him that the pendulum could be adapted to clocks with weights or springs, serving
in place of the usual tempo, he hoping that the very even and natural motions of the pendulum
would correct all the defects in the art of clocks. But because his being deprived of sight
prevented his making drawings and models to the desired effect, and his son Vincenzio coming
one day from Florence to Arcetri, Galileo told him his idea and several discussions followed.
Finally they decided on a scheme … to be put in practice to learn the fact of those difficulties
in machines which are usually not foreseen in simple theorizing.
Galileo never made the pendulum clock that he had conceived, and it was
Christiaan Huygens who first invented the pendulum clock in about 1656. He patented
it in Holland, but his patent application in Italy was refused on the grounds that he
had plagiarized Galileo. His patent application in France was also refused three
times on the more pragmatic grounds that the master clock-makers of Paris might
object. He published his work on the design and the science of pendulum clocks
(
Horologium Oscillatorum
) in 1665, finding that he could readily achieve an accuracy
of 10 to 15 seconds per day, an enormous advance over the mechanical clocks available
until that time.
Within a year of publishing
Horologium Oscillatorum,
Huygens was invited by
Colbert to become a member of the Paris Academy of Sciences. At the same time
he set about developing the design of the pendulum clock and investigating its
scientific potential and found as part of the regulation of the clocks it was neces-
sary to determine the length of the pendulum that gave a calibrated time scale- the
seconds pendulum, namely one whose swing takes one second from end to end
(two seconds for the period).
