rnott._

Why do clocks denote the progress of time?

Because they count the oscillations of a pendulum; and by that peculiar
property of the pendulum, that one vibration commences exactly where the
last terminates, no part of time is lost or gained in the juxtaposition (or
putting together) of the units so counted, so that the precise fractional
part of a day can be ascertained, which each such unit measures. The origin
of the pendulum is traced to Galileo's observation of a hanging lamp in a
church at Pisa continuing to vibrate long and with singular uniformity,
after any accidental cause of disturbance. Hence he was led to investigate
the laws of the phenomenon, and out of what, in some shape or other, had
been before men's eyes from the beginning of the world, his powerful genius
extracted the most important results. The invention of pendulum clocks took
place about the middle of the seventeenth century; and the honour of the
discovery is disputed between Galileo and Huygens. Becher contends for
Galileo, and states that one Trifler made the first pendulum clock at
Florence, under the direction of Galileo Galilei, and that a model of it
was sent to Holland. The Accademia del Cimento also expressly declared,
that the application of the pendulum to the movement of a clock, was first
proposed by Galileo, and put in practice by his son, Vincenzo Galileo, in
1649. Huygens, however, contests the priority, and made a pendulum clock
before 1658; and he insists, that if ever Galileo had entertained such an
idea, he never brought it to perfection. Beckmann says the first pendulum
clock made in England, was constructed in the year 1662, by one Tromantil,
a Dutchman; but Grignon affirms that the first pendulum clock was made in
England, by Robert Harris, in 1641, and erected in Inigo Jones's church of
St. Paul, Covent-garden.

Why does the pendulum move faster in proportion as its journey is longer?

Because, in proportion as the arc described is more extended, the steeper
are its beginning and ending; and the more rapidly, therefore, the pendulum
falls down at first, sweeps along the intermediate space, and stops at
last.--_Arnott._

Why is it extremely difficult to ascertain the exact length of the
pendulum?

Because of the various expansion of metals, respecting which no two
pyrometers agree; the changeable nature of the atmosphere; the uncertainty
as to the true level of the sea; the extreme difficulty of measuring
accu