the length of the tropical year 1900. But like most measurements, the second definition
changed again in 1964, when it was assigned to be the equivalent of 9,192,631,770
cycles of radiation associated with a particular change in state of a cesium-133 atom.
Interestingly enough, by 1983 the second became the “definer” of the meter: Sci-
entists defined a meter as 1/299,792,458 the distance light travels in one second. This
was done because the distance light travels in one second was more accurate than the
former definition of the standard meter.
MATH AND CALENDARS IN HISTORY
What is the connectionbetween calendars and math?
A calendar is essentially a numbering system that represents a systematic way of orga-
nizing days into weeks, months, years, and millennia, especially in terms of a human
lifespan. It was the necessity to count, keep track of, and organize days, months, and
so on that gave rise to calendars, all of which also entails the knowledge of mathemat-
ics to make such calculations.
When were the first calendars invented?
Although the first crude types of calendars may have appeared some 30,000 years
ago—they were based on the movements of the Moon and indicated as marks on
bones—the Egyptians are given credit for having the first true calendars. Scientists
believe that around 4500 BCEthe Egyptians needed such a tool to keep track of the
Nile River’s flooding. From about 4236 BCE, the beginning of the year was chosen as 59
MATHEMATICS THROUGHOUT HISTORY
Where was the mechanical clock first invented?
I
t is thought that the first mechanical clock was invented in medieval Europe and
used most extensively by churches and monasteries (mainly to tell when to ring
the bells for church attendance). The clocks had an arrangement of gears and
wheels, which were all turned by attached weights. As gravity pulled on the weights,
the wheels would turn in a slow, regular manner; as the wheels turned, they were
also attached to a pointer, a way of marking the hours, but not yet minutes.The precursor to accurate time keeping came around 1500 with the advent
of the “spring-powered clock,” an invention by German locksmith Peter Henlein
(1480–1542). It still had problems, though, especially with the slowing down of
the clock as the spring unwound. But it became a favorite of the rich because of
its small size, easily fitting on a mantle or shelf.