Geoscience Reference
In-Depth Information
People
Christiaan Huygens (1629-1695)
Born in The Hague in the Netherlands, Huygens studied in Leiden and Breda. His father
corresponded with Marin Mersenne and his son eventually joined in the correspondence;
Mersenne challenged Huygens with mathematical problems and stimulated his interest.
Huygens took up telescope-making and with one of them discovered the large satellite of
Saturn, Titan, and the true nature of the planet's ring system. Although his health was never
robust, he was widely traveled and visited Copenhagen, London and Paris. In 1666 he
joined the Academy of Sciences at its foundation helping to set it up along the lines of the
Royal Society of London, of which he became a fellow in 1663. He kept his association
with the Academy, even when France was at war with the Netherlands during the War of
the Spanish Succession, until 1681. In 1689 he met Isaac Newton in London and in 1698
published (posthumously) one of the first topics about the possibility of extraterrestrial life
(over the next 15 years it was translated into English, French, German and Russian, a rapidity
that would be remarkable even today). His association with Gian Domenico Cassini is
remembered in the naming of the HUYGENS space probe that was landed on Saturn's
moon, Titan in January 2005, carried there by the CASSINI spacecraft.
Other scientists were working to measure the length of the seconds pendulum,
but different observers reported remarkably different values. One cause of the variation
in the length of the seconds pendulum was the temperature of the clock. The rate
of a pendulum depends on its length, therefore a given pendulum changes its beat
as a change of temperature causes its length to alter. The temperature rises, the
metal of the pendulum wire or rod expands, the pendulum length increases, and the
pendulum oscillates slower.
People
Marin Mersenne (1588-1648)
Marin Mersenne was a member of the order of the Minims who taught philosophy in
Nevers and moved to Paris in 1619. A mathematician, he is known particularly for his
discovery of the
Mersenne Prime Numbers
. Prime numbers are numbers that cannot be
subdivided into factors other than themselves and 1. Mersenne observed that a surprising
number of prime numbers are of the form 2
n
- 1. 3 is prime (it can only be factored as 3×1)
and it can be written 2
2
- 1. 7 is prime (7×1) and can be written 2
3
- 1. 31 is prime and can
be written 2
5
- 1. And so on. There are 44 Mersenne prime numbers known (as of 2008).
2
32,582,657
-1 is the largest, discovered September 2006. It has over 9 million decimal digits
and is tantalizingly close to winning the reward of $100,000 that has been offered for the
first prime number discovered with over 10 million digits.
Mersenne is also famous for his position at the center of a network of scientific discussion.
His cell in the monastery of the Minims de l'Annonciade near the Place Royale (the
present-day Place des Voges, the oldest square that survives in Paris), was a meeting place
for scientists and mathematicians like Fermat, Pascal, Gassendi, and others. These meet-
ings and people developed into the Academy of Sciences when it was founded by Colbert.
After Marsenne's death, letters were found in his cell from 78 scientists; he disseminated
results from one to the other in a web of correspondence that was the precursor of today's
scientific journals and preprint archives on the Internet.
Huygens did not believe in this imperfection of his clock. Describing the pendulum
clock in his topic
Horologium
(1658), Huygens referenced the Belgian astronomer
Godefroy Wendelin as observing that a pendulum clock beat faster in winter than
in summer. Huygens dismissed the observation as a mistake by Wendelin in cali-
brating the pendulum clock against hourglasses and sundials- they were too inac-
curate to make the comparison, said Huygens. Even as late as 1690, Huygens could
