The Astronomy Book

91

See also: Gravitational theory 66–73 ■ The discovery of Ceres 94–99 ■
Investigating craters 212

URANUS TO NEPTUNE

Chladni published his findings in
a book in 1794, which set out his
main conclusions: that masses of
iron or stone fall from the sky; and
that friction in the atmosphere
causes them to heat up, creating
visible fireballs (“shooting stars”);
that the masses do not originate in
Earth’s atmosphere but far beyond
it; and that they are fragments of
bodies that never joined together
to make planets.
Chladni’s conclusions were
correct, but at the time he was
ridiculed—until some chance
rock-falls helped to change opinion.
The first of these took place within
two months of the publication
of Chladni’s book, when a large
fall of stones came down on the
outskirts of Siena, Italy. Analysis
of them showed they were very
different from anything found on
Earth. Then, in 1803, nearly 3,000
stones fell in fields around L’Aigle
in Normandy. French physicist

Jean-Baptiste Biot investigated

this fall. He concluded that

they could not have originated

anywhere nearby.

Solar system fragments

Thanks to Chladni’s work, scientists

know that shooting stars are lumps

of rock or metal from space heated

to glowing point as they pass

through the atmosphere. The object

that causes the glowing trail is

called a meteor. If any of it survives

to reach the ground, it is termed a

meteorite. Meteorites can originate

in the asteroid belt between Jupiter

and Mars, or they can be rocks

thrown up from Mars or the moon.

Many meteorites contain small

particles called chondrules, which

are thought to be material from the

asteroid belt that never formed into

larger bodies. These are some of

the oldest materials in the solar

system, and can tell scientists

much about its early composition. ■

These are

reliable reports.

The rocks show the effects

of extreme heating.

Rocks fall from space.

The rocks melted as

they fell through the

atmosphere.

Reports of rock-falls from the sky are all very similar.

Ernst Chladni

Ernst Chladni was born in

Saxony to a family of prominent

academics. Chladni’s father

disapproved of his son’s

interest in science and

insisted he study law and

philosophy. He obtained a

degree in these subjects from

the University of Leipzig in

1782. However, when his
      father died that year, he
      turned to physics.
      Initially, Chladni applied his
      physics knowledge to work in
      acoustics, which brought him
      renown. He identified the way
      rigid surfaces vibrate, and his
      observations were applied
      to the design of violins. His
      later work on meteorites drew
      less favorable attention from
      the scientists of the day, and
      might have vanished into
      obscurity had it not been for
      the popular writing of Jean-
      Baptist Biot, whose findings
      supported Chladni’s ideas.

Key works

1794 On the Origin of the

Iron Masses Found by 

Pallas and Others Similar

to it, and on Some Associated

Natural Phenomena

1819 Igneous Meteors and the

Substances that have Fallen

from them

The rocks do not

resemble local rocks.