Ernst Florens Friedrich Chladni
Ernst Florens Friedrich Chladni
Ernst Chladni worked in the fields of acoustics (the study of sound waves) and meteoritics (the study of meteorites). At the time, these areas of science were still in their infancy, and Chladni is sometimes known as the "father" of both of these disciplines.
Ernst Chladni was born in Wittenberg, Germany, in 1756. His father was a lawyer, and Chladni was expected to become a lawyer as well. He studied law at the Universities of Leipzig and Wittenberg and received his degree in 1782. His father died soon after Chladni graduated, and as a result, he was free to devote himself to his true love—science. He gave up the practice of law and stayed on at the University of Wittenberg for several more years in order to study mathematics and science.
Chladni had an interest in music and soon began to investigate acoustics, the study of sound waves. Through his experiments, Chladni discovered an intriguing phenomenon. First, he covered a circular or rectangular metal plate with a thin layer of sand. Then he caused the plate to vibrate by rubbing it with a violin bow. The plate vibrated in a complex pattern, with certain lines on the plate remaining motionless. These lines are called nodal lines. The sand from the vibrating areas of the plates moved onto these lines, producing a pattern of sand that matched the pattern of vibration. He exhibited these patterns, now called Chladni figures, to a group of scientists in Paris in 1809. Today, Chladni figures are still used in demonstrations in high school and college physics classes.
Chladni also conducted experiments involving the speed of sound. In the seventeenth century, a French scientist named Pierre Gassendi (1592-1655) had measured the speed of sound in air. Chladni extended his work by developing a method of measuring the speed of sound in other gases. He did so by filling an organ pipe with a particular gas. Then he measured the pitch (the highness or lowness) of the sound produced by the pipe when it was played. By knowing the pitch, he could then calculate the speed of the sound in the gas.
Besides his contributions to the field of acoustics, Chladni also helped to establish the science of meteoritics—the study of meteorites. He was one of the first to propose that meteorites have an extraterrestrial origin. In Chladni's time, people had observed what appeared to be fireballs streaking across the sky. Various explanations were offered for these objects. For instance, some believed that they were an unusual form of lightning or somehow connected to the northern lights.
Scientists had also discovered unusual masses of stone or metal that seemed very different from the other rocks in the areas where they were found. (We now know that these stones are meteorites.) Again, various explanations were offered for the presence of these stones. Some believed they were formed from lightning strikes; others believed they came from volcanic explosions. However, scientists had not yet made the connection between fireballs and the unusual stones.
Chladni became interested in a 1,600-pound (726 kg) iron meteorite that had been found in Siberia. He was able to obtain samples of it, which he compared to other iron meteorites from around the world. Because of the similarities among them, Chladni concluded that they must all have the same source. Since they were all found far from iron deposits, he argued that these stones were not from Earth, but had fallen from space. He presented his findings in a book titled Concerning the Origin of the Mass of Iron Discovered by Pallas and Others similar to it, and Concerning a few Natural Phenomena Connected therewith in 1794.
Chladni also suggested that fireballs were caused when these stones entered Earth's atmosphere. The meteorites Chladni studied showed evidence of intense heating. He proposed that when a meteorite entered Earth's atmosphere at high speed, friction caused it to glow, producing a fireball that could be seen from the ground.
When his book was first published, other scientists rejected his ideas, in large part because they went against traditional scientific thinking. The year after Chladni's book was published, however, a large 56-pound (25 kg) meteorite fell into the English village of Wold Cottage. Several villagers observed its fall, and when scientists analyzed its composition, they found that it had similarities to other types of meteorites.
Just a few years later, the French town of L'Aigle was hit by about 3,000 meteorites. Jean Baptiste Biot (1774-1862) investigated this occurrence in 1803. He observed impact craters from the stones and tree branches that had been broken by the falls. He also interviewed villagers who had witnessed the event. When his findings were published, scientists began to accept Chladni's explanation of the extraterrestrial origin of meteorites.
The areas of science in which Chladni did his research—acoustics and meteoritics—were very new fields. Therefore, he had great difficulty finding a position as a science professor. As a result, he made a living by giving scientific lectures and performing on the euphonium, a musical instrument he had invented. It consisted of glass rods and steel bars that produced sounds when vibrated. (Chladni's euphonium was completely different from the modern euphonium, which is related to the tuba.) He died in 1827.
STACEY R. MURRAY
THE TRUTH IS OUT THERE
Before Chladni's research on meteorites, members of the general public (usually peasants) had reported seeing stones falling from the sky. Scientists tended to disregard these reports as being tall tales told by the ignorant. However, after Chladni's book was published and especially after Biot's dramatic report of the meteorites at l'Aigle, these falling stones became a new source of fascination for scientists and nonscientists alike.
For instance, when a shower of stones fell on Siena, Italy, local peasants sold many of them to eager English tourists. When demand for the meteorites became known, many ordinary stones were sold as "meteorites" to the unsuspecting. Meanwhile, Major Edward Topham, who owned the property on which the Wold Cottage meteor fell, was exhibiting the stone in a coffee shop. Visitors paid a small fee to look at the stone and to read the sworn testimony of those who had witnessed its fall. Articles began appearing in magazines about people who claimed to have seen falling stones, but had been afraid of coming forward previously for fear of public ridicule.
Some scientists were dismayed at these new meteorite enthusiasts, believing that the public was being led to accept nonsense. Speaking on this topic, the French scientist Eugène Patrin claimed that the "love of the marvelous is the most dangerous enemy of natural science." Within a decade, however, scientists generally accepted Chladni's ideas.
STACEY R. MURRAY