German Scientists:

Doppler, Röntgen, von Guericke

by Paul A. Schons

(Originally published by the Germanic American Institute in February, 1999)

In recent years we have heard a great deal about Doppler radar if we watch the local weather forecasts. But, although many appreciate the lovely colors the Doppler radar provides, fewer know that the "Doppler" in Doppler radar is the name of an Austrian scientist.

Christian Doppler was born in Salzburg, Austria on November 29, 1803. After his studies at the Polytechnical Institute in Vienna he became a professor of experimental physics at the University of Vienna. In his research Doppler became interested in the nature of light and sound. Through mathematical models and through observation he noted that the pitch of sound and the color of light are affected by the speed at which the sound source or the light source are moving in respect to the person hearing the sound or seeing the light. He published his observations in 1842 in "Über das farbige Licht der Doppelsterne" ("On the Colored Light of Double Stars").

The properties he observed have come to be known as the "Doppler effect." The most common demonstration of the Doppler effect is that when one stands by the side of a road and hears a car approaching the pitch of the sound seems to rise as the car approaches and fall again as the car moves away. The same is true of light. If a light source (such as a star) is moving, the color strikes the eye as more blue or red depending on if the star if moving toward the earth or away from it. (Much of the "Big Bang Theory" is concluded using the principles of the Doppler effect on light.)

Another German scientist whose work touches our daily lives is Wilhelm Röntgen. We appreciate his work each time our doctor is able to discover and cure our ills with the aid of an X-ray. X-rays were discovered by Röntgen, a physicist at the University of Würzburg. After observations which led him to conclude the existence of X-rays in nature, Röntgen went on to invent a camera which could take X-ray pictures. After success in taking X-ray pictures of a number of the things in his laboratory in Würzburg he went on to take the first X-ray picture of a human being. His first subject was the bones of his wife's hand. Röntgen announced his discoveries on November 8, 1895.

Röntgen was born in Remscheid, Germany (then Lennep, Prussia) on March 27, 1845. After his work at Würzburg he finished his career at the University of Munich where he died in 1923. Röntgen himself called the rays he had discovered X-rays, but today in German they are called Röntgenstrahlen (Röntgen rays). Röntgen's name is preserved in English too in the term roentgenology. The next time you are in Würzburg, if you would like to see the place where Röntgen invented X-rays, it is just a few blocks from the train station in the direction of the Main River.

Every time you encounter a vacuum cleaner you must thank a third German scientist, Otto von Guericke. It was von Guericke who did the world's pioneering work on vacuums and the nature of air pressure. (He did not invent the vacuum cleaner. That is simply an application of the principles he discovered.) In his researches von Guericke invented first the vacuum pump and with it was able to create a vacuum. With the vacuums he created, he was the first to learn that light travels through a vacuum but sound does not. In addition to his discovery of vacuums he was also to built the world's first electric generator in 1663.

Von Guericke was born on November 20, 1602 in Magdeburg, Germany. He had studied at the Universities of Leipzig and Jena. In addition to his scientific work he was the mayor of Magdeburg from 1646-1681. The vacuum was often discussed by philosophers of the times and it had been concluded that such a thing was logically impossible. Von Guericke demonstrated the reality of a vacuum and the power of air pressure in a famous experiment performed before the Emperor Ferdinand III in Regensburg in 1654. He placed two copper hemispheres together and after removing the air from inside with his new air pump, he hitched horses to either side. The observers were amazed that the force on the two hemispheres, held together only by air pressure, was poweful enough that horses pulling in opposite directions were not able to pull the copper shells apart.

The full name of the University of Magdeburg today is the Otto-von-Guericke Universität. The University's Web site is at: http://www.uni-magdeburg.de/