Vacuum | Research & Encyclopedia Articles

Vacuum

A vacuum is defined as a space devoid of matter.

Atomism, a ancient Greek school of philosophy which flourished about 400 B.C., held that a vacuum was an essential part of nature in which atoms--the discreet, indestructible units of matter--could interact and thereby create the universe. The Greek philosopher Aristotle, however, decreed that a vacuum could not exist. He correctly believed that the atmosphere had weight, and as air became less dense it would be possible to move faster through the atmosphere. Yet the next step of his reasoning went somewhat astray. In a complete vacuum, he reasoned, infinite speed would be possible because motion would encounter no resistance. Since he did not accept the possibility of infinite speed, he decided that a vacuum was equally impossible.

Aristotle's views endured as the familiar dictum "nature abhors a vacuum," and was used to explain the action of such inventions as suction pumps, barometers, and pistons. This view, however, began to change during the European Renaissance. The Italian astronomer and physicist Galileo accepted the horror vacui of Aristotle, but believed that nature's vacuum-abhorrence was limited. Pumps operated in mines had already proven that nature would only fill a vacuum with water up to a height of 30 ft (10 m).

Galileo encouraged his former pupil, Evangelista Torricelli, to investigate these supposed limitations. Torricelli, however, did not believe that vacuum-abhorrence was responsible for raising the water. Rather, he reasoned, it was the result of the pressure exerted on the liquid by the surrounding air. To prove his theory in 1643, he filled a glass tube--sealed at one end--with mercury and upended it into a dish also containing mercury. Only a portion of the tube emptied. 30 in (76 cm) of the liquid remained, a result of the downward pressure of the atmosphere on the mercury in the dish. Equally important, as the mercury emptied, a vacuum was created at the top of the tube. This, the first man-made vacuum, effectively disproved Aristotle's theory and affirmed the existence of vacuums in nature.

German physicist Otto von Guericke dramatically demonstrated the properties of a vacuum soon after Torricelli's experiment. He first invented an air pump to remove the atmosphere from a vessel and create a vacuum (the idea that air could be "pumped" just like water was in itself an exciting new concept). Using such vessels, he then proved that in a vacuum sound could not travel, candles could not burn, and animals could not live. In 1654 Guericke conducted one of his most flamboyant experiments before Emperor Ferdinand III. After evacuating the air within two sealed hemispheres, he attached teams of horses to each half and drove the teams in opposite directions. Although the horses exerted extreme force, the two hemispheres could not be separated until air was allowed to enter between them.

In 1657 Robert Boyle and his assistant Robert Hooke improved upon Guericke's air pump. He also proved Galileo's contention that objects would all fall at the same speed in a vacuum; Boyle simultaneously dropped a feather and a lump of lead in an evacuated cylinder and saw them hit the bottom together. In addition, he discovered that electrical attraction occurred through a vacuum, but a ticking clock in a vacuum could not be heard (Gasparo Berti had conducted a similar sound experiment with a bell in 1640).

Hooke speculated on the concept of using a vacuum to create an atmospheric engine. The vacuum would allow air pressure to "pump" water from one level to another. The first demonstration of this concept was made by Denis Papin (1647-1712) in 1690. In 1698 Thomas Savery (1650-1715) received a patent for a better designed atmospheric engine and used it to pump water out of mines. Another improvement was made by Thomas Newcomen (1663-1729), who was obligated to include Savery as a partner because of the patent. Newcomen's engine was slow and inefficient, but it was still better than its predecessors.

During the nineteenth century, the vacuum became an essential tool for physicists who would study electricity and the atom. In 1855 Heinrich Geissler (1814-1879) invented a vacuum container by moving a column of mercury up and down to evacuate the air from the vessel. Named the Geissler tube by a colleague of Geissler, this apparatus changed the course of physics research and eventually led to the discovery of the electron by Joseph J. Thompson.

In 1875 William Crookes developed an even more efficient vacuum container, named, not surprisingly, the Crookes tube. With an air pressure 1/75,000 of Geissler's tube, he could use it to study the radiation and luminescence that electricity created around a cathode, which eventually led to the invention of the cathode-ray tube. Crookes's technique for creating a vacuum also made the mass production of Thomas Edison's (1847-1931) light bulb possible.