Though one of the most brilliant minds in history, the Dutch scientist Christiaan Huygens enjoyed relatively little fame during his lifetime. This was chiefly due to chronological factors, for Huygens worked during the period directly after the death of Galileo and just before the ascent of Isaac Newton (1642-1727), both towering figures of science. If not for the proximity of thesetwo geniuses, Huygens would have certainly been considered the greatest scientist of the seventeenth century. Though his work was unregarded for many years after his death, he is today held as one of the chief contributors to themodern sciences of mechanics, physics, and astronomy.
Huygens was born in The Hague, Netherlands, in 1629. The environment in whichhe was raised was ideal for the nurturing of young minds: his father, Constantijn Huygens, was a diplomat and poet who understood the need for classicaltraining, and he planned for his son a private education in mathematics, languages, literature, and music. Young Christiaan was also influenced by the mathematician-philosopher René Descartes, a friend of the Huygens familyand frequent visitor to their home. From Descartes Huygens learned of the "mechanistic" philosophy of nature, and came to believe that all natural phenomena would one day be explained by science.
Huygens left his home in 1645 to study law and mathematics at the Universityof Leiden and, in 1647, the College of Orange in Breda. He was unsatisfied with the universities' narrow approach to learning, however, and in 1649 he returned to The Hague. There he remained until 1666, living off an allowance from his wealthy father. Given the financial freedom to study as he pleased, Huygens began to perform some of the most important research of his life. As a child, Huygens had been interested in observing the night sky; however, the optical equipment available to him allowed little more than a blurry view of the heavens. By 1650, with the help of the Dutch philosopher Benedict Spinoza (1632-1677), he had taught himself the art of lens grinding. Developing a newmethod for grinding lenses of unparalleled clarity, Huygens began to chart the sky in earnest. During the period from 1655 to 1660, Huygens made a numberof landmark astronomical discoveries, including Saturn's ring and the planet's largest moon, Titan. He was the first to observe the surface features of Mars, as well as the Great Nebula in the constellation Orion.
In order to facilitate these observations, Huygens designed several new pieces of astronomical equipment. Chief among these were his lenses, which provided far greater resolution and magnification than any before. After several years he perfected an achromatic lens that corrected the "false color" fringes often associated with inferior lens systems; this lens, called the Huygenian eyepiece, is still used in many telescopes today.
In order to better view the sky, Huygens also modified the design of his telescopes. It was commonly known that longer telescopes, with their longer focallengths, allowed for greater magnification. Huygens took this principle to its extremes, constructing telescopes up to twenty-three feet (7.0 m) long. While these remarkable instruments gave a magnificent view of the planets, Huygens remained unsatisfied. He believed that the conventional telescope designwas too limiting, for it relied upon metal tubes which would bend if they were too long. His answer was a tubeless telescope called an aerial telescope. Because there was no tube to connect them, the large objective lens and the smaller eyepiece could be as far apart as practical lens construction would allow. The largest of these aerial telescopes was more than 100 feet in length.In addition to optical aids, Huygens also invented a micrometer in 1658 thatenabled him to measure the angular separations of objects (such as the apparent distance between Saturn and its moon) with a precision of a few seconds ofarc.
While Huygens observed the heavens, the European scientific community was working toward the development of a reliable timekeeping device. Such a device was in great demand by the trading industry, who required an accurate clock for use in the navigation of their sailing vessels. Previously, clocks were regulated by a slowly falling weight which would turn the device's gears. Unfortunately, the pace of the weight's descent was irregular, and the clocks werewildly inaccurate. Years earlier, Galileo had noted that a pendulum would swing with a precise motion, taking the same amount of time to move in one direction as it did to return. He termed this effect isochronicity ("equal time"),and suggested that it might be useful as a means for regulating timepieces;however, he was never successful in designing a working model. In 1656, Huygens found that a swinging pendulum was not truly isochronic unless the arc itdescribed was not completely circular. Using this knowledge he devised a system combining the pendulum with a weight-driven clock--the pendulum would swing exactly once each second, precisely regulating the motion of the clock's hands. The falling weight would drive the gears, as well as give the pendulum just enough energy to overcome the slowing forces of air resistance and friction.
Before the invention of Huygens' pendulum clock there was no reliable means of measuring time. Within months of the introduction of the "grandfather clock" design, towns across the Netherlands (and, soon after, all of Europe) had large clock towers regulated by swinging pendulums. Huygens' experiments withpendulums had given him an insight into the nature of motion itself.
Using the work of John Wall as a starting point, Huygens expanded his research to include the concept of momentum, a property of a moving object that measures its impact should it hit another object. His theory of momentum was included in his 1673 publication Horologux Oscillatoriux; it is now betterknown as the law of conservation of momentum. This law, a precursor to Helmholtz's law of conservation of energy, states that the momentum of a moving object (its mass multiplied by its velocity) remains constant unless the objectis slowed, stopped, or changes direction--that is, subject to a force. In the absence of force, momentum is conserved.
This was only the first of Huygens' forays into the field of theoretical physics. During the latter half of the 1600s, a great debate had divided the European scientific community: the nature of light. Newton, still a student but quickly gaining a reputation as Britain's most prominent scientist, had proposed the theory that light was composed of particles moving through a vacuum. His proof was the fact that, when shone through a prism, light would split into its individual colors--thus, white light must be a composite. This conceptwas contrary to Huygens' mechanistic view of the universe, a result of his childhood conversations with Descartes which demanded that all natural phenomena be the product of other phenomena--that is, that things happen because other things make them happen. Just three years after the publication of Newton'slight theory Huygens announced his own, stating that light moved in a longitudinal wave through an invisible substance called ether (in much the same wasas sound waves move through air). The light waves, according to Huygens, were produced by microscopic pulses emanating from the source; as they traveled,the pulses would push the ether longitudinally (back and forth), creating awave motion. At he time of its publication, Huygens' wave theory of light wasgiven little consideration, chiefly because scientists were reluctant to accept the notion of the invisible ether. As Newton's reputation grew his particle theory became more and more popular, and the work of Huygens was all but forgotten. It was not until the nineteenth century that Thomas Young re-introduced the wave theory of light--this time without the dubious presence of theether.
It is not surprising that Huygens earned little fame during his lifetime, forhe published his work slowly and infrequently. He was also something of a recluse, choosing not to take on students. However, he was instrumental in thefoundation of the French Academy of Sciences, and was a charter member of theBritish Royal Society. In addition to his clocks and his astronomical instruments, Huygens invented the manometer (a device used to measure the pressureof liquids and gases), as well as a prototype internal combustion engine using pistons.