Christians Huygens Christian Huygens (1629 to 1695) was probably the greatest Dutch scientist of his time. He was primarily a mathematician and physicist but also made contributions to astronomy using his own designed telescopes), biology (through his discoveries using microscopes of his own making), and the construction of clocks. He was the son of Constantin Huygens a famous poet and influential statesman and diplomat under the Dutch Republic. He had two other brothers and sisters. Being from an aristocratic family he was educated in languages (including French and Latin) drawing, law, science, engineering, mathematics and music. He is known to have said “science is my religion” (see Cosmos by Sagan pg 143). The Huygens family had many distinguished guests visiting the including Descartes. Huygens also had contact with Spinoza although he did keep this relationship polite but distant (he loaned Spinoza books and Spinoza did work grinding lenses for Huygens). Huygens had contact with other great scientists of his time including Gottfried Leibnitz who visited Huygens to study mathematics with Huygens. Huygens was also a member of French Academy of Science as well as the Royal Society in its early days. He kept an active correspondence with the members of the Royal Society including Isaac Newton, and Robert Hooke. He was greatly admired within these scientific communities. In the field of astronomy Huygens was one of the first to discover the rings of Saturn. He invented the pendulum clock that he hoped could be used to accurately measure time on ships in the opens seas. At this time navigation at sea had a very high priority for trade as well as for military strategy. Note: The idea of longitude is based on the fact that the earth rotates on its axis once every 24 hours. This means that it moves a total of 360 degrees in 24 hours meaning that each hour is equivalent to 15 degrees of longitude. An idea that came from Galileo was to use the moons of Jupiter as a reference point to record the time at any given geographical point on the earth and thereby observe its position at the local time. The difference in the apparent position of the reference point at a specific time in the local area could be used to calculate the longitude compared with a 0 geographical position i.e. the prime meridian. Accurate navigation required the determination of longitude which was not yet known. Therefore governments greatly encouraged the development of such clocks since longitude at sea could be calculated if one knew the time difference between two different geographic positions using a fixed reference point (e.g. position of the sun). Despite Huygen’s efforts the first chronometer that could accurately measure time at sea was invented by a clockmaker John Harrison in 1760. He developed a wave theory to describe the nature of light. Huygens considered that light behaved as if it travelled in waves in a vacuum similar to waves on the ocean. This differed from Newton’s idea that light was composed of particles. Red light was made up of larger particles than blue light. Actually both turned out to be right. Einstein later showed that a particle theory of light could explain the photoelectric effect (that a light beam shinning on a metal surface could knock off electrons). Modern quantum mechanics considers both the light behaves if it is composed of particles and as if it is composed of waves. He made early progress in describing the moving bodies and their collisions but never published them. Centrifugal force and gravity Huygens through experimentation with measuring the motion of pendulums, discovered that they exhibited constant acceleration. Through this work he derived formulas describe this motion and came also to describe motion in terms of centrifugal force around 1647. He saw that centrifugal force and gravity were related (today called the equivalence of gravity and inertial mass). He estimated “g” (the constant for the force of gravity) at 9.8 m/sec2. These discoveries were made independent of Isaac Newton. Discoveries in Astronomy Huygens believed as did Copernicus that the Earth moves around the Sun. This was widely accepted even by ordinary people in Holland at that time. Huygens even mentioned that Copernicus was acknowledged by all astronomers accept those who “were a bit slow witted or under superstitions imposed by merely human authority” (see Cosmos by Sagan pg 145). Christian philosophers during the middle ages argued that the heavens circled the Earth once a day and that it was not infinite in extent and therefore the existence of an infinite number or even a large number of worlds was not possible. The discovery that the Earth and not the sky moving and profound implications with respect to how unique the Earth was considered and whether there was life on other planets. Copernicus thought that the entire universe was heliocentric and Johannes Kepler did not think that stars had planetary systems. Huygens believed in the existence of other inhabitable worlds in the universe. Before he died in 1690, he published a book entitled “The Celestial Worlds Discover’d: Conjectures Concernng the Inhabitants, Plants and Productions of the Worlds in the Planets. In this book Huygens even speculated as to how the inhabitants of these other worlds would look . Huygens maintained that science was his religion and that the planets in the universe must be inhabited otherwise God had created them for nothing.

<b>Robert Hooke Renaisance Man of 17th Century England Life One of the most interesting early founders of the British Royal Society was Robert Hooke (1635-1703). No reliable likeness of him exists so no one knows what he looked like. Hooke was known for his competitive nature, for the quickness of his ingenuity, and for his quarrels with other scientist about the priority of discoveries and inventions. He was a kind of Renaissance man of the 17th century and was considered one of the most accomplished experimentalists of his time in that he designed and built various scientific devices including microscopes, telescopes, pendulum clocks (balance-spring watches), and vacuum devices. His response to any scientific problem was to invent a piece of equipment to resolve it. In this way, he considered himself a kind of “scientific craftsman.” He also helped redesign St Paul’s Cathedral in London together with Christopher Wren and provided surveying assistance to the team rebuilding London after the “Great London Fire” of 1666. Royal Society Hooke was appointed Curator of Experiments for the Royal Society. His duties involved the demonstration of various experiments for the members often using devices of his own making in order to test the experiments of others. He was appointed by his boss at that time, Robert Boyle, who was then one of the most well-known scientists of his time. Boyle employed Hooke to design customized experimental equipment and to investigate any topic that Boyle was currently interested in. These experiments included creating vacuums using air pumps, an experiment on respiration on a live dog whose thorax was cut open to show the beating of its heart and whose lungs were inflated by Hooke using a bellows (he never repeated this experiment because of “the torture of the poor creature”). Inventions and patents He was one of the first to devise a regulator for a marine clock that worked using springs instead of gravity. It functioned by causing a balance wheel that was attached to a spring to oscillate back and forth around its own center of gravity thereby facilitating a regular periodic interval for the stopping and starting of the clock. This allowed the measurement of units of time. Hooke never patented this invention and had a dispute with Christian Huygens over who had priority. He did manage to build a watch and presented to the King. Hooke asserted in the inscription on the clock that it had been invented as far back as 1658. Although Hooke lacked mathematics he sought to persuade through practical experimentation and formalized recording of data. Hooke invented or improved barometers, thermometers, and wind gauges. He recorded London’s weather regularly. This and other discoveries made by Hooke were quite often written in code in order to protect the priority of his claims. This was common practice in Hooke’s time to write up observations in code and file them as patents until deciding when to make these public. Often additional work had to be done on these entries before these discoveries could be revealed to the public. The first portable clock that could be used at sea to measure longitude was not invented until 1714 by John Harrison who won a prize of 10,000 pound from the English government. Discoveries Hooke’s law A physical law is named after Hooke which states that “a spring when stretched resists with a force proportional to the extension of the spring” (see The Discoverers, by Daniel Boorstin, pg 52). Redspot of the planet Jupiter Hooke’s discoveries in astronomy include the massive “redspot of the planet Jupiter” which today is known to be a massive storm area “40,000 kilometers long and 10,000 kilometers wide” (see Cosmos by Carl Sagan pg 136). He also observed the rings of Saturn as did his contemporary Christian Huygens and Galileo before them both. The Micorgraphia Hooke had made many observations of microscopic life using his microscope which had a higher magnification than the one originally designed by Antoine Leuwenhoek. He observed for instance thin layers of cork and was able to see regular square-like honeycomb structures that he called “cells.” This was the first time this term was used to describe these regular structures that make up all living animal and plant tissue. Robert Hooke’s most famous work was the “Micorgraphia” published in 1665. In this book Hooke states that “The Science of Nature has been already too long made only a work of the Brain and the Fancy. It is now high time that it should return to the plainness and soundness of Observations on material and obvious things.”(see Isaac Newton by James Gleick pg 62). In this book Hooke provided a description of the microscope and its uses. He presented 57 handrawn and engraving illustrations of what he saw under his compound microscope including the eye of a fly, the shape of a bee’s stinger, the anatomy of a flee and a louse, structure of feathers and the structure of plantlike molds (there were also engravings that included a thyme seeds). The book also presented Hooke’s theories of light and color as well as his theories about respiration and combustion. Hooke in order to improve the quality of the images he saw under the microscope invented a device that he called a “scotoscope (or a condenser in modern terminology).” This consisted of a glass globe filled with brine that he positioned between the light source and the lens of the microscope. He also placed a convex lens between the light source and the globe to focus the light source. He found that he could improve the quality of the images by adjusting the relative positions of the lamp, globe, and lens. Hooke also speculated on the nature of light and color. “Light is born of motion” he claimed. He stated that all luminous bodies are in motion and that we see two main colors red and blue that are caused by their impression on the retina of the eye by an “oblique and confused pulse of light.” At this point red and blue “met and crossed each other” to produce “different kinds of greens.” Hooke and Newton According to Gleick, Hooke was an inspiration to Newton who was actually 7 years younger than Hooke. Newton never admitted this and throughout their lives Newton was goaded by Hooke. Newton saw Hooke as his nemesis and tormentor. Hooke also became Newton’s victim. One famous dispute Hooke had with Isaac Newton was after the publication of Newton’s landmark work the “Principia” (Mathematical Principles of Natural Philosophy). Hooke claimed that many of the ideas presented by Newton were plagiarized from communication he had had with Hooke a dozen years before. (An interesting aside involved a dispute between Hooke, Christopher Wren, and Edmond Halley that they addressed to Newton. The asked Newton what he thought would be the best curve or path of the planets that would describe their motion around the Sun assuming that their force of attraction to the Sun would decrease with the reciprocal of the square of their distance from the Sun. According to this story, Newton immediately answered that the path would be best described by an ellipse. Halley asked him how he knew that and Newton claimed that he had calculated it. However after some searching he could not find the proof but said that he would derive it again and send it to Halley. This turned out to take 3 years (1684 to 1687) and resulted in the “Principia” Newton’s most famous work). (See the Ascent of Man by Jacob Bronowski pg 233) Newton was so upset by Hooke’s claims of plagiarism that he deleted all reference to Hooke’s work and even threatened to give up publishing the “Principia.” Newton so resented Hooke that he refused to assume the presidency of the Royal Society until after Hooke’s death. It is not entirely clear whether Hooke’s claims were true or not. However, Newton did not merely speculate on the ideas he discussed (as Hooke apparently did), but he also presented mathematical proofs for his ideas. Hooke may have had early insights into the ideas presented by Newton but he had not done the experiments to prove his hypotheses. Hooke also argued against Newton’s theory of the physical nature of white light. Newton described that white light is not modified by passing through a prism but instead it is physically separated when passing through a prism and this brings forth the characteristic spectrum. Hooke did not agree with this and the dispute must have been so vehement that Newton refused to publish his book on optics until after Hooke died