Robert Hooke (1635-1703)

Robert Hooke (1635-1703)

Perhaps one of the greatest experimental scientists of the 17th century, Robert Hooke of Britain, left an enduring legacy in disciplines as diverse as physics, architecture, astronomy, paleontology, and biology. Modern microscopes, clocks, and automobiles all bear his imprint, and an important law of elasticity still shares his name.

Hooke was born the last of 4 children to a minister on July 18, 1634, at Freshwater, on the Isle of Wight. As a child, he suffered from a devastating case of smallpox that left him physically and emotionally scarred for the rest of his life. An unhealthy child, Hooke grew into a hunchbacked, pale, skinny, nervous hypochondriac. His father, John Hooke, took an active role in Robert’s early education until he entered the Westminster School at the age of 13 following his father’s suicide. After graduating from Westminster in 1648, Hooke first conducted an apprenticeship with artist Sir Peter Lely, and then entered Oxford University where he met and studied under some of the greatest scientists in England. Hooke eventually became a paid assistant for the renowned Irish physicist Robert Boyle and helped develop a working air pump. He remained in Boyle’s laboratory until 1662, when he was made Curator of Experiments for the Royal Society of London, a job that entailed demonstration of scientific equipment and experimental procedures during weekly meetings of the entire Society.

In 1663, Hooke was officially elected as a Fellow of the Royal Society, and 2 years later he received an appointment as professor of geometry at Gresham College. The latter position was accompanied by a suite of rooms at the college where Hooke lived and worked for the rest of his life. During this period, Hooke’s interest in microscopy and astronomy soared, and he published Micrographia, his best known work on optical microscopy in 1665. The next year, Hooke published a volume on comets, Cometa, detailing his close observation of the comets occurring in 1664 and 1665. After Henry Oldenburg’s death in 1677, Hooke succeeded to the post of Secretary of the Royal Society, which he maintained for the next 16 years.

Micrographia encompassed the first important set of observations using an early microscope equipped with compound magnifying lenses and was illustrated by elaborate drawings (his finely-detailed drawing of a flea is famous). Hooke observed a wide diversity of organisms including insects, sponges, bryozoans, diatoms, and bird feathers. Perhaps less well known, Hooke coined the term “cell” in a biological context, as he described the microscopic structure of cork like a tiny bare room or monk’s cell in his landmark discovery of plant cells with cell walls. Hooke was able to confirm Antonie Philips van Leeuwenhoek’s surprising observations of bacteria and protozoans, leading to the general acceptance of the Dutch scientist’s results by the established scientific community. Hooke, much preferring his compound microscopes, did not conduct a substantial number of experiments with Leeuwenhoek-style microscopes, and criticized these simple instruments as offensive to his eyes.

As the first to examine fossils with a microscope, Hooke noted the remarkable similarities between petrified wood and rotten oak wood in addition to fossilized shells and living mollusk shells. These observations helped move science past Aristotle’s misconceived notion that fossils formed and grew with the Earth and only imitated living things in nature, rather than the processes of speciation, fossilization, evolution, and extinction. Hooke’s archaic language certainly described processes explaining the mineralization of living tissue into fossils and hinting at extinction and evolution, two-and-a-half centuries before Charles Darwin. Micrographia also included a wave theory of light, which compared the spreading of light vibrations to undulating waves of water. Hooke followed the publication with a series of lectures on light to the Royal Society and was the first to describe thin film phenomena and the associated periodicity using membranes and thin plates of mica. In 1672, he noted that light vibrates perpendicularly to the direction of its propagation.

Being the first to give serious consideration to the importance of the resolving power of optical equipment, Hooke advanced both microscopy and the development of telescopes. His contributions to optical instrument evolution include many innovations to the microscope, exemplified by the invention of the compound microscope and the creation of an ingenious illumination system. Hooke developed a micrometer and was the first to apply telescopic sights to surveying instruments. A refractometer to measure the refractive index of liquids, the addition of a spiral gear to adjust the setting of telescopes, the universal joint (of automobile fame), the iris diaphragm, and a lens-grinding machine are all attributable to this British scientist, cartographer, and musician.

Endlessly fascinated by springs, Hooke noted that when an elastic body, such as a spring, undergoes stress, its shape is altered in proportion to the applied stress. Following extensive experimentation with assorted springs and coils, Hooke noted the link between extension and force, resulting in Hooke’s Law which posits that a spring’s extension is proportional to the weight hanging from it—for every centimeter of compression, the force increases by the same amount. If the stress applied to the body exceeds a predetermined number known as the elastic limit, the body will not revert to its prior form once the stress is removed. In equation form, Hooke’s Law is expressed:

$F=KA$
where F is the resisting force, A is the displacement, and K is the spring constant.

By explaining the science behind coil springs, the law made it easier to use springs in all manner of technology. From automobile suspensions to playground toys, to retractable ballpoint pens, springs eventually became basic mechanical components, in no small part because of the pioneering work done by Hooke.

It is revealing to note that Hooke’s Law was concealed in an anagram for 2 years to prevent competing scientists from claiming to have discovered the spring law on their own. He first described the finding in the anagram “ceiiinosssttuv,” whose solution he later published as “Ut tension, sic vis” which translates to “As the extension, so the force.” In doing so, Hooke was able to claim priority for his breakthrough without divulging the details.

Looking toward the stars as the inventor of the reflecting telescope, Hooke’s ventures into astronomy include the first inference to the rotation of Jupiter and the description of its Great Red Spot. He also observed the rotation of Mars and Jupiter, attempted to observe and describe parallax (the difference of orientation of an object viewed along 2 different lines of sight), and noted 1 of the earliest examples of a double star. One of the first scientists to build and use a reflecting telescope, Hooke showed the Earth and moon orbit the sun in an elliptical, rather than circular path. In addition to its voluminous references to optical microscopy, Micrographia includes notes on Hookes’ observations of lunar craters and speculates on their origin. He formulated the theory of planetary motion, as a problem in mechanics, which led Isaac Newton to his theories surrounding gravitational laws. Although his 20-year work on gravity was innovative, it lacked some of the mathematical sophistication of Newton’s, which quickly overshadowed Hooke’s theories and speculation. Early in their respective careers, the 2 prominent scientists showed a measure of respect for 1 another, with Newton writing a letter to Hooke featuring the famous line, “If I have seen further it is by standing on the shoulders of giants.”

Although he never had any formal training as an architect, Hooke was appointed as Surveyor of London after the Great Fire of 1666 devastated the city. Through numerous rebuilding projects, including the Royal Greenwich Observatory, Bethlem Royal Hospital, and St. Paul’s Cathedral, he proved his mettle as a designer. In the overall reconstruction of the city of London, Hooke suggested redesigning city streets on a grid layout with broad boulevards and cross streets, a blueprint later used in Liverpool, Paris, and several U.S. cities.

Hooke dabbled widely in the sciences and arts and is often referred to as the founder of meteorological sciences (he proposed setting 0°C as the freezing point of water). In Micrographia, he describes instruments he either designed or improved for advancing the store of scientific knowledge into weather systems. One of the devices used a wheel barometer to detect subtle changes in the rise and fall of mercury, thereby providing an indication of the atmospheric barometric pressure. Other weather-related inventions included the hygrometer for determining humidity, and the anemometer for gauging wind speed.

Hooke was 1 of the first scientists to claim that such weather phenomena as hurricanes and fog are byproducts of denser air. With uncommon foresight, he suggested that if daily weather information was compiled and analyzed, it could be possible to predict the weather.

A pioneer in early geology, Hooke was an expert in earthquakes and developed theories of combustion. He was a very active inventor and innovator of a wide spectrum of scientific instruments beyond his microscope work. These include the modern air pump, spring-driven watches, a depth-sounding machine, an air gun, carriages, windmills, a telegraph, a diving bell, surveying equipment, and various levels and scales. Hooke believed strongly that instruments were to be viewed as extensions of the human senses.

In a prime example of scientific ingenuity, Hooke helped solve a critical problem for seafarers: how to use a clock to determine longitude while on the open sea. Fluctuations in the Earth’s gravity, temperature changes, and humidity would cause errors in the clock’s mechanism, particularly the pendulum, which relied on gravity for its control. To deal with these issues, Hooke traveled to the West Indies (where gravity is less strong by the equator) and found the motion of the boat led to more errors in the pendulum swing of the clock. To deal with these obstacles, he created counterwound spiral springs and double balances to help offset the forces acting on the pendulum. Through sheer inventive skill, Hooke was able to assemble a pocket watch incorporating these compensating devices, earning the gratitude of mariners.

Historians have made frequent mention of the abrasive side of Hooke’s personality, beginning with his first biographer, Richard Waller, who wrote that Hooke was “despicable, melancholy, mistrustful, and jealous.” Those words influenced other writers for the next 200 years, forming a picture of Hooke as an unhappy, self-centered, unfriendly curmudgeon, an image prevalent in numerous books and assorted publications. One writer went so far as to describe Hooke as “cantankerous, envious, and vengeful,” and even the more sympathetic used words such as “difficult, suspicious, and irritable.”

It was not until the publication of Hooke’s diary in 1935 that another side of Hooke was revealed. In her interpretation of the diary, Margaret Espinasse writes that the depiction of Hooke as a morose and envious recluse is false. After being virtually forgotten during the 18th century, Hooke’s reputation was revived and after an extended period of obscurity he is now duly accorded with the recognition due to 1 of the most prominent scientists of his era.

Perhaps one reason for the prior lack of acknowledgment of his accomplishments is the diversity and intensity of his work. By spreading himself thin with a vast number of projects, explorations, and experiments he frequently neglected to take the steps, such as publishing, that were necessary to receive due credit for his efforts.

As England’s version of Leonardo da Vinci, Hooke’s reputation also suffered greatly during his lifetime because of intellectual property disputes and his apparent conflicts with other prominent scientists (who often had much more influence in the Royal Society). As an example, Hooke clashed with Christiaan Huygens over the spring regulator, and he had numerous battles with Isaac Newton, first over optics in 1672 and then again in 1686 over the inverse square law of gravitation. He never married, but diary entries reveal he did have affections for others. Tragically, Hooke died intestate in 1703 with 9,580 pounds to his name. His health had severely deteriorated during the last 7 years of his life, and he was plagued with an illustrious career that was greatly overshadowed by his mortal enemy, Isaac Newton. Historians investigating Newton’s Principia, and Hooke’s involvement in the early development of this famous volume, have since yielded some overdue credit. Unfortunately, Hooke’s only known portrait and many of his inventions and papers have not survived the centuries. Perhaps a good portion of this dilemma is attributable to Newton’s total disdain for Hooke, which was manifested in numerous and legendary attempts to obliterate Robert Hooke from any association with the Royal Society and his significant contributions to science. Even his gravesite remains a mystery. His remains were exhumed and reburied during the 1800s in North London, but the precise location is unknown. If his remains are found, officials with City University in London say they will use the latest facial reconstruction technology to give Hooke a face, and with it, some of the recognition he has been denied.

## The Hooke Microscope

Although Hooke did not make his own microscopes, he was heavily involved with the overall design and optical characteristics. The microscopes were actually made by London instrument maker Christopher Cock, who enjoyed a great deal of success due to the popularity of this microscope design and Hooke’s book. The Hooke microscope shared several common features with telescopes of the period: en eyecup to maintain the correct distance between the eye and eyepiece, separate draw tubes for focusing, and a ball and socket joint for inclining the body. The microscope body tube was constructed of wood and/or pasteboard and covered with fine leather. When the draw tubes were fully closed the microscope measured 6 inches long. Although the craftsmanship and design of this microscope was excellent, it suffered from a poorly executed focusing mechanism that would tend to wear very quickly and unevenly.