6. 17th and 18th Century Multi-disciplinary Scientists. Motion, Forces, Gravity and Light

The task of scientists is to describe natural phenomena and to elucidate nature’s laws. Three polymaths—Robert Hooke, Isaac Newton and Henry Cavendish—lived in the seventeenth century and were three of the most important scientists of the age, embarking on a host of ground-breaking multi-disciplinary studies. They are especially remembered for their theoretical postulations and experimental observations on gravity and light. Robert Hooke formulated the law of elasticity and investigated capillary action. He used a primitive compound microscope to examine slices of cork tree bark. He coined the word “cell”. He was described as England’s Leonardo da Vinci. His Micrographia is famed for its engravings of the miniature world. He identified fossils as remnants of once-living creatures. He offered a wave theory of light; suggested matter expands when heated; air is composed of small particles and is involved with combustion; that gravity is applied to all celestial bodies. Isaac Newton was the son of an illiterate farmer who achieved exceptional things. He is one of the most influential scientists ever to have lived, dominating the scientific view of the physical universe for about three centuries. Arguably, he had one of the greatest scientific minds in history—a creative genius in abstract thought and futuristic visions. Just as the world faced quarantine during the COVID-19 pandemic in 2020, in 1665–6, Newton isolated himself during the Great Plague. During two extraordinary years, he developed laws of gravity and motion; a new theory of light and co-invented calculus. He used mathematics and scientific principles to describe a diverse range of natural phenomena not understood at the time. Commentators referred to this period as his “annus mirabilis” or his ‘year of wonders’. His scientific work revealed a Universe that obeys logical mathematical laws. His laws of dynamics and universal gravitation have a reach that extends to the extremities of the Universe. He succeeded in combining laws that govern the motion of objects on Earth with those laws that determine the motion of celestial bodies. He put forward a unified theory of the Universe, describing bodies moving with clockwork predictability, albeit on a stage of absolute space and time. When America’s Mission Control directs a spaceship in the solar system, the trajectory will be determined, in part, using Newton’s calculus, together with his theory of gravity and his laws of motion. We now know that gravity is both a great creator and destructor of planets and galaxies. He related the observed ebb and flow of tides, as well as spring and neap tides, to the perturbing and varying gravitational forces exerted jointly by the Moon and Sun. He linked the precession of the equinoxes to the attraction of the Sun and the Moon on the Earth’s equatorial bulge. He solved problems associated with fluids in movement and of motion though fluids. He calculated and determined experimentally, the speed of sound waves. When investigating the refraction of light by a glass prism, he demonstrated the divisibility of white light into several coloured rays which could not be further sub-divided, but which could be reconstituted. Henry Cavendish approached every investigation with a strict quantitative examination. Like Robert Boyle, he was fascinated with gases, liberating them by heating solids or treating solids with acids. He investigated their properties, demonstrating that many were distinguishable from air which, at the time, was thought to be a unitary element. He performed experiments to determine the density of the Earth. From his data, others were able to enumerate the universal gravitational constant—one of physics’ fundamental constants. Cavendish co-founded the Royal Institution to introduce new technologies and diffuse scientific knowledge by public engagement. It is fitting that that Cambridge University’s world-renowned physics laboratory is named the Cavendish Laboratory, where many Nobel laureates have studied and conducted pioneering research.