Category: History of Science

In the late 1920s, the conceptual seeds of what would become the Big Bang theory were just beginning to emerge. At this time many scientists supported the Steady-State model. The discovery of Hubble’s Law by the American astronomer Edwin Hubble in 1929 added a significant piece of observational data in support of the expansion of the universe, a critical feature of the Big Bang Theory’s model. Hubble’s Law is the observation that galaxies are moving away from the Earth at speeds proportional to their distance away from the Earth. The further away a galaxy is from the Earth, the faster it is moving away.

The Cosmic Backdrop Before 1929

The early 20th century was a time of astronomical upheaval. For centuries, astronomers believed that the Milky Way galaxy was the entire universe. But in the early 1920s Edwin Hubble showed that this was not the case. Using the 100-inch Hooker Telescope at Mount Wilson Observatory in California, he identified Cepheid variable stars in the Andromeda Nebula. Using these stars as distant markers, he calculated their distance to be 900,000 light years away (later revised upwards to 2.5 million), and he was able to show the Andromeda was a separate galaxy. This realization increased the size of the universe from a single galaxy up to billions of galaxies. The known universe was now vastly larger.

Meanwhile, another astronomer, Vesto Slipher, had been measuring the spectra of spiral nebulae since 1912. He noticed that most of these nebulae showed a “redshift”, meaning their lights stretched toward the red end of the spectrum indicating that they were moving away from us. Since at the time nebulae were not thought to be other galaxies, Slipher did not realize the significance of his observations. By 1925, Slipher had measured redshifts for 42 galaxies, with velocities up to 1,800 kilometers per second.

Piecing the Puzzle Together: Velocities, Redshifts, and Distances

Hubble combined Slipher’s velocity data with his distance data and in 1929 he published his findings in the Proceedings of the National Academy of Sciences. Hubble discovered a rough but undeniable linear relationship between a galaxy’s redshift velocity and distance from Earth that could easily be plotted on a graph. The relationship can be written as v = H₀ d, with v as recession velocity, d as distance, and H₀ as the Hubble constant – a measurement of how quickly space is stretching.

Hubble’s law is sometimes referred to as the Hubble-Lemaitre Law because of the work of a Belgian priest and astronomer, George Lemaitre. In 1927, Lemaitre independently worked out Hubble’s law, arguing that the field equations from Albert Einstein’s General Theory of Relativity showed the universe is not static. To keep the universe static, Einstein added a coefficient he called the cosmological constant. Lemaitre went further, and he took some of the available redshift measurements, combined them with the available distant measurements, and noticed a linear trend between the two. However, his work was published in a little read French journal, so its impact was minimal, and Lemaitre opted to cite Hubble’s better and stronger data in giving credit to Hubble for the discovery of the law. After Hubble’s publication, Einstein abandoned his concept of a cosmological constant, calling it the “biggest blunder” of his career, although it’s been revived in recent decades to account for dark energy.

The implications of Hubble’s law are important. If galaxies are all expanding from each other, then rewinding time suggests they all more crammed together. Rewind time far enough, back to the beginning of the universe, and you arrive at a dense, hot beginning – the Big Bang.

Initial Skepticism and Hubble’s Legacy

Hubble’s original value for his constant implied a universe younger than the Earth, puzzling scientists and shedding doubt on his results. Better telescopes, resulting in improved distance measurements, resolved this in the coming decades. Modern estimates place the Hubble constant near 70 km/s/Mpc, yielding an age of 13.8 billion years. The Hubble Space Telescope, launched by NASA in 1990 and named in his honor, has carried Hubble’s discovery into orbit, using Hubble’s law to map the expansion of the universe across billions of light-years.

Hubble’s 1929 breakthrough stands as one of astronomy’s greatest triumphs. Within a few years it elevated Georges Lamaitre’s previously ignored 1927 “Big Bang” theory from mathematical curiosity to mainstream cosmology. In the process it transformed our picture of reality from a static, island universe to the vast, to the expanding cosmos from a beginning that we know of today. Nearly a century later, Hubble’s Law remains the central pillar of observational cosmology.

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The discovery of antibiotics marked a historic milestone in the history of medicine.  Antibiotics are molecules that kill the growth of bacteria and have led to saving countless lives. As far back as 2500 BCE the Egyptians used moldy bread and plant extractions to treat infection wounds, a practice also used in ancient Greece and China.  The remedies were based on empirical observation rather than an understanding of the underlying biological mechanics.  We sometimes forget the concept of a microorganism as an agent of disease was only developed in the 19^th century by Louis Pasteur.

The Dawn of Antibiotics: Alexander Flemming’s Discovery of Penicillin

The discovery of antibiotics began in 1928 with Alexander Fleming’s accidentally discovery of penicillin. Flemming was Scottish bacteriologist working at St. Mary’s Hospital in London. He was experimenting with the Staphylococcus bacteria, a common bacterium responsible for infections such as boils, sore throats, and abscesses. In the late summer Flemming took a two-week vacation, but he left his lab with unwashed petri dishes. When he returned, he noticed that the petri dishes had been contaminated by a bluish green mold, and around this mold was a clear zone where the bacteria had been eliminated. 

The mold belonged to the genus of fungi called Penicillium. Flemming became intrigued by what he saw and began isolating and experimenting with the mold. He discovered that through a chemical substance the mold secreted, it could kill or inhibit a wide range of harmful bacteria. Furthermore, it left human cells untouched, suggesting that it could be used for safe treatment in the human body. Flemming named the substance Penicillin, after the mold.

In 1929 he published his findings in the British Journal of Experimental Pathology, noting that penicillin was effective against many disease-causing bacteria like streptococcus and meningococcus. However, the substance was unstable and difficult to purify and for nearly a decade the discovery remained largely overlooked by the broader scientific community.

The Oxford Team

Despite this groundbreaking observation, penicillin remained largely ignored by scientists for over a decade. In the late 1930s Howard Florey, an Australian pathologist, and Ernst Boris Chain, a German biochemist, were working at Oxford University. They rediscovered Flemming’s paper and quickly recognized its significance as a naturally occurring antibacterial substance. They faced several challenges including how to grow enough mold, how to extract and purify the ingredient, and proving their ideas could work. An Oxford team was put together, led by Florey, Chain, and Norman Heatley, to overcome these difficult challenges.

The first human trial came in 1941 on a policeman dying of horrific infections.  The officer made an impressive recovery; however, supplies ran out and he died a few days later.  Subsequent trials on wounded soldiers proved unequivocally that penicillin worked miracles where all else failed. World War Two provided an urgent need to develop penicillin as a treatment for soldiers, however British manufacturing was already under heavy strain due to the war. Later that year Florey and Heatley traveled to the United Stats to enlist American pharmaceutical companies and the US government’s support. Within two years, penicillin was being manufactured in quantities sufficient for military use.

The Antibiotic Boom

Penicillin’s success causes a global sensation and the race to discover new antibiotics was on. The post-war age saw an explosion of antibiotic discoveries. Pharmaceutical companies quickly isolated antibiotics from soil microbes, an area that proved to be a treasure trove of new antimicrobial compounds. These new drugs continued to transform medicine by making surgery safer, increasing infant mortality, and assisting in public health. Optimism was sky high in the 1960s that antibiotics could eliminate or reduce many infectious diseases. Their use eventually extended beyond medicine and into agriculture where they were used in animal livestock. However, there were early warnings about their limitations. 

As early as 1945 Flemming cautioned in his Nobel Prize acceptance speech that bacteria could develop resistance to penicillin if used improperly. This proved to be true. Bacteria can and regularly does evolve resistance to antibiotics, by means of producing enzymes that degrade the drug or alter their cellular targets. Since they reproduce rapidly, going through several generations per day, it allows for a high mutation rate in a short amount of time. In a bacteria population most of the bacteria is low resistance to the antibiotic, but a few may be high resistance. The high resistance bacteria survive and reproduce, over time eventually taking over the population. What began as a population with little to no resistance becomes a population fully resistant to the antibiotic, and a new drug is needed to kill the new resistant bacteria. Overuse in medicine and agriculture accelerated resistance, exposing a critical flaw in the discovery of antibiotics: bacteria adapt faster than new drugs can be developed. Despite this challenge the discovery of antibiotics remains one of humanity’s greatest medical achievements, but its future depends on balancing innovation with responsibility.

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In 1600 the English physician and natural philosopher William Gilbert published “De Magnete” (On the Magnet, Magnetic Bodies, and on the Great Magnet of the Earth), a pioneering six volume treatise on magnetism and electricity that was the culmination of his eighteen years of study and experimentation.  This seminal work of Gilbert laid the foundations for the scientific study of magnetism and was so thorough and complete that hardly anything new of value was added to the field until the discovery of electromagnetism by Michael Faraday in the 1820s.

William Gilbert and his Experiments on Magnetism and Electricity

William Gilbert was born on May 24, 1544 in Essex, entered the medical profession and became a successful and wealthy physician, a career that culminated in becoming Queen Elizabeth I personal physician.  As was the case with most natural philosophers of his time, his wealth provided him the leisure time to work as an amateur scientist, and while he was originally interested in chemistry, he eventually settled on studying magnetism, a phenomenon that up to that time had essentially been ignored by science.  During his time working in the medical profession, Gilbert simultaneously conducted his research on magnetism and electricity.  

Gilbert made several claims about magnetism in his book.  He commented on magnetism in nature, experimenting with different materials, but in particular he carried out experiments using a lodestone.  The properties of the lodestone were known for centuries, but hardly anything was known about how or why it worked the way it worked.  Gilbert identified the lodestone as a naturally occurring magnet that was capable of attracting iron and other materials.  He noted that the attraction was not only directional, but that it also varied over distances.  As the distance increased the magnetic force became weaker.  He showed the lodestone could induce magnetism in other materials.  For example, when iron was brought into contact with it, the iron acquired its magnetic properties. 

Gilbert was the first person to distinguish between north and south poles, while coining their names.  Through his experiments he demonstrated that like poles repel each other, while opposite poles attract. 

One of Gilberts most significant claims was that the Earth works as a giant magnet, with its magnetic field affecting the needle of compasses.  He conducted experiments to show how a compass needle aligns with the Earth’s magnetic field.  He also identified the Earth as having magnetic poles.  The experiments he conducted showed compass needle points towards a magnetic north, rather than a geographic north pole.  In his book, he described experiments where he suspended a magnetized needle freely and observed that it consistently pointed towards the magnetic north, independent of its original orientation.  He described in detail the behavior of the compass in various locations.  These observations became crucial for navigation.

Impact of De Magnete

The late Renaissance was a period of increasing scientific curiosity, but it was still heavily entranced in Aristotelian philosophy.  When considering the impact of De Magnete, the book had an impact in what he discovered for sure, but what was truly revolutionary was how he made his discoveries.   Not only did it expand our knowledge about magnetism, but it aided in changing the way people did science.  Gilbert established the scientific method as his means to discovery and it had a direct impact on the future generation of scientific minds, especially on Galileo Galilei and later on Isaac Newton.  

However, the immediate impact of De Magnete was probably most felt on navigators and explorers.  The compass had been around prior to the book’s publication but there were many misunderstandings and superstitions associated with it.  Gilbert laid the foundations for geomagmatism, allowing for better understanding and design of the compass.  Finally, navigators could begin to understand why the compass worked, leading to better techniques associated with its usage and less fear and guesswork of a “cursed” instrument.

Lastly, Gilbert’s ideas provided a catalyst for the further study of magnetism.  Future scientists such as Johannes Kepler explored magnetic forces in cosmology while later researchers, such as Carl Friedrich Gauss, formalized the mathematics of geomagnetism.  He also distinguished the difference between static electricity and magnetism, inspiring the work of Michael Faraday, Hans Christian Orsted, culminating in their unification as electromagnetism by James Clerk Maxwell.

William Gilbert’s work was clearly ahead of his time, but it planted the seeds of which the modern scientific method grew out of.  His work is a testament to the power of curiosity and experimentation – a legacy as magnetic as the forces he sought to understand. 

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The invention of the Leyden jar stands as a cornerstone in the history of electrical engineering. Often hailed as the world’s first electrical capacitor, this revolutionary device allowed scientists to store and release electrical energy – a feat previously thought impossible. Emerging in the 18th century, the Leyden Jar transformed the study of electricity, paving the way for modern innovations in science and technology.

The Invention of the Leyden Jar: Understanding the First Capacitor

During the 18th century the mysterious phenomenon of electricity was becoming a hot topic among learned men of science. Electricity could only be created and observed in the moment. One of the mysteries to be solved was whether electricity could be stored for later use and how to accomplish it. The invention that solved the mystery became known as the Leyden jar, named after the city of an early inventor of the device.

The Leyden Jar is typically credited to two individuals, who independently came up with the same idea.  In Germany, Ewald Georg von Kleist, a cleric and a scientist, was experimenting with electricity.  He was attempting to store electricity with a medicine bottle filled with water and a nail inserted through a cork stopper.  He charged the jar by touching the nail with an electrostatic generator, and he assumed that the glass jar would prevent the electricity from escaping.  While holding the glass jar in one hand, he accidentally touched the nail and received a significant shock, proving that electricity was indeed stored inside the jar. Von Kleist’s findings, however, remained obscure, as he didn’t widely publicize his work. Fortunately, the idea didn’t stay hidden for long.

Around the same time another man experimenting with electricity named Peter van Musschenbroek, of Leyden, Netherlands. Van Musschenbroek was a respected physicist and professor at the University of Leyden, where he also stumbled upon the same invention.  Musschenbroek’s device was much like von Kleist’s jar.  It consisted of a glass jar filled with water that contained a metal rod through a cork sealing the top of the jar.  The outside of the jar was coated with a metal foil.  When an electric charge was applied to the metal rod it was found that electricity could be stored in the jar.  Unfortunately for the person touching the metal rod, a significant shock was received. As Musschenbroek recorded what happened when he first touched the rod:

Suddenly I received in my right hand a shock of such violence that my whole body was shaken as by a lightning stroke…. I believed that I was done for.

Refining the Leyden Jar: From Shock to Science

It didn’t take long until Musschenbroek’s Leyden jar was being used and improved by others.  In 1746, the following year, the English physician William Watson improved the jars storage capacity by coating both the inside and outside with metal foil.  Also that same year, the French physicist Jean-Antoine Nollet discharged a Leyden jar in front of the French King Louis XV.  During the demonstration, Nollet arranged a circle of 180 Royal Guards, each holding hands and he passed the charge from the Leyden jar through the circle.  The shock was felt almost instantaneously by all members of the Royal Guard, to the delight of the King and his court.  Demonstrations such as this brought widespread attention to the exciting new field of electricity. Although these demonstrations were not purely entertainment as they showcased they Leyden jar as a potential scientific instrument.

Impact and Legacy of the Leyden Jar

Prior to the invention of the Leyden jar, electricity could only be observed and experimented at the moment it was created.  The Leyden jar changed this by allowing scientists to store electrical energy and use it when needed.  Researchers could now conduct various experiments related to electric discharge, conductivity, and other electrical phenomena.  As an added bonus, the jar was easily transported, especially compared to the electrostatic generators of the day.  The jars could be linked together to provide additional storage capacity.  These abilities contributed to the growth of knowledge in the field of electrical science.  

One famous usage of the Leyden Jar was by the American scientist and statesman Benjamin Franklin, when he conducted his legendary kite experiment in 1752.  In that experiment, Franklin flew a kite during a lightning storm in an attempt to prove that lightning was a form of electricity.  He attached a metal key to the end of the kite, and the key was then connected to a Leyden jar.  Despite some popular accounts of the experiment, lightning likely never struck the kite directly or else Franklin would have been killed. However, he was able to observe that the Leyden jar was being charged, thus proving the electric nature of lightning.  

The Leyden jar is also considered the first electrical capacitor, which today is a fundamental component in modern electric circuits.   The invention of the Leyden jar laid the groundwork for the development of more sophisticated capacitors.  While they briefly feel out of use after the invention of the battery, the basic idea of the Leyden jar capacitor found a renewed use at the end of the 19th century in modern electronic devices, albeit in a much smaller form. 

Overall, the Leyden jar played a pivotal role in the early explanation and understanding of electricity.  Its impact shapes the subsequent development of electrical technology and science.  

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The neutron was discovered by the British physicist Sir James Chadwick in 1932, marking a pivotal moment in the understanding of atomic structure. It was, in a way, the culmination of a series of scientific investigations of the subatomic particles of the atom that spanned several decades. The identification of the neutron provided answers to questions about the mass of the atom, ultimately leading to important developments in nuclear physics.

Developments that Led to the Discovery of the Neutron

In 1897, J. J. Thompson discovered the electron, a subatomic particle with a negative electrical charge. This discovery provided the evidence that atoms were composed of smaller particles. Two decades later, Ernest Rutherford discovered the proton, a subatomic particle with a positive electrical charge. Rutherford proposed a model of the atom with a dense, positively charged nucleus at its center, orbited by negatively charged electrons. However, this model presented a problem. The positively charged protons in the nucleus should all repel each other, causing the nucleus to burst apart. Yet, this did not happen as the nucleus is obviously stable, and the reasons for this stability were not understood at the time. The existence of a neutral particle was postulated by Rutherford as early as 1920.

The Discovery of the Neutron

This discovery of the neutron was the culmination of a series of successive experiments, worked out by several scientists in the late 1920s and early 1930s. In Germany, Walter Bothe found that beryllium exposed to alpha particles produced a new form of radiation. Bothe attempted to explain this sradiation in terms of gamma rays, because it was not deflected by either electric or magnetic fields. All known particles at the time (electrons and protons) contained a charge.

Taking this information a step further, the French husband-and-wife team of Irene Joliot-Curie (the daughter of Pierre and Marie Curie) and Frederic Joliot reported results from an experiment in January 1932 that led to to neutrons discovery. In the same vein as Bothe, their experiment involved the bombardment beryllium by alpha particles. They noticed that the radiation could eject protons from hydrogen-rich substances such as paraffin.  This was puzzling because gamma rays should not have enough energy to be able to knock out protons in this manner. In other words if this unknown radiation was indeed gamma rays then the law of conservation of energy was being violated.

Back at the Cavendish Laboratory in Cambridge, James Chadwick, a college or Rutherford, quickly became interested in these results.  Chadwick and Rutherford had been working on and off over the past decade in identifying the missing neutral particle suspected to be in the atomic nucleus.  This background allowed Chadwick to move quickly.  He also conducted a series of experiments where he bombarded light elements, such as beryllium, with alpha particles.  He noticed the same radiation being emitted which was not deflected by electric or magnetic fields.  However he interpreted the results differently than the others who conducted similar experiments. His observations led him to correctly conclude that the radiation was composed of uncharged particles. He used the laws of conservation of momentum and conservation of energy to calculate that the neutron has a mass similar to that of a proton.  He presented this as evidence of a new subatomic particle, which he detailed in a paper published in 1932 and named the neutron.  For his work he was awarded the Noble Prize in Physics in 1935.  

Impact of the Neutron’s Discovery

The discovery of the neutron was a key piece of the puzzle that allowed scientists to understand the binding energy of the atomic nucleus.  It had enormous impacts in both applied and theoretical physics.  

The discovery of the neutron explained the missing mass in atomic nuclei.  This in turn helped to explain the existence of isotopes – variants of elements with the same number of protons but different atomic weights – and therefore different numbers of neutrons in the atomic nuclei.  It also advanced the understanding of radioactive decay processes.  

The most important impact of the discovery of the neutron was in nuclear physics.  The neutron – a particle without an electric charge – was the crucial component in the development and study of nuclear fission, which occurred in 1938 by Otto Hanh and Lise Meitner.  The development of nuclear fission was quickly applied the development of nuclear energy and weapons.  The neutron plays the key role in the chain reactions that occur in both nuclear reactors and atomic bombs.  It is probably fitting then, that James Chadwick was placed as head of the British team that work on the Manhattan Project that produced the world’s first atomic bomb. 

Beyond nuclear fission, the discovery of the nucleus aided in our understanding in the nuclear processes that power the stars through the process of nuclear fusion.  The study of this process had advanced our understanding on the origins and evolution of the elements.  

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It has been famously stated that if Albert Einstein hadn’t published his theory of special relativity, someone else likely would have within the decade. But if Einstein hadn’t published his theory of general relativity we would still be waiting on that discovery to this day. The theory of general relativity, proposed by Einstein in 1915, is one of the most profound and revolutionary achievements in the history of science and transformed our understanding of space, time, and gravity.

Background on the Theory of General Relativity

For nearly two centuries, Isaac Newton’s law of universal gravitation stood unquestioned and unchallenged in the field of physics.  However, around the end of the 19th century some tiny, yet vulnerable, kinks in its armor were beginning to emerge.  Physicists noticed it was unable to explain certain phenomena, such as the orbit of Mercury.  They were also struggling to reconcile classical mechanics with new observations of the nature of light and electromagnetism.   A relatively unknown physicist at the time named Albert Einstein provided the solutions to these vexing problems.

Einstein’s journey towards his theory of general relativity began in 1905 with the publication of his theory of special relativity.  Special relativity primarily focuses on objects moving at a constant speed.  It ignores acceleration, or objects affected by gravity, which Einstein determined are essentially the same thing after he formulated general relativity.  

Between 1907 and 1915 Einstein worked extending of his theory of special relativity to include gravity.  The mathematical complexity of this task proved enormous, and so Einstein had to learn various advanced mathematical techniques to complete his ideas.  He worked with other mathematicians the help him understand the underlying math needed to formulate his ideas. 

Space, Time, and a Sliver of Curvature

In November 1915, Einstein presented his revolutionary ideas on general relativity to the Prussian Academy of Science. His theory describes how mass and energy curve the fabric of spacetime, effectively producing the force of gravity.  Therefore, a major implication of general relativity is that it redefined gravity from a force acting at a distance to a description of gravity as a geometric property of spacetime. The core of general relativity is the field equations, which explain the geometry of four-dimensional spacetime to the distribution of mass and energy within it. These equations are known as the Einstein field equations.  

General relativity also implies an equivalence principle.  This states that the effects of gravity are locally indistinguishable from the effects of acceleration. In other word, someone in a closed space cannot determine whether they are feeling the effects of gravity or acceleration.  A classic example is the elevator thought experiment.  Imagine you are in an elevator with no windows.  If you drop an object it falls to the floor at an acceleration of 9.81 m/s^2 due to earth’s gravity.  However, you could also be in distant space, far away from any gravitational force accelerating at a constant rate of 9.81m/s^2.  In the second scenario when you drop an object it will also fall to the floor at an acceleration of 9.81m/s^2 – the effects of the two scenarios are indistinguishable.  

Testing and Acceptance

General relativity has been repeatedly verified by observation and experimentation.  One of the first key confirmations of general relativity came in 1919 during a solar eclipse expedition by Sir Arthur Eddington.  To goal of the expedition was to measure the apparent shift of the stars near the sun during the solar eclipse.  Indeed, the observed shift matched the predictions made by general relativity.  

Another significant test of general relativity was the perihelion precession of Mercury’s orbit.  Mercury’s orbit exhibits a small deviation in the orientation of its elliptical orbit over time, a phenomenon known as perihelion precession.  Prior to general relativity, astronomers struggled to account for the advance of this phenomenon.  Newtonian classical mechanics failed to explain the discrepancy.  However, when Einsteins equations of general relativity were applied to this problem, they yielded an answer that matched the observed rate of precession.  This successful prediction, along with the results of Eddington’s experiment, provided crucial empirical evidence for the validity of general relativity.  General relativity also predicts other phenomenon such as gravitational redshift and time dilation, both of which have been confirmed through experiments as well.

As empirical validation rolled in, general relativity gradually began to gain acceptance within the scientific community.  By the latter half of the 20th century, general relativity had become fully accepted and became one of the two twin pillars of physics – along with quantum mechanics.  The acceptance of general relativity can be viewed as a watershed moment in the history of science, marking the transition from the Newtonian worldview to that of a relativistic worldview.  

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The existence of a form of light other than visible light was inconceivable prior to the 19th century. However, in nature there exists a continuum of radiation waves, all traveling at the same speed of light, with a nearly infinite possibility of wavelengths and frequencies. This is the electromagnetic spectrum, and the first new form of light was unexpected discovered in 1800 by the British scientist William Herschel.

The Discovery of Infrared Rays

William Herschel is best know for his discovery of the planet Uranus but his interests also extended beyond the visible universe. Herschel was fascinated by the nature of heat and light and his involvement in this area of study lead to the discovery of a completely new and unexpected form of light.

In 1800 Herschel conducted an experiment where he directed sunlight though a glass prism to create a spectrum of visible light. He then measured the temperature of the different colors of light, where he noticed the temperature increased as he moved from the violet to the red end of the spectrum. Then in a moment of true scientific curiosity, he took his experiment one step further. He decided to measure the temperature just beyond the red light, but where no sunlight was visible. This region showed the highest temperature of all, and this led Herschel to conclude that there must be some form of invisible light present that we cannot see. He named this invisible radiation infrared, from the Latin ‘infra’ meaning “below” – or in this case below the red in the spectrum.

The importance of this discovery can hardly be overstated. It added an entirely new dimension to our perception of the universe and to this day has had significant practical applications in a variety of fields such as astronomy, telecommunications, healthcare, and environmental science. It also suggested that there may be other forms of light yet to be discovered.

A Continuous Spectrum of Electric and Magnetic Fields Oscillating Together

Shortly after Herschel discovery of infrared rays, the German chemist Johann Wilhelm Ritter discovered another of invisible rays. Ritter was obviously inspired by Herschel’s discovery of infrared rays, and he decided to experiment at the opposite end of the spectrum, beyond violet. Ritter conducted his experiment by also focusing sunlight through a glass prism to create a spectrum of colors. He noticed that silver chloride, a chemical known to darken when exposed to sunlight, darkened faster when exposed to the region beyond violet light. He had discovered what would later become known as ultraviolet rays, from the Latin ‘ultra’ meaning “beyond” – in this case beyond violet in the spectrum. The discovery of ultraviolet and infrared rays further prompted the discovery of other types of electromagnetic rays.

In the 1860s the British physicist James Clerk Maxwell revolutionized the world of physics with his electromagnetic theory. He developed four mathematical equations, known as the Maxwell Equations, that described how electric and magnetic fields interact. These equations unified the previously separate fields of electricity and magnetism. His new theory suggested that light was a form of electromagnetic wave, and that it was just a smaller part of a much broader spectrum. This spectrum is known as the electromagnetic spectrum. In 1867, Maxwell predicted that there should be wavelengths of light longer than the infrared rays discovered by Herschel.

It took another two decades, but in 1887 the German physicist Heinrich Hertz confirmed Maxwell’s predictions when he discovered radio waves in his laboratory. Light with wavelengths of a shorter length were soon discovered next. In 1895 Wilhelm Roentgen accidentally discovered what became known as X-rays while experimenting with cathode ray tubes. It took another two decades until scientists were able to determine that these X-rays were indeed another form of light. The last part of the spectrum to be discovered was gamma rays. The French physicist Paul Villard discovered these in 1900 while he was studying radiation emitted by radium.

Far Reaching Technological Impacts

The discovery of the electromagnetic spectrum has had far reaching impacts on 20th century technology and beyond. The development of radio and television technology was predicted on the understanding of radio waves. In similar fashion, the invention of radar during World War II was possible due to the understanding of microwaves.

From science and technology to medicine and daily life, the impacts of the electromagnetic spectrum are almost too vast and numerous to mention. But to name a few – radio and television broadcasting, mobile phones and the internet, X-rays used in healthcare, space telescopes and satellite-based sensors are just a few of the many examples of the areas in which electromagnetic radiation have had an impact on civilization.

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Plate tectonics is a scientific theory that explains the movement of the Earths surface and many of its most prominent geological features. It is responsible in forming the deepest trench in the ocean to the tallest mountain on land – and in the ocean as we’ll soon see.  The uppermost layer of the Earth is called the lithosphere and is composed of large rocky plates that are on top of a lower molten layer of rock called the asthenosphere.   A convection current is generated between the two layers, causing the plates to glide at a rate of a few centimeters per year.  While it may not seem like much, given enough time this process has formed many of the geologic features of our planet.  It has resulted in the formation of the Himalayas and the separation of the South American and African continents. 

History of Plate Tectonics

The theory of plate tectonics is a relatively new idea, however fragments of ideas can be found in earlier times. In 1596 cartographer Abraham Ortelius observed that the coastlines of Africa and South America could be fitted together like pieces of a jigsaw puzzle.  He speculated that the continents may once have been joined, but have since been ripped apart by earthquakes or a flood.  Creationist have ceased on this idea to “prove” the existence of Noah’s Flood.  It does provide for an arresting image, as Richard Dawkins points out, of South America and Africa racing away from each other at the speed of a tidal wave. In the 1850s there was a noticeable correlation of rock type and fossils discovered in coal deposits across the two continents.  1872 saw the mapping of the Mid-Atlantic ridge. 

In the early 20th century a few versions of a continental drift began making an appearance but there was one that stood out in its influence and the development of the Earth sciences. In 1912 Alfred Wegener published two papers where he proposed his controversial theory on Continental Drift.  He suggested that in the past all landmasses were arranged together into a supercontinent that he called Pangaea (meaning “all lands”).  However he did not have a geological mechanism for how the landmasses drifted apart and the idea was met with much skepticism first. Over a period of decades Wegener continued to amass evidence for his theory and continued to promote his model of continental drift. He gathered evidence from paleoclimatology to provide a further boost to the idea. He noticed glaciations in the distant past occurring simultaneously on continents that were not connected to each other and were outside the polar region. Unfortunately, while in Greenland on an expedition for some of this data, Many of his specific details have turned out to be incorrect but his overall concept that the continents were not static and did move over time has been proven correct.

During the middle of the 20th century more evidence began to support the idea that the continents did move. Huge mountain ranges were being mapped on the ocean floor. It was assumed by both supporters and opponents of continental drift that the sea floor was ancient and would be covered with huge layers of sediment from the continent. When samples were finally obtained it showed all of this was wrong. There was hardly any sediment and that the rocks were young, with the youngest rocks being found near the ocean ridges. In 1960 the American geologist Henry Hess pieced all of this evidence together in his theory of sea-floor spreading. The ocean ridges were produced by molten lava rising from the asthenosphere. As it rose to the surface the magma cooled, forming the young rocks, and spreading the ocean floor in conveyor belt like motion through the slow process of convection. While some parts of the Earth were creating new oceanic crust and spreading the continents apart, other parts were doing just the opposite. Along the western edge of the Pacific for example, thin layers of oceanic crust were being forced beneath the thicker layer of crust, being driven down into the mantle below. This explains the presence and high frequency of earthquakes and volcano’s in places like Japan.

By the beginning of 1967 the evidence of continental drift and sea-floor spreading was quite strong and ready to be assembled into a complete package. That year Dan McKenzie and his colleague Robert Parker published a paper in Nature introducing the term plate tectonics for the overall package of ideas that describe how the Earth’s plates move and the resulting geological features it creates. To this day many details are still being flushed out but this moment marked a revolution in the Earth Sciences. It is relevant now only in geology but also in its synthesis with the evolution of life on Earth.

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