Almost all of our knowledge of the wider Universe has been obtained by studying the information brought to us through the vacuum of space by different parts of the electromagnetic spectrum.   But for most of human history astronomers have only had a narrow mixture of wavelengths with which to observe.   All that started to change one summer in Lincolnshire, England.   A young Isaac Newton,  bored because he had been sent home from Cambridge University when it had been closed because of plague, started to put his mind to matters that had puzzled humankind for millennia.

1666

A student once professed amazement to me that Isaac Newton discovered the visible spectrum in the summer of 1666.   "That's amazing" he said "Newton discovered the spectrum exactly 300 years before England won the World Cup!"   Indeed he did.   The old pound note showed Newton with a small triangular prism he had bought at Stourbridge Fair.  It is just underneath his reflector telescope (which he invented).   The existence of the spectrum had been known for thousands of years but it was thought that light was being changed by the glass.   Newton came up with experiments which split light into the spectrum and then reassembled it back into white light.   He also demonstrated that pure colours in the spectrum could not be changed into any other.

1800

William Herschel discovered the planet Uranus and heat rays.   He was interested in what portion of the spectrum carried heat from the Sun to Earth.   He set up an experiment that used a row of thermometers ( that he had made himself).   He moved the thermometers through the spectrum and saw a slight rise from blue to red.   What was amazing was that when the thermometers were moved out of the light and into  the dark region beneath red, the thermometers shot up.    He had discovered what he called 'heat rays'.   Later the term infrared was used to describe them - infra is Latin for beneath.    

1801

Johann Wilhelm Ritter invented the dry cell battery and showed that galvanising protected iron from rusting by an electrochemical effect.   Ritter was also interested in the chemical reactions of silver chloride which breaks down to black silver when it is exposed to light.   He heard about Herschel's experiment and probably thought that  heat rays could be responsible for the reaction.   After all, many reactions happen when you heat them up.   But Ritter found that the reaction didn't happen at all at the red end of the spectrum.   As he moved the silver chloride towards the violet end it darkened slightly.   But when he moved the chemical into the darkness beyond violet it reacted quickly.   Ritter had extended the spectrum again but this time at the other end.   Ritter called the rays 'chemical rays' but this was later changed to ultraviolet - ultra is Latin for beyond.

1860

In 1860 the Scottish physicist James Clerk Maxwell used some very clever calculations to show that light was made of intertwined waves of electric and magnetic fields - electromagnetic waves.   He was also able to predict that there were waves longer than the infrared waves found by the astronomer William Herschel

1888

The German physicist Heinrich Hertz set out to create Maxwell's predicted electromagnetic waves.   In 1888  he managed to send a signal across his lab.      Basically what he did was to make a machine that created an electric spark which switched on and off many times a second.   On the other side of his lab he had a simple coil of wire with a tiny gap in it.     When his spark machine was switched on, the coil on the other side of the lab also had a tiny spark in its gap.   Something invisible was jumping across the room and transferring energy.   Hertz had made and received radio waves.

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1895

On 5 November 1895 , The German physicist  Wilhelm Konrad Roentgen was working in his lab with something called a cathode ray tube.   It's a device a bit like a television tube.   He darkened his lab, turned  on the tube and was startled to see a chemical on the other side of his lab glow.   He turned off the tube and the chemical stopped glowing.  He turned the tube back on and the chemical started glowing again.   He put a cardboard box over the tube.   The chemical still glowed.   He took the chemical to the next room and shut the door.   It still glowed when the tube was on.   He had discovered a new type of invisible rays.   But unlike all of the others these could go through the door of his lab.   He had no idea what they were, so he called them X rays.   As Roentgen's name is so difficult to pronounce (unless you are German) an attempt to name the rays after their discoverer failed.   That's why everybody still calls them by their 'temporary' name.

In 1899, Hermanus Haga and C. H. Wind found some evidence for X rays being waves, but is was not until 1912 that Max Von Laue came up with conclusive evidence that they were waves.

1900

In 1900 the French physicist Paul Villard. discovered that some radioactive chemicals emitted rays that were much more penetrating than X rays.   In 1914 Ernest Rutherford showed that the rays that Villard had discovered were a type of EM wave of a shorter wavelength than X rays.  Rutherford decided to call them Gamma Rays (the third letter of the Greek alphabet) as they were the third type of radiation to be detected from radioactive elements.   With this discovery the electromagnetic spectrum was complete.

The Infrared Processing and Analysis Center

Click on their logo for details of Herschel's and Ritter's experiments  and how to have a go at them yourself.