By the last decade of the 19th century,
scientists were feeling confident
about their understanding
of Maxwell's electromagnetic spectrum,
electromagnetic waves of various lengths, or frequencies,
that traveled at the speed of light.
On the long end of the spectrum were radio waves
that were used to transmit sound from point to point;
microwaves, used today in cooking with microwave ovens;
and infrared waves, waves that were
originally discovered in 1800 by Herschel
when he measured the temperature of the colors split by a prism
and found that the highest temperature
was an area of invisible light next to the red wavelength.
They also knew that visible light formed
the smallest group of frequencies.
It was followed by the ultraviolet light frequencies
that tan our skins
and cause various chemicals to fluoresce.
Then two discoveries shook late 19th-century scientists
out of their complacency.
On November 8, 1895,
a German physicist, Wilhelm Roentgen,
was experimenting with a cathode ray tube,
a kind of vacuum tube and the basis
of every television and computer screen today.
These tubes worked by having a negative and positive terminal
inside an evacuated glass container
so that when a high-voltage current
was passed through the tube,
a beam was produced called a cathode ray.
Like many others at the time, Roentgen was investigating
the nature and properties of this curious beam,
one of which was that the range of a cathode ray was short,
just a few inches.
So it was with some surprise
that he saw a phosphorescent material
on the other side of the room light up
when the beam was initiated,
especially since his tube was encased in cardboard.
A few days later, in what must have been a wonder,
Roentgen held his hand between the tube and the screen
and saw his bones.
Then on the 22nd of December, he made the first radiograph
of his wife's hand, wedding ring and all.
Roentgen had discovered a new short high-frequency form
of electromagnetic radiation.
He had discovered X-rays
and a way to look inside the body of an animal.
At the time, X-rays appeared to many like black magic,
but over the next century,
X-rays would prove invaluable in medicine
and in unlocking the secrets of crystal structures.
The next year, 1896, would bring an equally surprising discovery.
French physicist Antoine-Henri Becquerel believed
that X-rays were produced by phosphorescent compounds,
and he set about to test his theory.
Becquerel took phosphorescent compounds,
placed them on a photographic plate
wrapped in black paper, and set them in the sun.
Knowing that the X-rays would pass through the paper,
he hoped to see their telltale signatures
when the plates were processed.
Moving from specimen to specimen,
his next sample was uranium potassium sulfate,
but the day was cloudy,
so he simply stored it with a photographic plate
in a drawer for a number of days.
Then, for some curious reason,
he processed that photographic plate.
And to his surprise, the plate was exposed.
Somehow, the uranium was giving off
a new kind penetrating ray.
Building on Becquerel's results,
Polish chemist Marie Curie found that this property,
which she called radioactivity,
was common to uranium and thorium,
two naturally occurring elements.
Curie also found that the kind of rock called pitchblende
was even more radioactive.
Immediately, she and her husband went to work
refining tons a pitchblende ore
and, in 1898, announced to the world
the discovery of two new radioactive elements,
polonium and radium.
Radium was so radioactive,
it was used to light up watch dials in the dark.
In fact, it is the most radioactive
of all naturally occurring elements.
Later, physicists would determine
there are three forms of radioactivity:
alpha particles;
beta rays, which are actually particles;
and gamma rays, the highest energy wave
on the electromagnetic spectrum.
Unfortunately, Marie Curie and her husband
received lethal doses of radiation during their work.
Radioactivity proved to be both a tremendous servant
for humankind's benefit
and a dangerous element for its destruction.