May 14, 2026 · 20 min · 8 segments
In 1895, German physicist Wilhelm Conrad Röntgen discovered a new type of radiation. It was invisible and penetrating to some materials, but not others. He called the radiation "X-rays," and the…
Antoine-Henri Becquerel was born in 1852 into a family where science was practically an inheritance.
His grandfather, Antoine César Becquerel, was a pioneer in the study of luminescence.
His father, Edmond Becquerel, discovered both the photovoltaic effect and thermionic emission.
The entire environment Henri grew up in pointed him along a path towards physics.
He was raised in Paris, studied there, and obtained his doctorate in 1888 from the University of Paris with a thesis on the plane polarization of light with the phenomena of phosphorescence and absorption of light by crystals.
Eventually, Becquerel moved beyond his family name and became a respected scientist in his own right, especially in the study of light, crystals, and electrical phenomena.
By the 1890s, he was already established as a prominent physicist at the Muséum National d'Histoire Naturelle.
When Wilhelm Roentgen announced his discovery of X-rays in 1895, scientists across the world were stunned.
Here was a new kind of invisible radiation that could pass through solid objects and produce photographic images.
Becquerel was among those fascinated by the new phenomenon, and like many others, he began wondering whether there might be a connection between X-rays and other forms of light.
He was especially interested in phosphorescence, the kind of glow some materials give off after being exposed to sunlight.
He knew from prior experience that certain uranium compounds, especially phosphorescent ones, might possibly produce X-rays of their own since the phosphorescent glass at the end of a cathode ray does the same.
So, he designed an experiment as follows.
He exposed uranium salts to the sun for long periods of time and wrapped photographic plates in black paper to block out visible and UV light.
Then, he placed the uranium salts on top of the plates and observed whether the plates were exposed through the paper.
If the uranium salt produced X-rays, a shadow image of the uranium would show up on the developed plates.
When he unwrapped the plates, he did in fact find shadows of the uranium salts embedded into them, seemingly confirming Becquerel's theory that phosphorescent materials produce X-rays.
At first, this setup seemed like a promising experiment.
However, it served more so as a red herring, leading Henri on a path towards a link between sunlight, phosphorescence, and X-rays.
He reported his results at the French Academy of Sciences meeting on February 24, 1896.
Becquerel immediately wanted to continue his experiments with uranium salts and sunlight, but unfortunately the weather was overcast for the next several consecutive days.
So, waiting out the weather, Henri placed the uranium salts and photographic plates in a drawer to wait for the next opportunity.
There wasn't another sunny day until March 1st, about a week later, and when that day came, Henri took his salts and paper covered plates back out of the drawer.
But, instead of beginning his experiments right away, Henri decided to develop the plates that were sitting in the drawer during the few days.
Why he did this is still unknown.
Antoine-Henri Becquerel was born in 1852 into a family where science was practically an inheritance.
His grandfather, Antoine César Becquerel, was a pioneer in the study of luminescence.
His father, Edmond Becquerel, discovered both the photovoltaic effect and thermionic emission.
The entire environment Henri grew up in pointed him along a path towards physics.
He was raised in Paris, studied there, and obtained his doctorate in 1888 from the University of Paris with a thesis on the plane polarization of light with the phenomena of phosphorescence and absorption of light by crystals.
Eventually, Becquerel moved beyond his family name and became a respected scientist in his own right, especially in the study of light, crystals, and electrical phenomena.
By the 1890s, he was already established as a prominent physicist at the Muséum National d'Histoire Naturelle.
When Wilhelm Roentgen announced his discovery of X-rays in 1895, scientists across the world were stunned.
Here was a new kind of invisible radiation that could pass through solid objects and produce photographic images.
Becquerel was among those fascinated by the new phenomenon, and like many others, he began wondering whether there might be a connection between X-rays and other forms of light.
He was especially interested in phosphorescence, the kind of glow some materials give off after being exposed to sunlight.
He knew from prior experience that certain uranium compounds, especially phosphorescent ones, might possibly produce X-rays of their own since the phosphorescent glass at the end of a cathode ray does the same.
So, he designed an experiment as follows.
He exposed uranium salts to the sun for long periods of time and wrapped photographic plates in black paper to block out visible and UV light.
Then, he placed the uranium salts on top of the plates and observed whether the plates were exposed through the paper.
If the uranium salt produced X-rays, a shadow image of the uranium would show up on the developed plates.
When he unwrapped the plates, he did in fact find shadows of the uranium salts embedded into them, seemingly confirming Becquerel's theory that phosphorescent materials produce X-rays.
At first, this setup seemed like a promising experiment.
However, it served more so as a red herring, leading Henri on a path towards a link between sunlight, phosphorescence, and X-rays.
He reported his results at the French Academy of Sciences meeting on February 24, 1896.
Becquerel immediately wanted to continue his experiments with uranium salts and sunlight, but unfortunately the weather was overcast for the next several consecutive days.
So, waiting out the weather, Henri placed the uranium salts and photographic plates in a drawer to wait for the next opportunity.
There wasn't another sunny day until March 1st, about a week later, and when that day came, Henri took his salts and paper covered plates back out of the drawer.
But, instead of beginning his experiments right away, Henri decided to develop the plates that were sitting in the drawer during the few days.
Why he did this is still unknown.
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