A pair of particles makes a fog spot as they pass through the wet air of a "cloud chamber"

The first photograph showing the creation of a pair of particles, revealed by the fog spots they make in passing through the wet air of a "cloud chamber." The two particles, curving apart under the influence of a magnet, were created in the annihilation of a particle of light (coming invisibly from below).

This photograph not only shows the conversion of energy to mass, but confirms Einstein's idea that a light-particle will yield up its quantum of energy all at once in a single burst.

Image © Archives Curie et Joliot-Curie, Paris.
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