Mysteries of vernacular:
X-ray,
a form of electromagnetic radiation
capable of penetrating solids.
The word X-ray harkens back
to the work of Rene Descartes,
a French philosopher,
mathematician,
and writer in the 17th century.
One of Descartes innumerable contributions
to the world of numbers
was the invention of a simple yet brilliant convention
most people take for granted today:
the representation of unknowns
within an equation as X, Y, and Z.
When the German scientist Wilhelm Rontgen
discovered what we now call X-rays
in the late 19th century,
he gave them the name X-strahlen.
Strahlen is German for shine,
and X, of course, represented the unknown nature
of the radiation Rontgen had discovered,
the X-factor, so to speak.
The English translation maintained the X
but replaced the German shine with ray,
meaning a beam of light.
Coincidentally, in mathematics,
the word ray refers to a line
with a point of origin that has no end
and extends to infinity,
bringing us neatly back to the unknown.
Today we understand what X-radiation is,
and in spite of the humble objections
of its discoverer,
it is also commonly called Rontgen Radiation,
eliminating with the X
the fundamental mystery of its nature.