\R["o]ntgen ray\ (Physics)
Any of the rays produced when cathode rays strike upon
surface of a solid (as the wall of the vacuum tube).
R["o]ntgen rays are noted for their penetration of many
opaque substances, as wood and flesh, their action on
photographic plates, and their fluorescent effects. They were
called {X rays} by their discoverer, W. K. R["o]ntgen. They
also ionize gases, but cannot be reflected, or polarized, or
deflected by a magnetic field. They are regarded as
nonperiodic, transverse pulses in the ether. They are used in
examining opaque objects, as for locating fractures or
bullets in the human body.