Laue in his very first experiments used white radiation of all possible
wavelengths and allowed this radiation to fall on a stationary crystal. The
crystal diffracted the X-ray beam and produced a very beautiful pattern
of spots which conformed exactly with the internal symmetry of the
crystal. Let us analyse the experiment with the aid of the Bragg equation.
The crystal was fixed in position relative to the X-ray beam, thus not only
was the value for *d* fixed, but the value of was also fixed
(see Fig. 20).

The only possible variables therefore are the integer *n* and wavelength
, with the result that in the Laue photograph each observed reflection
corresponds to the first order of reflection of a certain wavelength, the
second order of half the wavelength and a third order of a third of the
wavelength, and so on. The Laue photograph which is obtained from a
single crystal is simply a stereographic projection of the planes of the
crystal.

**Copyright © 1981, 1997 International Union of Crystallography**