is the angle between the original direction of the beam and the direction at which the scattered waves come to the measuring apparatus.
Compton then tested this relation experimentally,[190] using as his incident waves the characteristic
-rays from a molybdenum target, and as his scattering substance the free (or substantially free) electrons found in graphite. He found indeed that the
-line of molybdenum was shifted toward longer wave-lengths just as predicted, and in approximately the correct amount. There was also an unshifted line presumably due to scattering by bound electrons.
Compton had used an ionization-chamber spectrometer for locating his lines. Ross[191] repeated these experiments at Stanford University, California, using the more accurate photographic plate for locating his lines, but still using graphite as the scattering substance. His published photograph shows a line shifted the correct amount and also an unshifted one, but he commented on the fact that the shifted line shows no sign of a separation of the
and