  I suggest that measurements of intensity fluctuations caused by classical
wave interactions can be used to find unresolved gravitational lenses and
determine time delays of essentially arbitrary length among the images formed
by a gravitational lens. No interferometry i s needed, the time delays can be
measured by analyzing the intensity signal alone. The technique works with
lensed sources that have constant luminosities and is capable of measuring very
long time delays. I suggest interferometric techniques, capable of measuring
time delays of arbitrary length, that can be used to refine the measurements.
