  It is well known that, in contrast to general relativity, there are two
conformally related frames, the Jordan frame and the Einstein frame, in which
the Brans-Dicke theory, a prototype of generic scalar-tensor theory, can be
formulated. There is a long standing debate on the physical equivalence of the
formulations in these two different frames. It is shown here that gravitational
deflection of light to second order accuracy may observationally distinguish
the two versions of the Brans-Dicke theory.
