  We investigate the energetics of the jet and X-ray corona of Cyg X-1. We show
that the current estimates of the jet power obtained from Halpha and [O III]
measurements of the optical nebula surrounding the X-ray source allow one to
constrain the bulk velocity of the jet. It is definitely relativistic (v >0.1c)
and most probably in the range (0.3-0.8)c. The exact value of the velocity
depends on the accretion efficiency. These constraints are obtained
independently of, and are consistent with, previous estimates of the jet bulk
velocity based on radio measurements. We then show that the X-ray emission does
not originate in the jet. Indeed, the energy budget does not allow the corona
to be ejected to infinity at relativistic speed. Rather, either a small
fraction of the corona escapes to infinity, or the ejection velocity of the
corona is vanishingly low. Although the corona could constitute the jet
launching region, it cannot be identified with the jet itself. We discuss the
consequences for various X-ray emission models.
