  A low-temperature scanning tunneling microscope is employed to build a
junction comprising a Co atom bridging a copper-coated tip and a Cu(100)
surface. An Abrikosov-Suhl-Kondo resonance is evidenced in the differential
conductance and its width is shown to vary exponentially with the ballistic
conductance regardless of the tip structure. Using a theoretical description
based on the Anderson model, we show that the Kondo effect and the conductance
are related through the atomic relaxations affecting the environment of the Co
atom.
