The consequences of the interaction of incoming solar wind protons with particles reflected at the bow shock have been studied with Heos 1 plasma and magnetic field data. The proton bulk speed has been found to decrease by 30 km/s in the region where upstream waves are observed. The wave amplitude has been found to increase with increasing bulk speed, on average, by the relation ΔB=0.28+8.5 ¿10-3Vsw, where B is in gammas and Vsw is in kilometers per second. The wave amplitude has also been found to decrease with increasing proton number density. Agreement with Barnes' (1970) theoretical prediction of the ΔB-Np relation is achieved only if the assumption of a constant number density of reflected protons is made.