The ion composition experiment on ISEE 3 obtains the velocity distributions for 4He++, completely separated from protons. Temperatures and velocities derived from these distributions have been compared with the Los Alamos National Laboratory proton temperatures and velocities obtained from the National Space Science Data Center. The results, which apply on the macroscale, confirm and extend previous observations and show the following: (1) The temperature ratio T&agr;/Tp drops with increasing transit time R/V. This indicates that interactions among the ions take place, but it does not identify the collision mechanism. (2) At low &tgr;e/&tgr;c (the ratio solar wind expansion time/collision time) the temperatures of the individual species are proportional to their mass. As &tgr;e/&tgr;c increases, the He temperature drops, and the H temperature increases to a common intermediate value determined by equipartition of energy. (3) T&agr;/Tp is approximately proportional to (mp Tp +m&agr;T&agr;)/ (m&agr;+mp), as suggested for Coulomb collisions. The temperature ratio is more sensitive to the prevailing value of T than to that of the density N. Thus the scattering depends more strongly on the thermal speed than on the interparticle separation. (4) The state of ion equilibrium is determined by the value of &tgr;e/&tgr;c, independent of the type of flow. (5) As &tgr;e/&tgr;c increases from 0.01 to unity and above, the temperature ratio first remains constant near 4, then drops uniformly to unity, and remains constant for &tgr;e/&tgr;c >1. The relative velocity difference ‖V&agr; -Vp‖/ VA decreases monotonically to zero as a function of &tgr;e/ &tgr;s, whee &tgr;s is the slowing down time due to collisions. The evidence establishes Coulomb collisions as the important ion-ion equilibrating process in the solar wind when the temperature is low.