David Harriman is not the only working physicist to blunder about orbital mechanics. It is an easy error to say that the path of a projectile is a parabola (p 50). Attempting to explain the development of the atomic theory, Harriman offers an erroneous simile comparing a hydraulic pump to a lever (pp 123-124).Consider the allusions to elastic and inelastic collisions. “… [Newton] deliberately varied the mass of the bobs and thereby proved that his law applied to both elastic and inelastic collisions.” (127) Referring again to Sears and Zemansky (sec 8-3; pp 148-151), in a perfectly inelastic collision the two bodies stick together, their kinetic energies before and after are not conserved, and the difference lost is converted to heat. I believe that here Harriman is using the word “elastic” in its vernacular sense: balls of yarn or wood were deformed more or less by the impacts, having negligible consequences to the experiment. However, discussing the kinetic theory of gases, Harriman uses elastic and inelastic in their proper technical senses (p 166).