Reply to Comment on "Failure of the work-Hamiltonian connection for   free-energy calculations" by Horowitz and Jarzynski
  We show that the Comment [arXiv:0808.1224] by Horowitz and Jarzynski obtains as a main result a general free energy change for a harmonic system that in the macroscopic limit does not recover the textbook expression for the energy change of a Hookean spring. The reason is that Horowitz and Jarzynski improperly identify work with parametric changes of the Hamiltonian instead of with the standard quantity, force times displacement. 
J.M.G. Vilar and J.M. Rubi