New Monte Carlo Technique for Studying Phase Transitions. ALAN M. FERRENBERG and ROBERT H. SWENDSEN [Phys. Rev. Lett. 61, 2635 (1988].A reference to the work of I. R. McDonald and K. Singer [Discuss. Faraday Soc. 43, 40 (1967)] was inadvertently omitted. They were, to the best of our knowledge, the first to use the equations of Salsburg et al [J. Chem. Phys. 30, 65 (1959)] to evaluate physical quantities over a range of temperatures.It has also been called to our attention that the extension of the histogram approach to complex temperatures, which we attributed to Bhanot and co-workers, was actually introduced earlier by M. Falcioni, E. Marinari, M. L. Paciello, G. Parisi, and B. Taglienti [Phys. Lett. 108B, 331 (1982)], and E. Marinari [Nucl. Phys. B235 [FS11], 123 (1984)]. Constraint on Deviations from Universality in the Coupling to Gravity of Photons and High-Energy Cosmic Rays. M. GASPERINI [Phys. Rev. Lett. 62, 1945 (1989)]. I would like to call attention to previous related work. It has been pointed out by M. D. Gabriel and M. P. Haugan that very stringent constraints on universality of the gravitational coupling, similar to the one presented in my paper, based, however, on tests of the isotropy of space, are contained in M. P. Haugan and C. M. Will, Phys. Today 40, No. 1, 69 (1987); P. Lubin et al, Astrophys. J. 298, LI (1985); J. D. Prestage et al, Phys. Rev. Lett. 54, 2398Lett. 54, (1985, and their theoretical interpretation was developed in V. W. Hughes et al, Phys. Rev. Lett. 4, 342 (1960); M. P. Haugan, Ann. Phys. (N.Y.) 118, 156 (1979). Finally, the possibility of gravityinduced Cherenkov emission, in the case of violation of the equivalence principle, was first considered in E. F. Beall, Phys. Rev. Lett. 21, 1364 (1968 Phys. Rev. D 1, 961 (1970). (This last information was kindly provided to me by T. J. Devlin.)
