In the same section Boltzmann also addressed and explained the negative pressures which some liquid metastable states exhibit (for example T r = 0.8 of Fig. 1). He concluded that such liquid states of tensile stresses were real, as did Tien and Lienhard many years later who wrote "The van der Waals equation predicts that at low temperatures liquids sustain enormous tension...In recent years measurements have been made that reveal this to be entirely correct."