(98.)

The fixed relations which exist between the temperatures of common steam and its pressure and density, have never been discovered from any general physical principles. The pressures and the densities however, which correspond to a great variety of temperatures throughout the thermometric scale, have been ascertained by extensive series of experiments instituted by philosophers of this and other countries. From a comparison of the temperatures and pressures thus found by experiment, empirical formulæ have been constructed, which exhibit, with an approximation sufficiently close for practice, this relation; and these formulæ may accordingly be used for the computation of tables exhibiting the pressures, temperatures, and densities of common steam; and such tables will have sufficient numerical accuracy for all practical purposes. These formulæ, and the tables resulting from them, will be found in the Appendix to this volume.