. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 392 RECORD OF SCIENCE FOR 1887 AND 1888. airs are being mixed with warm and moist; on the other hand aqueous vapor with hiteut heat is being added to the air by evaporation from the ground, and again being taken from the air, but leaving its heat behind by the process of formation of rain, hail, and snow. Therefore the ascent and descent of atmospheric currents is by no means an adia- batic process, and it is the aim of Bezold to so present
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 392 RECORD OF SCIENCE FOR 1887 AND 1888. airs are being mixed with warm and moist; on the other hand aqueous vapor with hiteut heat is being added to the air by evaporation from the ground, and again being taken from the air, but leaving its heat behind by the process of formation of rain, hail, and snow. Therefore the ascent and descent of atmospheric currents is by no means an adia- batic process, and it is the aim of Bezold to so present graphically the changes that take place in ascending and descending air as that we may at any time calculate its thermal condition. (27) Bezold.—The original memoirs of Hertz and Bezold detailing their graphic methods in tbermo-dynamics as applied to our atmosphere will be given in full in the promised collection of translations. The ground covered by these will be easily understood from the following analysis of Bezold's work by Lettry,* with slight additions by myself. (A.) DEFINITIONS.—Let ji aud v be respectively the values of the vol- ume and pressure of a unit weight, namely, a unit mass, of gas or gas- eous vapor whose absolute temperature is T. Then according to the law of Boyle Mariotte-Gay-Lussac aud Charles, we have pv=IiT (a). Let the condition of the unit of gas be graphically represented as to pressure aud volume by the ordinate and abscissa of a point; when p and V are given, the location of the point is known by the graphic con- struction, but equally is the temperature/! known by the equation {a); thus the location of a point in the diagram corresponds to a definite temperature of the gas. If the gaseous mass is maintained at a con- stant temperature then p aud v may vary continuousl3^, only fulfilling the condition that their product p v remains constant. The locus of the continuous series of points thus defined is called an isotherm, and we see that the
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