What is "isothermal zones"

Isothermal \I`so*ther"mal\, a. [Cf. F. isotherme.]

1. Relating to equality of temperature, or an isotherm.

2. (Phys. Geog.) Having reference to the geographical distribution of temperature, as exhibited by means of isotherms; as, an isothermal line; an isothermal chart. Isothermal line.

   1. An isotherm.

   2. A line drawn on a diagram of energy such that its ordinates represent the pressures of a substance corresponding to various volumes, while the absolute temperature is maintained at a constant value.

      Isothermal zones, spaces on opposite sides of the equator having the same mean temperature, and bounded by corresponding isothermal lines.