The “Isothermal Layer”

Abstract

I AM inclined to doubt whether Commander Hepworth's suggestion (NATURE, January 25) that the so-called isothermal layer is simply due to radiation from the material, solid or gaseous, which circulates round the sun with an orbital motion and gives rise to the zodiacal light, can be reconciled with the configuration of the surfaces of equal temperature in the upper air which show a progressive increase of temperature from low to high latitudes. It seems more probable that this increase, and the fact that above a certain height in these latitudes the temperature no longer diminishes with the altitude, are the result of the prevalent movement, outside the equatorial belt, of the higher portion of the atmosphere from west to east with comparatively great velocity, which increases with the latitude and altitude, and extends to lower levels as the distance from the equator becomes greater. This movement, which gives the upper atmosphere greater angular velocity than the lower and the earth beneath, partially counteracts the force of gravity and causes the air to rise and expand without doing work, and therefore without suffering a decrease in temperature. At the equator there appears to be no satisfactory evidence of an “isothermal layer”.