This is shown by the isotherm for -4.5, which surrounds the point Q, the melting point of the ternary salt.
isotherm, a compound of two Greek words meaning equal temperature, is the name given in meteorology to such lines as this.
The scale must, however, be laid perpendicularly to the isotherm, as before.
Draw an isotherm east and west across the map, through your station.
Beyond the isotherm of 50 for the warmest month forest trees and cereals do not grow.
Draw through your station an isotherm inclined from northeast to southwest.
The January isotherm of 15 F. skirts its northern shore; that of 40 crosses its southern border.
The southern limit of its distribution approximates the isotherm of forty-five degrees.
On a second blank weather map draw an isotherm through your station inclined from northwest to southeast.
The polar limits of the temperate zones are fixed by the isotherm of 50 for the warmest month.