If the surface of the Earth consisted of one and the same homogeneous fluid mass, or of strata of rock having the same color, density, smoothness, and power of absorbing heat from the solar rays, and of radiating it in a similar manner through the atmosphere, the isothermal, Isotheral, and isochimenal lines would all be parallel to the equator.
"COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1"
Alexander von Humboldt
90-109. Since we have acquired a more accurate knowledge of the true relations of the distribution of heat on the surface of the earth, that is to say, of the inflections of isothermal and Isotheral lines, and their unequal distance apart in the different eastern and western systems of temperature in Asia, Central Europe, and North America, we can no longer ask the general question, what fraction of the mean annual or summer temperature corresponds to the difference of one degree of geographical latitude, taken in the same meridian?
"COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1"
Alexander von Humboldt