As we may judge of the uniformity of temperature from the unaltered
time of vibration of a pendulum, so we may also learn from the
unaltered rotatory velocity of the earth the amount of stability in the
mean temperature of our globe. This is the result of one of the most
brilliant applications of the knowledge we had long possessed of the
movement of the heavens to the thermic condition of our planet. The
rotatory velocity of the earth depends on its volume; and since, by the
gradual cooling of the mass by radiation, the axis of rotation would
become shorter, the rotatory velocity would necessarily increase, and
the length of the day diminish with a decrease of the temperature. From
the comparison of the secular inequalities in the motions of the moon
with the eclipses observed in former ages, it follows that, since the
time of Hipparchus,--that is, for full 2000 years,--the length of the
day has certainly not diminished by the hundredth part of a second. The
decrease of the mean heat of the globe during a period of 2000 years
has not therefore, taking the extremest limits, diminished as much as
1/306th of a degree of Fahrenheit.[42]--_Humboldt’s Cosmos_, vol. i.