THE REIGN OF UNIVERSAL WINTER. 403 



to perpetuity, is but a passing phase ; and when we shall 

 have passed away with the other transient existences 

 around us, some succeeding intelligence, gifted with the 

 power to travel from sphere to sphere, will note the world 

 in an altered condition. 



I step here upon ground which has been somewhat con- 

 tested. It was long since alleged that if our world be still 

 in process of refrigeration, a sensible reduction in temper- 

 ature ought to have taken place in 2000 years. But no 

 such reduction has been satisfactorily established, though it 

 will be confessed that we scarcely have exact observations 

 on temperature which are more than two hundred years 

 old. It was also alleged that since a reduction of temper- 

 ature must be accompanied hj a reduction of volume, the 

 rate of the earth's rotation upon its axis must have been 

 accelerated. But Laplace has demonstrated from ancient 

 observations on eclipses that the mean day has not been 

 diminished -g-g-g-th of a second since the time of Hipparchus, 

 or during an interval of 2500 years. These negative re- 

 sults have been opposed to the theory of Cordier in refer- 

 ence to the former high temperature of the earth, and it 

 has, till recently, been customary to sjDeak of the thermal, no 

 less than the astronomical conditions of our planet as con- 

 stant. Poisson, an eminent French mathematician, proved, 

 as was supposed, that the heat escaping from the earth in 

 the latitude of Paris was only sufficient to elevate the tem- 

 perature of a column of water eighteen inches high the tri- 

 fling amount of one degree and a half. Vogt, a celebrated 

 German geologist, affirms that the existing temperature of 

 the surface of the earth is but one twelfth of a degree 

 higher than it would be if the earth were completely cooled 

 to the core. According to the later researches of Pouillet, 

 the heat communicated to the surface of the earth from the 

 central fire is but one fortieth the amount received from 



