/ ZO TRANSACTIONS OF THE AMERICAN INSTITUTE. 



apparent on any clear night when the clouds do not reflect the 

 heat rays back again to the earth. Are not the sun and fixed stars 

 constantly radiating enormous c|uantities of heat and light into 

 space ? Whether force can exist independently of matter, is a 

 debatable question, but even if it cannot, then we have the etlier, 

 a material medium, the existence of which is supposed necessary 

 to account for the transmission of forces across otherwise vacant 

 spaces. This supposed ether has the property of receiving heat 

 and other radiations, and of transmitting them indefinitely, or until 

 they are absorlied by some grosser matter. 



Whether the substances of which the interior mass of the earth 

 is composed, diminish or increase in density when they undergo 

 solidification, is, I believe, not a matter of certainty; but at any 

 rate the difierence in specific gravity would seem to be too slight 

 to counterbalance the immense difiTerence in the rate of cooling 

 between the surface and interior. Convection could not possibly 

 take plac^e with suiiicient rapidity to overcome this difference, 

 when the entire mass had, in cooling, approached the solidifying 

 point of temperature, and a crust. must be formed as on the sur- 

 face of lava streams, whose strength need ^ot be very great to 

 sustain itself. 



Among the geological evidences which have been supposed "to 

 indicate the liquidity of the earth's interior, are included the regu- 

 larly increasing temperature of the earth downwards, the great 

 number of active and extinct volcanoes, the constant gradual ele- 

 vation and depression of continents and ocean beds, the connec- 

 tion of volcanic eruptions with earthquakes extending over districts 

 which comprise considerable portions of the earth's surface, the 

 fcrms and directions of long mountain ranges presenting exactly 

 such an appearance as might be expected in the solid crust of a 

 liquid earth, which by a slight contraction within had made the 

 shell too large, so that by its own weight, upward and lateral 

 pressure would be gradually produced, causing ridges and fold- 

 ings of the crust, corresponding somewhat in general appearance 

 to the shrivelled skin of a shrunken apple. 



Mr. Wood attributes all or nearly all these phenomenas to the 

 mysterious influence of a great unknown central orb, which in 

 some manner analogous to that of the moon in causing tides, and 

 of the sun in modifying ocean currents, produces elevations and 

 depressions in the solid earth, from which, by some means not well 

 explained, the other different results are developed. Now the 



