IN WHAT PEOGEESS CONSISTS. 3 



IS the api^earance of a difference between two parts of this 

 substance ; or, as the phenomenon is called in physiological 

 language, a differentiation. Each of these differentiated 

 divisions presently begins itself to exhibit some contrast of 

 parts ; and by and by these secondary differentiations be- 

 come as definite as the original one. This process is con* 

 tinv.ously repeated — is simultaneously going on in all parts 

 of the growing embryo ; and by endless such differentia- 

 tions there is finally produced that complex combination of 

 tissues and organs constituting the adult animal or plant. 

 This is the history of all organisms whatever. It is settled 

 beyond dispute that organic progress consists in a change 

 from the homogeneous to the heterogeneous. 



Now, w^e propose in the first place to show, that this 

 law of organic progress is the law of all progress. Whether 

 it be in the development of the Earth, in the development 

 of Life upon its surface, in the development of Society, of 

 Government, of Manufactures, of Commerce, of Language, 

 Literature, Science, Art, this same evolution of the simple 

 i-nto the complex, through successive differentiations, holds 

 throughout. From the earliest traceable cosmical changes 

 down to the latest results of civilization, we shall find that 

 the transformation of the homogeneous into the heteroge- 

 neous, is that in which Progress essentially consists. 



With the view of showing that if the Nebular Hypoth- 

 esis be true, the genesis of the solar system supplies one 

 illustration of this law, let us assume that the matter of 

 which the sun and j^lanets consist was once in a diffused 

 form ; and that from the gravitation of its atoms there 

 resulted a gradual concentration. By the hypothesis, the 

 solar system in its nascent' state existed as an indefinitely 

 extended and nearly homogeneous medium — a medium 

 almost homogeneous in density, in temperature, and in 

 otlier physical attributes. The first advance towards con- 

 solidation resulted in a differentiation between the occupied 



