50 LIMITS AND METHOD OF THE 



liquid surface of our planet. It might be said, according to 

 a fine expression of Lavoisier, that the marvel of the an- 

 cient mythus of Prometheus is incessantly renewed before 

 our eyes. 



When we apply the course which it is proposed to follow 

 in the exposition of the physical description of the earth, to 

 the sidereal part of the science of the Cosmos, or to the 

 description of what is known to us of the regions of space, 

 and of the heavenly bodies which they contain, we shall 

 find our task remarkably simplified. If, according to an- 

 cient but inexact forms of nomenclature, we distinguish 

 between physics, or the general consideration of matter, its 

 forces, and its movements, and chemistry, or the conside- 

 ration of the different nature of substances, their elementary 

 composition, and their attractions not depending on rela- 

 tions of mass or the laws of gravitation, we must of course 

 recognise that the telluric portion of our study embraces 

 both physical a-nd chemical processes. By the side of the 

 fundamental force of gravitation, we discover around us on 

 the earth the action of other forces, taking effect either 

 when the particles of matter are in contact, or at exceedingly 

 small distances apart ( 22 ) ; to which forces we give the name of 

 chemical affinity. Under various modifications, by electri- 

 city, by heat, by condensation in porous bodies, or by the 

 contact of an intermediate substance, these forces are inces- 

 santly in action in inorganic matter, and in the tissues of 

 animals and plants. But, in the regions of space, we are 

 only cognizant by direct observation of physical phenomena, 

 and among these (excepting in the case of the small aste- 

 roids, which appear to us under the form of aerolites or 

 shooting stars,) we know with certaiiity only those effects 



