12 - INTRODUCTION. 



hydrogen, sulphur, potash, phosphorus, tin, &c.), and the 

 degree of their tendency to combine, or their chemical 

 affinity. Differences of form and composition are, however, 

 I here repeat, the elements of the whole of our knowledge 

 of matter ; they are the abstractions under or through which, 

 by means of measurement and analysis, we endeavour to 

 comprehend the whole of the material world. The detonation 

 of fulminates with a slight mechanical pressure, and the 

 still more violent explosion, accompanied by fire, of chloride 

 of nitrogen, contrast with the explosive combination of 

 chlorine and hydrogen gas on exposure to the direct inci- 

 dence of a solar ray, more especially the violet ray. Change 

 of substance, combination and decomposition, mark the 

 perpetual circuit of the elements in inorganic nature, as 

 well as in the animated cells of plants and animals. " The 

 quantity of the existing substances, however, remains the 

 same ; the elements only change their relative positions/' 



Thus the sentence anciently enounced by Anaxagoras, 

 still holds good, that " that which exists in the universe 

 suffers neither augmentation nor decrease " and that what 

 his contemporaries termed the perishing of things, was a 

 mere dissolution of previous combinations. It is indeed 

 true that the terrestrial sphere, inasmuch as it is the seat of 

 the only organic corporeal world accessible to our observa- 

 tion, appears a continual field of death and of corruption ; 

 but it is also true, that the great natural process of slow 

 combustion, which we term corruption, does not bring with 

 it any annihilation. The disengaged substances recombine 

 in other forms, which, by the forces residing in them, 

 become the means of calling forth fresh life from the bosom 

 of the earth. 



