530 TEE POPULAR SCIENCE MONTHLY. 



greater or less number of wholly undeconiposable aggregates, serving 

 as the primary basis of all tangible substances. 



It must be expected, however, that these elements will possess all 

 degrees of capacity for manifesting their presence, and that while some 

 will stand out boldly, cohere in vast masses, like iron, for example, 

 and in various ways render themselves obvious and obtrusive, others 

 will be ever hugging the confines of the imperceptible, and, like ozone, 

 will perpetually evade the full scrutiny of science. To this latter 

 class also belongs the substance which emits the green ray of the solar 

 spectrum, which has already led eminent chemists to conjecture that 

 it may be of simpler constitution than any recognized element, if not 

 the primary form of matter. 



Setting out with the elements, regarded as aggregates of a com- 

 paratively high order and stable organization, but differing from one 

 another in form, size, and molecular activities, as widely as the masses 

 they form differ in properties, the problem of the formation of the 

 higher orders of aggregates becomes comparatively simple. We find 

 ourselves already in the domain of experimental science where the 

 more or less completely demonstrated laws of chemistry and molecu- 

 lar physics lead us up to the formation of the various inorganic and 

 organic forms of matter. The constitution of the various substances 

 found upon the earth is readily determined by decomposing them and 

 weighing their constituents. The precise conditions, however, which 

 have resulted in their formation as we find them and brought about 

 the existing state of things in the universe, are not so easily determined, 

 and for this purpose a further extension of the general law of material 

 aggregation is required. 



The study of the earth's crust clearly indicates that very different 

 conditions have existed upon it in the remote past from those which we 

 now find. The facts as a whole prove beyond a doubt that our globe 

 has once been in a state both of greater or less liquidity and also of 

 great heat, and that, as its surface has cooled down, the solid parts, 

 to which alone we have access, have been formed, though to what 

 depth these extend we are still ignorant. But, notwithstanding certain 

 doubts which have from time to time been cast upon it, the theory 

 which was very early advanced as most in harmony with the probable 

 history of the planet, and according to which the cooling process has 

 not yet reached the great interior, which is therefore still in a heated 

 and molten, condition, still furnishes, perhaps, the most rational expla- 

 nation yet made of the phenomena which the earth presents, and also 

 best satisfies the a priori requirements. 



It is now generally believed that the present condition of our earth, 

 and also that of the entire solar system, has been the result of a cos- 

 mical process of development by which its matter, unchanged in quan- 

 tity, has been slowly condensed from a diffused nebulous state, occu- 

 pying enormously increased space a condition analogous to, if not 



