222 THE POPULAR SCIENCE MONTHLY. 



and uncommon in terms of that which is ordinary and common. But 

 that which is most obvious to the senses is both the earliest and most 

 persistent presence in consciousness, and thus receives the stamp of 

 the greatest familiarity. Now, the most obtrusive form of matter is 

 the solid, and for this reason it is that form which is first cognized 

 by the infant intellect of mankind, and thus serves as the basis for the 

 subsequent recognition of other forms. Accordingly we find that, on 

 the early stages of human history, the solid alone was apprehended as 

 material. It was long before even atmospheric air, obtrusive as it was 

 in wind and storm, came to be known as a form of matter. To this 

 day words signifying wind or breath — animus, spiritus, geist, ghost, 

 etc. — are the terms denoting that which is the fundamental correlate 

 of matter, even in the languages of civilized nations. And it is very 

 questionable whether either the ancient philosophers or the mediaeval 

 alchemists distinctly apprehended anj r aeriform substance, other than 

 atmospheric air, as material. It is certain that up to the time of Yan 

 Helmont, in the latter part of the sixteenth and the first decades of 

 the seventeenth century, agriform matter was not the subject of sus- 

 tained scientific investigation. 



It is obvious, then, that, while the progress of evolution in Nature 

 is from the aeriform to the solid state of matter, the progress of the 

 evolution of knowledge in the minds of men was conversely from the 

 solid to the aeriform ; and, as a consequence, the aeriform or gaseous 

 state came to be apprehended as a mere modification of solidity. For 

 the same reason, the first form of material action which was appre- 

 hended by the dawning intellect of man was the interaction between 

 solids — mechanical interaction — and from this, again, it followed that 

 the difference between the solid and the gas was apprehended as a 

 mere difference of distance between the solid particles, as produced by 

 mechanical motion. 



Again : familiarity, in the minds of ordinary men, is universally con- 

 founded with simplicity. And, the explanation of a phenomenon con- 

 sisting, as we have seen, in an exhibition of its genesis from its simplest 

 beginnings, the mind, in its attempts to explain the gaseous form, nat- 

 urally retraces the steps in the evolution of its ideas concerning matter 

 — of its concepts of matter — back to the earliest, most familiar, and 

 therefore apparently simplest form in which matter was and is appre- 

 hended, and assumes the solid particle, the atom, as the ultimate fact, 

 as the primary element for all representation and conception of ma- 

 terial existence. 



This is not the place to develop the important consequences which 

 flow from the total subversion of the prevailing concepts respecting 

 the constitution of matter that, in my judgment, is inevitable. When 

 it comes to be fully realized that an aeriform body is not a group of 

 absolute solids, but is elastic to the core; that a gas is a gas through- 

 out, and in its very essence ; that in the simplest states of matter there 



