i88 THE POPULAR SCIENCE MONTHLY. 



have a thickness of from six to eight miles. The bombardment 

 would produce no other sensation than we now experience when 

 a gentle breath of air fans our cheeks. 



The picture which I have here jjresented is by no means the 

 product of a mere fantastic flight of imagination, but a con- 

 clusion strictly warranted by mathematical facts, and necessary 

 for the interpretation of the physical phenomena of nature. 



But chemistry has to go yet one step further, in order to ex- 

 plain and render intelligible the phenomena of combination and 

 aflBnity. We are driven to the conclusion that molecules are not 

 the ultimate particles of matter, but are built up of still smaller 

 bodies, the atoms. Thus, for instance, in a molecule of water we 

 have two atoms of hydrogen united to one of oxygen, and all 

 chemical processes have their source in the fact that the atoms of 

 two or more molecules of different substances detach themselves 

 and reunite again in a different fashion. 



Now, in order to obtain a better idea of the manner in which 

 the atoms are grouped in a molecule, we must look upon the latter 

 as a duster, the various parts of which are combined by a well- 

 regulated movement into a harmonious system. "We may well 

 resort, for comparison, to a process within our observation, though 

 on a far grander scale, which is admirably adapted for illustra- 

 tion. Let us look to our planetary system. 



The planets, with the sun, represent a stable system, just as 

 the atoms of a molecule represent such a one. In the case of our 

 solar system, the mass of the planets, compared with that of the 

 central body, is, of course, very insignificant. A far closer resem- 

 blance to our molecules is therefore presented by those systems 

 of the stellar world in which two or more large bodies, of nearly 

 the same size, revolve around their common center of gravity. 



This parallel between atoms and planets, molecules and solar 

 systems, opens before us a new and startling perspective. It 

 affords us a glance into that unfathomable abyss which hides the 

 mysteries of time and space, and holds in its dark recesses the 

 very secrets of existence. 



Astronomical science has shown that our sun, with the ma- 

 jority of the fixed stars visible to us, constitutes a great star- 

 cluster, the diameter of which must be estimated by hundreds, if 

 not thousands, of billions of miles. Of such star-clusters there 

 exist a great many, which, in their turn again, form a still grander 

 system, to which we also belong, and the boundaries of which are 

 indicated by the outermost limits of the milky way. 



How many of such galaxies may be hidden in the vastnesses 

 beyond, in the bosom of infinite space, we will never know, for 

 the light can only reach us from limited distances. Whatever 

 may be beyond that very farthest nebula, the pale light of which 



