352 THE POPULAR SCIENCE MONTHLY. 



It may be said here, parenthetically, that all these recent attempts 

 (to one of which, by Prof. Challis, I had occasion to refer in my second 

 paper) to construe the apparent attractions of bodies as cases of ethereal 

 pressure and propulsion are simply returns to the state of scientific 

 anarchy which prevailed in celestial mechanics before Newton's time. 

 Prof. Spiller is evidently unaware that his theory — according to which, 

 force is an " incorporeal matter " — is nothing but a reproduction of Kep- 

 ler's speculations (not to speak of the Cartesian and Leibnitian theories 

 to which I have already alluded), in which the vortices supposed to 

 carry the planets along with them were asserted to be an " immaterial 

 species," capable of overcoming the inertia of bodies. It is plain that 

 this " immaterial species " is the same wooden iron which Spiller ex- 

 hibits under the name of " incorporeal matter," the only difference being 

 that the absurdity of Kepler's chimera was less glaring in the hazy 

 dawn of the mechanical notions of his time, than the extravagance of 

 Spiller's conceit in the light of the scientific atmosphere of our day. 



It is almost superfluous to say to the intelligent reader of these 

 papers that Spiller's " dead matter " is a nonentity, inasmuch as we 

 know nothing of material reality except through its action. And it is 

 hardly worth while to point out in detail that the hypothesis of dead 

 atoms is not only inadmissible, but wholly useless. Unchangeable 

 particles destitute of gravity and all other force, even if the action of 

 force upon them were conceivable, must be equally acted upon from 

 all sides by the omnipresent ether, and could, therefore, in no wise 

 help to establish differences of density, or other differences not con- 

 tained in or evolvable from the ether itself. They could not even 

 add to the extension of a body, much less to its hardness, being wholly 

 without the power of resistance ; but, waiving this, and granting for a 

 moment that extension without resistance is possible, they would sim- 

 ply be bubbles of void space encysted in the universal ether, and to 

 the differentiation of this ether alone all the phenomena of the material 

 world would be due. 



The truth is, that absolutely passive, dead matter is as unknown in 

 experience as it is inconceivable in thought. Every particle of mat- 

 ter of which we have any knowledge attracts every other particle in 

 conformity to the law of gravitation ; and every material element 

 exerts chemical, electrical, magnetic, thermic, and similar forces upon 

 other elements which in respect to these forces are its correlates. The 

 whole presence of matter to the senses consists in the manifestation 

 of power, in the exhibition of force. All this has been very clearly 

 seen and very explicitly stated by numerous physicists ; ■ but, unfor- 

 tunately, by most of them it has been speedily lost sight of in their 

 ulterior speculations. 



In what sense, then, can inertia be truly predicated of matter? 



1 Among those whose comprehension of this is clear, is M. Comte ; his observations 

 upon the subject (" Philosophie Positive," tome i., p. 375, et seq.) merits attentive perusal 



