space as occupied, and all motion produced by transfer to bodies in contact, the origin of motion is indeed reduced to a concept derived from our sense-experiences, but this view has also its difficulties. To mention only one of these, it is impossible in this hypothesis to explain the different densities of bodies from different combinations of a homogeneous original matter.
The origin of these contradictions is readily detected. They have their root in our incapacity to conceive of any thing save what we have experienced by either our external or our internal sense. In our endeavor to analyze the physical world, we start out from the divisibility of matter, the parts being to our eyes something simpler and more primitive than the whole. When in thought we carry on this division of matter ad infinitum, we act in perfect accordance with our sense-perceptions, and we meet with no obstacle in the process. But we make no advance whatever toward an understanding of things, since we, in fact, carry over into the region of the minute and the invisible the concepts we obtained in the region of the gross and the visible. Thus it is that we acquire the notion of the physical atom. If now we arbitrarily stop the process of dividing at some point where we are supposed to have reached philosophical atoms, that are indivisible, perfectly hard, and furthermore per se inefficient, being merely the carriers of the central forces, we are expecting that a matter which we think of under the concept of matter as known to us should, without the aid of any new principle of explication, develop new primordial properties, to explain the nature of bodies. Thus we commit the error which is manifested in the previously-mentioned contradictions.
No one, that has bestowed any thought on this subject, can fail to acknowledge the transcendental nature of the obstacles that face us here. However we try to evade them, we ever meet them in one form or another. From whatever side we approach them, or under whatsoever cover, they are ever found invincible. The ancient Ionian physical philosophers were no more helpless than we in presence of this difficulty. The natural sciences, with all the progress they have made, have availed naught against it, nor will their future progress be of any greater effect. We shall never know any better than we now do (to use the words of Paul Erman), "was hier im Raume spukt," the spectre that haunts the world of matter. For even the mind imagined by Laplace, exalted as it would be high above our own, would in this matter be possessed of no keener insight than ourselves, and hence we despairingly recognize here one of the limitations of our understanding.
But if we turn aside from this primordial limit, and postulate matter and force as understood, then, as we have said, the physical world is intelligible ideally. From the original condition of a revolving nebular sphere, the Kantian hypothesis, as further developed by Helm-
