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 assume, that this medium could suffer a compression, without giving resistance to it.

That transparent bodies can move, without communicating their full velocity to the contained aether, was proven by 's famous interference experiment with streaming water. This experiment, that later was repeated by and  on a larger scale, could impossibly have had the observed success, when everything within the tube would possess a common velocity. By that, only the behavior of nontransparent substances and very extended bodies remains questionable.

It should be noted, moreover, that we can imagine the permeability of a body in two ways. First, this property might not be present in individual atoms, yet when the atoms were very small compared to the gaps between them, it might be present in matter of greater extension; but secondly, it may be assumed - and this hypothesis I will use in the following - that ponderable matter is absolutely permeable, namely that at the location of an atom, also the aether exists at the same time, which would be understandable if we were allowed to see the atoms as local modifications of the aether.

It is not my intention to enter into such speculations more closely, or to express assumptions about the nature of the aether. I only wish to keep myself as free as possible from preconceived opinions about that substance, and I won't, for example, attribute to it the properties of ordinary liquids and gases. If it is the case, that a representation of the phenomena would succeed best under the condition of absolute permeability, then one should admit of such an assumption for the time being, and leave it to the subsequent research, to give us a deeper understanding.