Now this duality which was thus assumed to exist in the nature of Galilean motion or velocity, making it relative for mechanical phenomena and absolute for electrodynamic ones, was perfectly acceptable, provided it was permissible to draw a sharp distinction between mechanics and electrodynamics, between space and the ether. But the entire trend of recent research had been to show that this distinction was unjustified. In the first place, matter seemed to be constituted by electrons and protons, hence to be reducible to phenomena of an electromagnetic nature. Then again, electromagnetic phenomena were known to develop mechanical forces. Where, then, was the essential difference between mechanical and electromagnetic phenomena? Under the circumstances how could we account for this anticipated duality in the palpable effects caused by a velocity through the ether, relative or physically meaningless for mechanical experiments, and capable of producing physical effects in electromagnetic ones? It appeared as though mechanical and electromagnetic phenomena should be susceptible of being placed on the same footing. We should then have to assume that mechanical phenomena together with electromagnetic ones would be affected by velocity through the ether, hence through space, or else to recognise that both electrodynamic and mechanical phenomena could never be influenced by this type of motion. If we should accept the first hypothesis, the Newtonian or mechanical principle of relativity would be overthrown, and with it the entire structure of Newtonian mechanics; and if we should accept the second hypothesis, our understanding of electromagnetic processes and of the ether would have to be modified profoundly. In either case, whether or not electromagnetic and optical experiments succeeded in detecting absolute Galilean motion, science seemed to be faced with a difficult situation.