Let us go a step further, and suppose that the progress of discovery has made known certain facts lying behind the phenomena in question, to which they may all be referred. Let us suppose, that all bodies which gravitate towards each other are found to be embosomed in a subtile, ambient fluid, which connects them, as it were, into one system; that the positive and negative states of electricity are resolvable into the presence of two fluids standing in certain relations to each other; and that substances show chemical affinity for each other only when they are in opposite electrical conditions. Still, we have only advanced a step in the generalization, and the real, efficient _cause_ of the appearances is still hidden from us by an impenetrable veil. Gravitation is now referred to the communication of motion by impulse; electricity, to the combination and separation of different fluids; affinity, to the attraction or repulsion of these fluids. The latter classes of phenomena are more general, but not a whit more explicable, than the former. We have now fewer causes to seek for, but not one of these few has been discovered. When we have resolved electricity or gravitation into the presence of an elastic medium, it is a mere figure of speech to say, that we have discovered the _cause_ of the electric phenomena or of gravity. That is just as far off as ever; for we have yet to discover the principle whence flow _necessarily_ all the phenomena observable in fluids. It is the sole end and the highest ambition of science to discover as many as possible of the relationships which bind facts together, and thus to carry the generalization to the farthest point. Its office is not to discover causes, but to generalize effects. The investigation of real causes is quite given up, as a hopeless undertaking.