It is now not merely in the larger and more obvious operations of Nature that we can trace this marvellous ubiquity of law, but in her most hidden processes and inmost constitution. At every point, we are forced to ask why things should be as they actually are, and how they came to be subject to conditions which they cannot be supposed to have created for themselves. Why, for example, should the ultimate elements of matter,--be they atoms, or electrons, or whatever else,--always and everywhere observe the same rules of the great game in which they serve as counters? Why, to take a concrete instance, should atoms of Hydrogen in Sirius, or in a star of the Milky Way, obey just the same laws as do those with which we make coal-gas or spirit of salt? These various atoms, as Lord Grimthorpe reminds us, have never been within billions of miles of one another. What is the mysterious influence which links them together across the depths of space? That they are so linked is obvious; for if we can ascertain the existence of such a substance in other spheres, it is only because the light it emits, exactly agrees when analyzed in the spectroscope with that of hydrogen flames in our own laboratories. How comes it, again, that the seventy different kinds of atoms, (to speak in round numbers)--are distributed--according to Mendeléeff's periodic law,--among some seven groups or families, the members of each group resembling one another in various particulars, wherein they differ from the rest? Or, to pass from atoms to molecules, (in which atoms of the same or of different kinds combine, to build up simple or compound substances respectively,)--how is it that molecules of the same kind are always constructed upon exactly the same model, resembling one another far more closely than sovereigns struck from the same die, or different copies of this morning's _Times_? It was in this uniformity of type, character and behaviour, repeated always and everywhere, in instances multiplied "beyond the power of imagination to conceive," that Sir John Herschel[125] saw a feature stamping atoms and molecules as "manufactured articles, and subordinate agents," which, no less than a line of spinning-jennies, or a regiment of soldiers clad in the same uniform, and going through the same evolutions, imply a controlling force directing things according to a definite system. These and innumerable other particulars of detail has Science added to the problem: but of anything which can supply an answer, she knows no more than did the first man who ever mooted the question within his own soul.