As we are very liable, in common with the letter-writing world, to fall behindhand in our correspondence; and a little more liable because in consequence of our editorial function we receive more epistles than our individual share, we have thought that we might clear our account by writing a quarterly catholic letter to all and several who have honored us, in verse or prose, with their confidence, and expressed a curiosity to know our opinion. We shall be compelled to dispose very rapidly of quite miscellaneous topics. And first, in regard to the writer who has given us his speculations on Rail-roads and Air-roads, our correspondent shall have his own way. To the railway, we must say,—like the courageous lord mayor at his first hunting, when told the hare was coming,—“Let it come, in Heaven’s name, I am not afraid on’t.” Very unlooked-for political and social effects of the iron road are fast appearing. It will require an expansion of the police of the old world. When a railroad train shoots through Europe every day from Brussels to Vienna, from Vienna to Constantinople, it cannot stop every twenty or thirty miles at a German custom-house, for examination of property and passports. But when our correspondent proceeds to flying-machines, we have no longer the smallest taper-light of credible information and experience left, and must speak on _a priori_ grounds. Shortly then, we think the population is not yet quite fit for them, and therefore there will be none. Our friend suggests so many inconveniences from piracy out of the high air to orchards and lone houses, and also to other high fliers; and the total inadequacy of the present system of defence, that we have not the heart to break the sleep of the good public by the repetition of these details. When children come into the library, we put the inkstand and the watch on the high shelf until they be a little older; and Nature has set the sun and moon in plain sight and use, but laid them on the high shelf where her roystering boys may not in some mad Saturday afternoon pull them down or burn their fingers. The sea and the iron road are safer toys for such ungrown people; we are not yet ripe to be birds.