It may be that human progress will go on and on to the end of time without a break; that in the course of centuries mankind will surpass us in civilization, knowledge and power, as much as we surpass the earliest and rudest men we have yet found traces of: maybe infinitely more. In such a case, what would not the scholars of, say the year 5000 A.D., or any other future age, be willing to give for a comprehensive picture of humanity as it exists to-day--for a reasonably complete library of our literature, science, and art? We may safely assume that nothing of the sort will be possible if matters are left to take their natural course. By that time every structure, every machine, every book, every work of art, now in use or stored away in our libraries and galleries of art, will have disappeared, a prey to time, the elements, or the more destructive violence of man. On the other hand, it may be that, through repeated disasters of one sort or another, mankind, three thousand years hence, will have lost all the knowledge men ever possessed, and be slowly struggling upward for the hundredth time from inherited barbarism. In such a case, what enormous benefits might not accrue to man from a fortunate opening up of the wealth of knowledge we possess! In any supposable case between these extremes of progress or degradation, a legacy of art and learning, such as we might easily set apart for remote posterity, would certainly be acceptable, perhaps extremely useful. Besides, it might be possible for us to set such a worthy example to those who shall come after us that, come what might, humanity would never be left absolutely void of the means of instruction, nor any worthy human achievement be absolutely lost or forgotten. The experience of these later years has demonstrated the value of such legacies even when unintentional, unselected, and wretchedly fragmentary. It has made clear also how a legacy deliberately made may be indefinitely preserved. Roughly outlined, the carrying out of such a truly philanthropic enterprise would involve nothing more difficult than-- _First_. The construction of a practically indestructible treasure chamber in some secure place; and _Second_. The preparation of a library well calculated to withstand the corroding tooth of time. Two kinds of structures would meet the first demand--massive pyramids of covered earth or of solid masonry, or chambers hewn from the heart of some granitic hill. In low latitudes, where glacial action is not to be feared, the pyramidal form might be preferable: in more northern regions the rock-cut chamber would probably be at once cheaper and more durable. In either case, an elevated site should be chosen as a safeguard against submergence.