But if the historian of men's lives be audacious, much more so is he who would write of the lives of other animals. In some cases we may be fairly certain that those animals possess the same five senses as ourselves; but some may possess more, and some fewer; and in any case we cannot be sure that the quality of the sense is at all the same. The mystery of their daily lives is more impenetrable even than that of our own; and yet we can only employ the same means to pierce into it that we can employ with each other--observation and imagination. Moreover, our powers of observation are necessarily limited, because we cannot (except with the help of cumbrous appliances, and then not for long) live up in the air or under water; while our powers of imagination, being confined within the bounds of our human experience, may easily lead us hopelessly astray. The biographers of animals, in fact, are apt to endow their heroes and heroines with human attributes, and to make them think as human beings. I am myself a sinner in this respect, and it is in consequence of this sin that I am asked to introduce to the public Mr. Williamson's far sounder and deeper biography of Tarka, the Otter. If I have any claim to take by the hand one whose excellent work enables him very well to walk by himself, it is rather because I am an historian of one phase of human nature and in that capacity have been driven to exercise observation and imagination. But, it may be objected, an historian's business lies with musty papers and printed books. In a great measure, to his misfortune, it does; but these are not his only documents. Old buildings, old roads, and old tracks are a few among many others; and these the biographer of the wild animal shares with him; for the otter, as Mr. Williamson shows, has his world-old haunts and tracks, and not the otter only. Who, for instance, would assign any age to a badger-earth or to a peregrine falcon's eyrie unless he knew it to be recent? And, to descend to more precise matters, a stag's shed horns of last year are a document, if not human, at any rate cervine, from which he who runs may sometimes read much. Mr. Williamson is always on the watch for such documents as these, and he knows how to interpret them.