The Song of Birds is popularly explained by the author of a work, entitled, "The Music of Nature," in which he illustrates the vocal machinery of Birds as follows:--"It is difficult to account for so small a creature as a Bird making a tone as loud as some animal a thousand times its size; but a recent discovery shows that in birds the lungs have several openings communicating with corresponding air-bags or cells, which fill the whole cavity of the body from the neck downward, and into which the air passes and repasses in the progress of breathing. This is not all. The very bones are hollow, from which air-pipes are conveyed to the most solid parts of the body, even into the quills and feathers. The air being rarefied by the heat of their body, adds to their levity. By forcing the air out of their body, they can dart down from the greatest heights with astonishing velocity. No doubt the same machinery forms the basis of their vocal powers, and at once resolves the mystery into a natural ordering of parts." This is a very pretty story; but, unfortunately, it is not correct, as already shown. A correspondent of the "Athenæum," writing in 1866, says:--"He would be a bold man who should say that Birds have no delight in their own songs. I have been led to conclude from experiments which I have made, and from other observations, that certain animals, especially Birds, have not only an ear for fine sounds, but also a preference for the things they see out of respect to fine colours or other pleasing external features. It is chiefly among Birds, when we consider the case of animals, that a taste for ornament and for glittering objects, often very startling and human-like, is to be found. The habits of the Pheasant, Peacock, Turkey, Bird of Paradise, several Birds of the Pigeon and Crow kind, and certain Singing Birds, are evidence. The Australian Satin Bower-Bird is the most remarkable of that class which exhibit taste for beauty or for glittering objects out of themselves--that is, beauty not directly personal; collecting, in fact, little museums of shells, gaudy feathers, shining glass, or bits of coloured cloth or pottery. It will be found with many Birds that fine plumes, a mirror, and an admirer, are not altogether objects devoid of interest.