essential to their flight. Yet there is a real impediment in the way of Man navigating the air—and that is the excessive weight of the only great mechanical moving powers hitherto placed at his disposal. When Science shall have discovered some moving power greatly lighter than any we yet know, in all probability the problem will be solved. But of one thing we may be sure that if Man is ever destined to navigate the air, it will be in machines formed in strict obedience to the mechanical laws which have been employed by the Creator for the same purpose in flying animals.*

* The men of science in France are ahead of the men of science in England upon this subject. There is a Society established in Paris which announces in its very title the true fundamental principle of flight, "Société d'Encouragement pour la Locomotion Aérienne au moyen d'Appareils PLUS LOURDS que l'Air." The false principle of Buoyancy is thus eliminated and banished from the question.

CHAPTER IV.

APPARENT EXCEPTIONS TO THE SUPREMACY OF

PURPOSE.

ET, as we look at Nature, the fact will force

YET,

itself upon us that there are structures in which we cannot recognise any use; that there are contrivances which often fail of their effect; and that there are others which appear to be separated from the conditions they were intended to meet, and under which alone their usefulness could arise. Such instances occur in many branches of inquiry; and although in the great mass of natural phenomena the supremacy of Purpose is evident enough, such cases do frequently come across our path as cases of exception-cases in which Law does not seem to be subservient to Will, but to be asserting a power and an endurance of its own.

The degree of importance which may be attached to such cases as a source of real difficulty, will vary

with the character of the individual mind, and its capacity of holding by the great lines of evidence which run through the whole Order of Nature. It is with these cases as with the local currents which sometimes obscure the rising and falling of the tides. When watched from hour to hour, the greater law is clearly discernible by well-marked effects; but when watched from minute to minute, that law is not distinct, and there are waves which seem like a rebellion of the sea against the force which is dragging it from the land. The Order of Nature is very complicated, and very partially understood. It is to be expected therefore that there should be a vast variety of subordinate facts, whose relation to each other and to the whole must be a matter of perplexity to us. It is so with the relation in which different known laws of Nature stand to each other; much more must it be so with the far deeper subject of the relation which these laws bear to the Will and the intentions of the Supreme. But as cases of intention frustrated, of structure without apparent purpose, of organs dissociated from function and from the opportunities of use, are sometimes sources of diffi

culty, it may be well to consider this subject a

little nearer.

There is one explanation which it cannot be doubted applies to many cases, and this is the simple explanation, that we often mistake the purpose of particular structures in Nature, and connect them with intentions which are not and never were the intentions really in view. The best naturalists are liable to such mistakes. A very curious illustration is afforded by an observation of Mr Darwin, in his "Origin of Species." He says that "if green Woodpeckers alone had existed, and we did not know that there were any black and pied kinds, I daresay we should have thought that the green colour was a beautiful adaptation to hide this treefrequenting bird from its enemies." Now, this introduces us to a very curious subject, and one as well adapted as any other to illustrate the relation in which Law stands to Purpose in the economy of Nature.

There can be no doubt that the principle of adapted colouring with the effect and for the purpose of concealment, prevails extensively in various branches of the Animal Kingdom. It arises pro

bably, like all other phenomena, by way of Natural Consequence out of some combination of forces which are the instruments employed. We have no knowledge what these forces are, but we can imagine them to be worked into a law of assimilation, founded on some such principle as that which photography has revealed. It is true that Man has not yet discovered any process by which the tints of Nature can be transferred, as the most delicate shades of light can be transferred, to surfaces artificially prepared to receive them. Such a process is, however, very probably within the reach even of human chemistry, and it is one which is certainly known in the laboratory of Nature. The Chameleon is the extreme case in which the effect of such a process is proverbially known. Many fish exhibit it in a remarkable degree,—changing colour rapidly in harmony with the colour of the water in which they swim, or of the bottom on which they lie. The law on which such changes depend is very obscure, but it appears to be a natural process, as constant as all other laws are; that is, constant whenever given conditions are brought together. It is possible that