ances would have to be provided to transport them from the place where the ship might land to the station entrance.
It must not be assumed from what has been said in the foregoing that the writer regards the solution of the problems here considered as of no special value, for his views are just the opposite of this. The object aimed at has been to show that the wonderful things that it is expected will be accomplished by the solution of these problems will never be realized with regard to some because they are not possible, and are not likely to be realized by the others on account of inherent defects that the solutions may bring to light. The coal-battery problem will, no doubt, be worked out, in some form or other, but who can tell whether the objectionable features of it will or will not offset all its advantages? The hot-air engine is a far more perfect converter of energy, in theory, than the steam engine, but its defects when reduced to a practical form are such that it is of no value except for small power, and this may also turn out to be the case with the coal battery. The utilization of the energy of tides, solar heat, etc., is as possible to-day as at any future time; the fact that they are not utilized is proof that they are not considered as desirable as other forms of energy. In the future the cost of the apparatus for harnessing them may be so reduced as to render them available to a much greater extent than at the present time, but that they will ever revolutionize the industrial affairs of the world and drive the steam engine out of use is hardly a remote possibility. Aerial navigation will, no doubt, be accomplished, but in the opinion of the writer it will never be used for commercial purposes, simply because it can not, even if developed to the highest state of perfection, compete with transit on the surface of the earth, either in speed or cost of transportation. It may be used in warfare, but more than likely it will be confined to pleasure purposes.
