clear, into the Thames, and employs a fleet of steamers to carry the sludge practically out to sea. In both cases nature is left to finish the work. It is an axiom in engineering, as it should be in every calling, not to fly in the face of the working of nature, but to assist nature and nature will assist you. So, as there are means provided by which the refuse of the world is turned to good account, we have only to make use of them and the mysterious operations of nature will do the work. The septic treatment of sewage therefore seems to offer to us more prospect of dealing with the drainage of towns which have not the advantage of being able to discharge it into the open sea. Much has been already achieved in this direction, but much remains to be added by experience. Nevertheless, I anticipate that within a very few years the treatment of sewage will be as certain and successful as that of any other process or manufacture. The utilisation of natural sources of power must always be of importance, and the question seems to be now occupying a good share of attention. Water-power from rivers is usually the first in such schemes, and, in conjunction with longdistance transmission of energy by electrical means, offers a good field; but the scope and results are more restricted than are usually believed. It is very seldom that river rapids or falls can be harnessed into work except at a very large cost, and even where in more favourable cases power can be got in hand cheaply the distance over which it must be conveyed rapidly absorbs the efficiency, and it is wonderful how soon the economy of water-power is overtaken and surpassed by steam-power with all its low efficiency. The harnessing of the tides is another scheme oftener talked about than practised. There is probably no power in nature at once so vast, so visible, and so difficult to utilise as that of the tides. There are exceptional cases where tidal power has been economically used, but as yet they are very few. It seems to me, however, that much more might be done in this direction, and that there are places where a very considerable amount of energy might be made available by a judicious arrangement of floating wheels, dynamos, and secondary batteries, all under automatic control. The harnessing of wave-power on the sea-coast has been less often proposed, and, with the exception of bell-buoys, still more seldom put in practice. It may be found, however, that there are by this means greater facilities for gathering up and storing energy than by the tides. There appear to be situations peculiarly adapted for such an installation, such as at some breakwaters which have been designed by flying a good deal in the face of nature. At these places I believe the wavepower might be so used that it would effectually keep down