It is not to be wondered at that ozone should thus have attracted general attention and interest as the distinctive and specially active agent present in the pure air of the sea-coast and the mountain-top. People not infrequently, on arriving at the seaside, sniff up the odours of decomposing seaweed (containing a little iodine), and think they are smelling the “ozone.” It is doubtful whether enough ozone is ever present in the atmosphere under simple natural conditions to affect even a highly-sensitive nose. But it is easy to produce enough by passing air over a silent electrical discharge to fill a large room with its peculiar smell. Whether it really is of benefit to the human being who inhales a properly limited percentage of it seems not to have been clearly decided by experiment, although both in London and the United States of America there are enterprising medical men who are convinced of its value and are using it. It would certainly seem that if the peculiar benefit which is often derived from sea air or from mountain air is due to the presence of this extra oxygen in such air, then nothing can be simpler or more rational than to introduce the proper and useful percentage of ozone into the air of specially-arranged chambers in London and other large towns, so that we can visit or even inhabit them and breathe ozonised air at will without going on a journey for it. But it is a remarkable fact that, as with various natural so-called “mineral waters,” so with various “airs” which people find beneficial—no one has yet clearly and decisively shown, in the first place, whether they exert any chemical effect of a special kind on the people who seem to benefit by drinking the one or breathing the other; still less has any one shown what is the particular chemical ingredient of the air or of the water of any given resort which exerts the beneficial effect attributed to that air or that water.