When people visit a mineral spring they generally do so with the double object of drinking the water and of bathing in it; with the drinking of mineral water we have, in this volume, nothing to do, but merely with bathing, and the reader will have gathered from the previous chapters, that, when bathing only is concerned, the exact composition of the water is not a matter of very great importance; since all baths act in the same way, by stimulating the skin, and the water of the bath is probably _never absorbed_. It is important to insist upon this point, because we find in several bath-puffs the assertion that their effect is due to the absorption through the skin of the material dissolved in the water of the bath. Such an assertion is contrary to the teaching of our leading physiologists. At all sea-bathing places the climate is, in one respect, the amount of barometric pressure, similar. The advantage of mineral baths over sea-baths very greatly lies in the fact that we are not only able to choose our water but also to choose our climate, and to have either a mountain climate with low barometric pressure, or a sea-level climate with a high barometric pressure, or a climate where the barometric pressure is intermediate between these two extremes. We must, in order to bring the effects of mountain climates vividly before the mind of the reader, refer again to the comparison which we have made elsewhere between the burning of fuel in a furnace, and the combustion which is constantly going on in our bodies. Experiments made by Professors Tyndall and Frankland on the combustion of candles at different altitudes, seem to give the clue to the explanation of the effects of mountain air upon our bodies. These gentlemen burnt candles of equal weight, and under similar conditions at Chamouni, and also on the top of Mont Blanc, which is 12,000 feet higher. They found that the amount of candle consumed in equal periods of time was the same in both situations, but that on the top of the mountain the candle gave out considerably _less light_ than it did in the valley. The diminution of the light was attributed with justice to the _completeness_ of the combustion, for the light emitted by a flame is mainly due to the unconsumed particles of carbon in a state of incandescence. Mountain air, being much more rarified than the air of low-lying valleys, contains much less oxygen in proportion to volume, but its lesser density seems to enable the oxygen to assume, as it were, a greater activity. It has also been found that bodies lose heat less rapidly in rarified atmospheres, so that presumably there is less need for heat-production on the mountain than on the plain; so that in mountain climates the body is saved a certain proportion of the combustion necessary for the generation of heat.