Now if, as most philosophers of the present day seem to consider, there is no chemical union of the gases constituting the atmosphere, it may be supposed that, according to their respective weights, a partial separation and subsidence of the heavier will take place, while the lighter will chiefly compose the upper portion--thus, for example, a stratum of nitrogen will surmount a stratum of mixed nitrogen and oxygen, and this a stratum of mixed nitrogen, oxygen, and carbonic acid. The following passage from the Penny Magazine will illustrate this theory: "A law is found to prevail in the mixture of gases and vapours, as universal as is that relative to their expansion arising from temperature, namely, that two gases in a state of mixture exercise no influence one upon the other, except communication of temperature, but that each is disposed in exactly the same way as it would be if the other were not present. Thus it is found, entirely contrary to all previous notions, that no pressure of dry air upon water exerts the least influence in preventing the formation of steam, which goes on exactly as if the space above were a vacuum, and continues until further evaporation is stopped by the pressure of the steam already created. It is found that no pressure of one gas can confine another in water; but that, supposing a bottle partly full of water, the gas confined in the water will escape to the surface, and distribute itself in precisely the same way as if the other gas were not present. By this it is not meant that the action, commonly called mechanical, cannot take place, or that a stream of hydrogen would not trouble the air; but only that the permanent settlement of one gas is not affected in any way by the presence of another, so long as no chemical action is excited.