Water and Air

In the preceding pages, water has been discussed as the representative of all that is liquid, but the fact has not yet been taken into account that water is always permeated with air or other gases, which are dissolved in it. This means that in all the processes that have hitherto been described, the gaseous state plays a certain, though minor, part, and that the laws of the element of air play into the element of water and vice versa (Plates 79 and 80). Wherever water flows, foaming and bubbling, or where it cascades and tumbles over stones, air is taken in and unites with it. The colder the water is, the more gases it can absorb, among which oxygen and carbon dioxide play an essential part.

Oxygen is of great importance for the natural purification of water and for all life within it. How important the intake of oxygen is, may be seen where this gas is absent in water, as a result of which the life in it is extinguished. This happens when water no longer moves sufficiently to allow it to be thoroughly permeated with air (stagnant water), or when the bed of the water is covered with so much rotting sludge, for instance through waste drainage, that the oxygen content of the water is no longer sufficient to break it down.

Cold water can absorb more oxygen than warm, which may have been the reason why in olden days fields were successfully irrigated in winter instead of in summer.

The respiration of water animals is adjusted entirely according to the air (i.e. oxygen) content of the water; they cannot live if there is too little oxygen dissolved in it. It is as though their gills were consolidations of the great inner surfaces of the streaming water itself; these surfaces we have seen to be related to processes of life. Here they serve to bring the oxygen in the water into the inner life processes of the creatures living in it.

The organic world of plants in lakes and seas is dependent on the content of carbon dioxide in the water. It is a process of cosmic proportions when in the changing seasons, with their growth and decline of vegetation, the carbon dioxide is inhaled and exhaled by the water of the oceans. If the carbon dioxide content of the air increases, the water immediately begins to absorb the surplus; if it decreases, the water releases it again, until a balance is achieved between the content of carbon dioxide in the water and that in the atmosphere. Thus when in autumn the plant world withers away and no longer inhales carbon dioxide, and when in the breaking down processes of plant substance, the disintegration of foliage, much carbon dioxide is released into the air, this is absorbed by the seas. When, however, in spring the plant world grows anew and forms the substance for its foliage out of the carbon dioxide in the air, the waters of the earth once again release some of the necessary carbon dioxide. Through this carbon dioxide cycle the whole building up and breaking down process of the plant world is integrated into the earth’s great system of respiration.

This property of water to form reservoirs of carbon dioxide is yet another of the ways in which it promotes life on the earth. We have seen how the seas are the great reservoirs of heat on this planet and how they regulate the climate; we now find that they are also the great regulators of the respiratory processes over the whole earth. Indeed, in its ability to absorb gases, water is mediator for the whole metabolism of the oceans on a grand scale. By absorbing carbon dioxide it increases its ability to dissolve solids. Water containing a large amount of carbon dioxide can, for instance, absorb more limestone than water containing only a little. Accompanying the play between the absorption out of the air and the release into the air of carbon dioxide, is a simultaneous ‘metabolism’ of the limestone content of the water.

This metabolism within the oceans is of great significance for the development of life in them. With its ability to absorb gases, water brings together the life on the solid continents with that in the deep seas; both regions depend on one another and form a unity. The life of each single creature can only be understood in relation to the life of the whole planet, in which—a small part of a great whole—it is embedded.

The laws of air and gas play their part in the inner life processes of organisms. Diffusion and osmosis are an expression of these laws; even quantitatively they are subject to them. But it is water that makes it possible for these processes to take place, thus rendering yet another service to life. This does not mean to say that the nature of the life processes is solely one of diffusion and osmosis; indeed, in many cases these are overcome by the processes of life.

As water on the one hand absorbs gases, so on the other it is prepared to relinquish its liquid form for a time and become vaporous. There is in the lower layers of the earth’s atmosphere no air that does not contain water. Indeed, the water contained in the air is the incentive for all meteorological events in the atmospheric mantle of the earth. Nearly all the different kinds of precipitation consist of water that has previously evaporated into the air. As it comes into contact with the air it dissolves into it until the saturation point of the air is reached. Every waterfall dissolves at its edges into an infinite number of the tiniest droplets, forming an inconceivable expanse of surface at which the two elements meet, and there the water surrenders itself to the air. The opposite process may be observed wherever water cascades and pours over stones into a pool. Air is then swept into the water, sparkling in white bubbles and creating great surfaces of contact at which the water can ‘breathe’ (Plates 2 and 4). So air takes part in the streaming movements of water, just as, in the play of clouds, water vapours join in the movements of the air (Plate 80).

Thus air and water mingle in an intermediate region; they move mainly according to the laws of liquid flow. Air complies to a great extent with these laws, only fully asserting its own nature under certain circumstances. We may therefore expect to find in air many of the forms of movement familiar to us in water, though often on a larger scale or at greater speeds.

In a stream, where water flows over stones, waves are formed, through which new water constantly flows. The same happens when air flows over a mountain range; behind the mountains the same kinds of waves arise, with new air constantly flowing through them. The waves are of course invisible in the transparent air, but sometimes in the high crests of the waves the water contained in the air separates out in the form of the clouds, thus making the crests visible as elongated, fish-shaped clouds, lying one behind the other. Between the separate clouds we may imagine the trough of the wave in which, because it lies lower, the water vapour does not become visible as a cloud (Plate 77). These waves sometimes remain in one place for hours on end, though new air is constantly streaming through them; they remain until the stream of air comes to rest or changes its direction. The wisp of cloud clinging to the peak of the Matterhorn is an example of a similar process; though it remains constant as a form, its substance changes moment by moment.

Spiralling and screw-like surfaces, too, appear in air as well as in water. We all know the spiralling formations made in the air by rising steam or smoke. Smoke and steam show how air goes through all the elements of movement that we have been examining in water. All the kinds of movement we have been studying, from the simple wave formation to the complicated formations of spiralling and in-curling surfaces, we find again here. What is so difficult to observe in water can be seen in the air over every cup of tea or burning cigarette.

Horizontal ‘tubes’ of air barrelling over the desert. Gliding birds make use of the ascending currents (after Idrac)

Idrac observed these movements in air on a large scale over the wide, hot spaces of the Sahara. Enormous cylinders of air with horizontal axes are made visible through the flight of desert birds. These birds glide in their thousands in long lines reaching from one horizon to the other. They hover on the ascending air currents between two adjacent cylinders or rollers of moving air.

Vertical cylinders of air may also be found towering over the land. Gliding birds make use of their upward stream and are often carried to great heights.

Vertically spiralling columns of air (thermals). Gliding birds are carried by them to great heights (after Idrac)

Vortices and trains of vortices arise in air, as in water, when it has to stream round obstacles. Wind forms vortices wherever it is obstructed by trees or branches, roofs or chimney-stacks. But because of the greater speed of air these will follow very much faster on one another than they would in the same process in water. In these high speeds, air begins to show something of its own nature, for now the rapidly forming sequence of vortices becomes audible. The gale howls around roofs and chimney-pots and whistles through the woods. Every pine needle and every tiny twig causes trains of vortices to arise; the vortices follow so closely on one another that the whistling, rushing sound arises. A wood of conifers breaks up the streaming air into an unbelievable number of tiny vortices. Here, too, there arise those vast extents of surface which in water we saw to be like sensitive ‘organs’. The moving forms are the same, but because of the greater speeds the air begins to differ from the element of water. What in air is audible, is silent in water. What is a sounding process in air, is slowed down in water and becomes visible as form.