TWAS Twain who famously remarked that "everybody talks about the weather, but nobody does anything about it." In one sense, however, this is not entirely true. Securely encapsulated in our houses, offices or factories, we have achieved a fair measure of control over the "weather" we may experience in those environments.
The first step in this direction was the discovery of fire. It allowed man to supplement such heat as he required from clothing with further warmth from an external source. The technique was perfected by the ancient Romans who devised the hypocaust, a somewhat elaborate heating system in which air warmed outside a building was brought under the roof of each room, or behind the walls, through hollowed tiles. Such techniques were forgotten, however, with the decline of the Roman Empire, until resurrected relatively recently in the form of modern central heating.
But it is perhaps in the industrial world that the indoor climate may be most important, when specific conditions are required to suit the needs of individual products. In the case of cotton, wool, silk or even synthetic fibres, for example, the effective working of the material, and the quality of the end result, depend largely on operating at the right temperature and humidity. If the air is very dry at the time of spinning, the fibres fly apart under the electrical charge they soon acquire, and the yarn produced is fuzzy, or "oozy" as they call it, and incapable of being woven into high grade cloth. Very dry fibres, furthermore, tend to be brittle, and very damp ones slippery.
Another sensitive process is that of fine printing or lithography, where constant temperature and humidity are required if the paper is not to swell or shrink. If two or more printings in different colours are needed, successive impressions will not fit, or "register", if the dimensions of the paper have altered in the meantime the colours will overlap in places, and adjacent colours fail to join at others. And the electronics industry, too, is sensitive to temperature and humidity, and perhaps to an even greater extent, to dust; measurements on integrated circuits are of the order of one millionth of a millimetre, and microscopic particles of dust are just the right size to sabotage the Lilliputian circuitry.
For processes like these, it is essential that indoor conditions be quite independent of those, that nature may provide outside. This is achieved by sealing the environment, and arranging for the admission and escape of air, duly filtered and at a constant temperature and humidity to suit the work in hand.