The chair is designed to support a human body in a sitting posture, to be more exact, it is “a device for supporting the body of a man when his back and shins are positioned vertically, while his hips are positioned horizontally.” The layout of the chair looks like this: a sitting surface resting on a support (compulsory), a back, arm rests and others (optional). Then there is a wide scope for creation. 
 

 

A lot of chairs of different models have been created so far. The simplest one is a stool, more comfortable are chairs with a back and arm rests, as well as armchairs. Hard and soft, flexible, folding, rotating, wheeled, transformable… We can also recollect specialized seats – dental chair, car seat, or electric chair.
 

What did this variety begin with? The first chair was ground. An ideal piece of furniture! You don't need to wear it with you, but it is always at hand. You can sit where you want. It is not always comfortable though – at one moment it is wet, at another gnats and flies beset you. And the posture may be not quite convenient, sometimes it was even dangerous because an ancient man had to be very mobile (try to stand up rapidly when you are sitting on the floor)! First, you must have a seat that is neither wet nor cold, and second, it must be of a suitable height.

The first problem could be solved by putting a hide or a mat on the ground. And the log – the prototype of a stool, could solve both problems. A log – a fallen tree – is a horizontal cylinder. The point of contact of a man with the log surface is very small, because both surfaces are convexo-spherical. As a result the following problem may arise: 
 

It is better to sit on something flat. Suppose we cut a piece from a log and overturn it. It is convenient to sit on such a stub. It is stable, the height of the seat can be chosen at one's desire (though only once). But the useful property of a lying log – rollability – is lost. As for the vertical version of the log, some problems arise – it is a trifle too heavy and inconvenient to lift, many motions are to be made – overturning, rolling, overturning again. To make this piece of furniture less heavy, unnecessary material was beginning to be vertically removed. Only the seat itself (for the sake of convenience) and the base (for the sake of stability) had to remain wide, all the rest served for holding the seat at a necessary height. The shape of the upper part turned out to be comfortable for gripping. (You may remove more material. Admirable decorative effect is produced). Less and less of the material remains under the seat until only legs-supports remain.  

 

But lightness and carrying convenience are secondary properties. And how was the main function performed? A perfectly flat surface does not match the bends and convexities of a human body. It is necessary to match the surface of a stool seat with that of a human seat.

One of the methods is to change curvature, to go out to space. The stool surface may be bent in one direction – it may be given the form of the internal surface of a cylinder. Or it may be bent in two directions – the shape will correspond to the internal surface of a sphere. 

Such a surface has one small disadvantage – it is not individual. The surface curvature is rigidly preset. What is comfortable for one seat means callosity for another one. How can we make a stool that would be convenient for any user? 
 

Why not to place a varying object between a hard surface and a human body? A so-called “intermediary” between a stool seat and a man. This can be a pillow – any elastic material with deformable filler. It changes its shape exactly in accordance with the user's body. Then the 'intermediary' was attached to the seat so that it was always in its place. Thus a prototype of a soft chair was produced.  

 

There is another admirable method of matching the shape of a stool seat with that of a human body. This is a mat (or later a fabric). If its edges are fixed at a height and the middle part is left loose, then the weight of a sitting man deforms it to give it a necessary form. The X-shape of the base was stable. But somebody guessed to make the mounting movable and a folding chair was obtained. 
 

At that stage the compliance of the object with the function it performs became practically ideal. After that the chair has nowhere to evolve. Materials and manufacturing technologies change, additional, secondary functions, properties and purposes appear. Changed are the form and the image, but all of them are grandchildren and great-grandchildren of the log.
 

The stool allows unloading legs, but the load on the back remains. Why not to create a support for it? First attempts, modest and unassured, were made in ancient Egypt. A small vertical protrusion, only 10 cm high, appeared at the back surface of the seat.

It grows to support not only the sacrum, but also the upper part of the backbone and shoulders.The stool turned into a chair – a support not only for the pelvis, but also for the back. This means that the function predetermined the form of the seat and the load on the legs is reduced by the horizontal surface, while the vertical surface allows the back to relax.

 

Since the social stratification occurred, there have existed two basic types of chairs – domestic and representative, or the throne, for privileged members of society. Such a seat was usually made especially beautiful. But the main thing was that a man sitting on that chair had to have a lofty appearance. That is why such chairs had a straight back in order to ensure a proud bearing. Those chairs were also high, so that a man sitting on it could look taller than others. The inconvenience connected with the throne height was compensated by a footrest. The proud bearing does not imply that arms are lying modestly on the knees. One may proudly cross them on his breast, but that posture is inconvenient. If there are supports for a pelvis and a back, why not to add supports for arms, more exactly, for forearms?  

 

Further evolution of the chair, improving its controllability, matching it with special (for instance, professional) working conditions, providing it with new functions, using new materials and technologies remain beyond the scope of our short survey for the time being. But we would like to mention one chair version that is ideally matched with the user's body shape. We mean “Sacco” – a chair-sack invented by the Italian designers Gatti, Paolini and Teodoro. The leather covering is loosely filled with plastic granules. The filler easily takes the form that is convenient for a person sitting on the chair and then readily changes it to suit a next user. The user HIMSELF, by the weight and form of his body, controls the chair's parameters.