Before strain gage-based load cells became the method of choice for industrial weighing applications, mechanical lever scales were widely used. Around 7000BC equal armed balance scale used by Sumerians for weighing precious metals and gems. The balance consists of a beam oscillating around a fulcrum and carrying a pan at each end. Weighing involves comparing standard weights of known mass with an object of unknown mass There are records from around 3000 BC showing that balance scales were used by Egyptians for general trade purposes.
Around 55BC the Romans brought steelyard scales to Britain. A steelyard differs from the balance, which has equal arms, because it has a beam with unequal arms. The steelyard is suspended from a hook, whose position represents the fulcrum. The shorter arm is fitted with a hook to hold the object being weighed. A counterweight, called a counterpoise, can be shifted along the length of the longer arm. The counterweight is moved until the longer arm reaches horizontal equilibrium. We read the weight from the position of the counterpoise on the scale. Graduated scales were marked on two or three sides of the beam giving the steelyard two or three capacity ranges.
In 1830 Thaddeus Fairbanks build the first platform scale by digging a pit for the lever arms of the scale, placing the platform level with the ground. This modification ended the task of having to hoist the entire load.
In 1843, English physicist Sir Charles Wheatstone devised a bridge circuit that could measure electrical resistances. The Wheatstone bridge circuit is ideal for measuring the resistance changes that occur in strain gages. The first bonded resistance wire strain gage was developed in the 1940s, roughly 97 years after Sir Wheatstone invented his circuit, when modern electronics caught up that the new technology feasible.
In 1973, the first fully electronic precision balance was introduced by Mettler Instrumente AG.
Today, except for certain laboratories where precision mechanical balances are still used, strain gage load cells dominate the weighing industry. Even in environments where a mechanical scale might do as well, a load cell is often used because of its compatibility with digital, computer-based instrumentation.
The earliest forms of our common chairs came into use from the sixteenth century. Chairs were only affordable by the royal people and were rarely made for the common man. Many styles and designs have come up since those ages when only the royal and high-class people could afford to have a chair. It is here that you will learn more about the chairs journey.
Chairs Before about 1500 chairs were a rarity, few homes had even one, and most people sat on benches, stools or chests. The chair, when one was to be found, was reserved for the use of royalty and the most noble. By the time of Henry VIII and Elizabeth I, armchairs of various types had begun to be made in quantity, and quite a number survive now. They are made of oak, with a straight or nearly straight back, with turned legs and curved arms, ornamented with carving or inlay. They have plain wood seats, and were used with the aid of a cushion.
Single chairs (those without arms) were probably made at an earlier date, but being less strongly constructed; few have survived that were made before about 1600. Most are quite plain, with the upper part of the back and the seat covered in silk or embroidery. As the seventeenth century progressed, and walnut or painted beech wood replaced oak, a number of fresh styles came and went. Turning, either in the form of bobbins or barley-twist was popular, and the use of caning instead of upholstery was introduced from the Far East. Finally, came the fashion of tall-backed chairs, heavily ornamented with turning and carving, with seat and back caned. Many of these were imported from France and Holland, where a similar fashion reigned, and it is a matter of argument as to where many of these chairs actually originated.
Gradually, caning lost favor and its place was taken by elaborate upholstery in velvet or figured silk, but in either case with deep-fringed and colored edgings. Although many of the single chairs were upholstered on both seat and back, others still with the high back featured a tall carved and pierced back panel and the first use of cabriole legs. By 1715 the cabriole leg was in general use, and the back of the chair had started to become square in shape: no longer was it the characteristic tall and narrow feature of the previous century. The centre of the back, called the 'splat' was usually a panel of solid or veneered wood and of shaped outline, and the top of the back was rounded. Most chairs showed some carving, especially in the form of the claw and ball foot. Some very finely carved chairs have feet in the shape of lions' paws, with lions' heads on the knees; others have arms, which finish in heads of eagles.
By 1740, with the coming of mahogany, the use of carving on chairs was widespread, the back continued to get lower until it was more or less square, and the cabriole leg remained popular. The top of the back was usually of a Cupid bow shape, the seat nearly square and often of generous size. Probably the most famous English chairs are those for which Chippendale shows designs in his book. The Director, where they are called 'ribband back chairs'. These have the back carved and pierced in an intricate pattern of ribbons with a central bow. A number of these masterpieces have survived the wear and tear of two hundred years.
The most common woods that were used for making chairs were the walnuts, mahogany, oak, and others. The legs of the chairs were designed differently and they were continuously upgraded with new styles and designs.
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