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From 8000 BC
From 3000 BC
6th century BC
Middle Ages
15th - 16th century
17th century
     Pendulum clock
     Pocket watch
     Pressure cooker
     Piano and forte

18th century
19th century
20th century
To be completed

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Barometer and atmospheric pressure: 1643-1646

Like many significant discoveries, the principle of the barometer is observed by accident. Evangelista Torricelli, assistant to Galileo at the end of his life, is interested in why it is more difficult to pump water from a well in which the water lies far below ground level. He suspects that the reason may be the weight of the extra column of air above the water, and he devises a way of testing this theory.

He fills a glass tube with mercury. Submerging it in a bath of mercury, and raising the sealed end to a vertical position, he finds that the mercury slips a little way down the tube. He reasons that the weight of air on the mercury in the bath is supporting the weight of the column of mercury in the tube.


If this is true, then the space in the glass tube above the mercury column must be a vacuum. This plunges him into instant controversy with traditionalists, wedded to the ancient theory - going as far back as Aristotle - that 'nature abhors a vacuum'. But it also encourages von Guericke, in the next decade, to develop the vacuum pump.

The concept of variable atmospheric pressure occurs to Torricelli when he notices, in 1643, that the height of his column of mercury sometimes varies slightly from its normal level, which is 760 mm above the mercury level in the bath. Observation suggests that these variations relate closely to changes in the weather. The barometer is born.


With the concept thus established that air has weight, Torricelli is able to predict that there must be less atmospheric pressure at higher altitudes. It is not hard to imagine an experiment which would test this, but the fame for proving the point in 1646 attaches to Blaise Pascal - though it is not even he who carries out the research.

Having a weak constitution, Pascal persuades his more robust brother-in-law to carry a barometer to different levels of the 4000-foot Puy de Dôme, near Clermont, and to take readings. The brother-in-law descends from the mountain with the welcome news that the readings were indeed different. Atmospheric pressure varies with altitude.


The pendulum clock: 1656-1657

Christiaan Huygens spends Christmas day, in the Hague in 1656, constructing a model of a clock on a new principle. The principle itself has been observed by Galileo, traditionally as a result of watching a lamp swing to and fro in the cathedral when he is a student in Pisa. Galileo later proves experimentally that a swinging suspended object takes the same time to complete each swing regardless of how far it travels.

This consistency prompts Galileo to suggest that a pendulum might be useful in clocks. But no one has been able to apply that insight, until Huygens finds that his model works.


A craftsman in the Hague makes the first full-scale clock on this principle for Huygens in 1657. But it is in England that the idea is taken up with the greatest enthusiasm.

By 1600 London clockmakers have already developed the characteristic shape which makes best use of the new mechanism - that of the longcase clock, more affectionately known as the grandfather clock.


The pocket watch: 1675

Nineteen years after making his model of the pendulum clock, Huygens invents a device of equal significance in the development of the watch. It is the spiral balance, also known as the hairspring (an invention also claimed, less convincingly, by Robert Hooke). This very fine spring, coiled flat, controls the speed of oscillation of the balance wheel. For the first time it is possible to make a watch which is reasonably accurate - and slim.

Both elements are important, for the sober gentlemen of the late 17th century are less inclined than their ancestors to wear jewels round the neck. A watch which will keep the time and slip into a waistcoat pocket is what they require.


Thomas Tompion, the greatest of English clock and watchmakers, is one of the first to apply the hairspring successfully in pocket watches (of which his workshop produces more than 6000 in his lifetime). The new accuracy of these instruments prompts an addition to the face of a watch - that of the minute hand.

The familiar watch face, with two concentric hands moving round a single dial, is at first considered confusing. There are experiments with several other arrangements of the hour and minute hand, before the design which has since been taken for granted is widely accepted.


Cartridges: 17th - 19th century

The efficiency of the flintlock mechanism is accompanied by a similar improvement in the loading of a musket. In the early years of hand-guns the soldier carries a powder flask, from which he tips a small charge of gunpowder into the pan of the gun and then a larger quantity down the barrel - following it with a round metal ball and sufficient wadding to hold it in place, before ramming the whole charge tight with his ramrod.

During the 17th century time is saved by providing the soldier with the correct charge, together with the ball, wrapped in a paper tube - the whole package being called a cartridge.


On the battlefield the soldier bites off the end of the paper tube, tips a small amount of powder into the pan of his flintlock and then pours the rest down the barrel, following it with the remains of the cartridge (the ball and the paper) which he rams tightly home.

This remains the standard procedure on the battlefield as long as muzzle-loading muskets are in use. Only in the 19th-century does it finally become obsolete, supplanted by breech-loading guns and metal cartridges with internal percussion caps.


Pressure cooker and piston: 1685-1690

In about 1685 Denis Papin, a French scientist working in England, demonstrates his 'digester'. It is a device familiar three centuries later as the pressure cooker. Papin's version is a cast-iron cylinder, about 6 inches in diameter and 18 inches long - much like a short length of drainpipe. The top section, which can be removed, is provided with a tight seal.

Papin places meat, bones and water in his digester. The tube can contain atmospheric pressure up to the point at which tin melts (about 210° C). To everyone's delight and amazement, the food is cooked very much sooner than the onlookers expect.


The digester includes an important mechanical innovation. Anticipating the danger that his scalding concoction of meat, bones and water may explode over the assembled company, Papin takes a crucial precaution. He provides the first recorded safety valve.

In addition to the main seal at the end of the cylinder, there is a second smaller aperture with its own seal. This smaller seal is held in place by a lever with an adjustable weight exerting the pressure.


By 1690 Papin is professor of mathematics at the university of Marburg. Here he makes a working model of a steam engine which is the first to incorporate one crucial element - the piston, forced up in its cylinder by the energy of expanding steam and then sucked down again by the vacuum when the steam cools and condenses.

Papin's machine is extremely leisurely because he uses the same container as both boiler and cylinder. A small amount of water is boiled in the vessel, forcing up the piston; the heat is removed and the steam cools, condensing and eventually pulling down the piston. The pace is unbearably slow, but the principle has a great future.


Piano and forte: c.1698

A maker of keyboard instruments in Florence, Bartolomeo Cristofori, begins work in about 1698 on a harpsichord che fa il piano e il forte (which can do soft and loud). He achieves this by devising a mechanism which will strike the strings rather than pluck them. In doing so, he greatly extends the range of effects available to the performer on the traditional harpsichord.

Early accounts emphasize this 'piano e forte' element of the new instrument, and from them it derives the name of pianoforte - or, in a more recent abbreviation, simply piano. By the end of the 18th century the piano occupies the central place in both professional and amateur music which it has held ever since.


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