Vacuum applications: the Nernst lamp

Nernst lamps were an early form of electrically powered incandescent lamps. Nernst lamps did not use a glowing tungsten filament. Instead, they used a ceramic rod that was heated to incandescence. Because the rod (unlike tungsten wire) would not further oxidize when exposed to air, there was no need to enclose it within a vacuum or noble gas environment; the burners in Nernst lamps could operate exposed to the air and were only enclosed in glass to isolate the hot incandescent emitter from its environment.
Developed by Walther Nernst in 1897 at Goettingen University, these lamps were about twice as efficient as carbon filament lamps and they emitted a more "natural" light (more similar in spectrum to daylight). The lamps were quite successfully marketed for a time, although they eventually lost out to the more-efficient tungsten filament incandescent light bulb. One disadvantage of the Nernst design was that the ceramic rod was not electrically conductive at room temperature so the lamps needed a separate heater filament to heat the ceramic hot enough to begin conducting electricity on its own.
In the U.S., Nernst sold the patent to George Westinghouse who founded the Nernst Lamp Company at Pittsburgh in 1901.
After Nernst lamps fell into obsolescence the term "Nernst glower" went on to be used to describe the infrared-emitting source used in IR spectroscopy devices. (Recently, even this term has become obsolete as Nernst glowers have been largely replaced for this purpose by silicon carbide glow bars which are conductive even at room temperature and therefore need no preheating.).
Glower or Glowbar or even Globar, is indeed a term indicating a silicon carbide rod of 5 to 10 mm width and 20 to 50 mm length which is electrically heated up to 1000 to 1650 °C (1800 to 3000 °F). When combined with a downstream variable interference filter, it emits radiation from 4 to 15 micrometres wavelength

Vacuum applications: the Edison incandescent light bulb lamp

Thomas Edison filed his first patent application for "Improvement In Electric Lights" on October 14, 1878 (U.S. Patent 0,214,636). After many the experiments with platinum and other metal filaments, Edison returned to a carbon filament. The first successful test was on October 22, 1879, and lasted 13.5 hours. Edison continued to improve this design and by Nov 4, 1879, filed for a U.S. patent (granted as U.S. Patent 0,223,898 on Jan 27, 1880) for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires". Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways," it was not until several months after the patent was granted that Edison and his team discovered that a carbonized bamboo filament could last over 1200 hours.
The United States Patent Office gave a ruling October 8, 1883, that Edison's patents were based on the prior art of William Sawyer and were invalid. Litigation continued for a number of years. Eventually on October 6, 1889, a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. In the 1890s, the Austrian inventor Carl Auer von Welsbach worked on metal-filament mantles, first with platinum wiring, and then osmium, and produced an operative version in 1898. In 1898 he patented the osmium lamp and started marketing it in 1902, the first commercial metal filament. On December 13 1904, Croatians Aleksandar Just and Franjo Hanamanwere granted a Hungarian patent (No. 34541) for a tungsten filament lamp, which lasted longer and gave a brighter light than the carbon filament. Tungsten filament lamps were first marketed by the Hungarian company Tungsram in 1905, so this type is often called Tungsram-bulbs in many European countries.
In 1913 Irving Langmuir found that filling a lamp with inert gas instead of a vacuum resulted in twice the luminous efficacy and reduction of bulb blackening.
Nowadays incandescent light bulbs consist of a glass bulb with a filament of tungsten wire inside the bulb, through which an electric current is passed. The bulb is first evacuated and then filled with an inert gas such as argon to reduce evaporation of the filament.
An electrical current heats the filament to typically 2000 K to 3300 K, well below tungsten's melting point of 3695 K (6192°F). Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a continuous spectrum. The useful part of the emitted energy is visible light, but most energy is given off as heat in the near-infrared wavelengths.
In order to improve the efficiency of the lamp, the filament usually consists of coils of fine wire, also known as a "coiled coil". The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. Due to the coils creating gaps, such a filament has a lower surface area than the perceived surface area of the filament, and so evaporation is reduced. If the filament is then run hotter to bring back evaporation to the same rate, the resulting filament is a more efficient light source.

If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown tungsten nitride, brown tungsten dioxide, violet-blue tungsten pentoxide, and yellow tungsten trioxide which then deposits on the nearby surfaces or the bulb interior.
In a conventional lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope. When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, depositing preferentially on the uppermost part of the envelope and blackening just that portion of the envelope. A very small amount of water vapor inside a light bulb can significantly affect lamp darkening. Water vapor dissociates into hydrogen and oxygen at the hot filament. The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp. Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle.

Vacuum applications: the incandescent light bulb lamp ancestors

Over 20 different types of incandescent lamps were invented prior to the first commercially practical incandescent lamp created by Thomas Edison in 1879. A lamp, superior to the others because of a combination of three factors:
- an effective incandescent material,
- a higher vacuum than others were able to achieve
- the fact that Edison invented an entire, integrated system of electric lighting, where the lamp was a small component in an entire system of electric lighting.
Already in 1802, Humphry Davy created the first incandescent light by passing the current through a thin strip of platinum. It was not bright enough and in 1809, Davy also created the first arc lamp by making a small but blinding electrical connection between two carbon charcoal rods connected to a 2000-cell battery. Over the first three-quarters of the 19th century many experimenters worked with various combinations of platinum or iridium wires, carbon rods, and evacuated or semi-evacuated enclosures. Many of these devices were demonstrated and patented.
In 1840, British scientist Warren de la Rue enclosed a coiled platinum filament in a vacuum tube and passed an electric current through it. The design was based on the concept that the high melting point of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain fewer gas molecules to react with the platinum, improving its longevity. Although an efficient design, the cost of the platinum made it impractical for commercial use.
In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, with a design using platinum wires contained within a vacuum bulb. In 1845, American John W. Starr acquired a patent for his incandescent light bulb involving the use of carbon filaments. He died shortly after obtaining the patent. Aside from the information contained in the patent itself, little else is known about him. In 1851, Jean Eugène Robert-Houdin publicly demonstrated incandescent light bulbs on his estate in Blois, France. His light bulbs are on permanent display in the museum of the Chateau of Blois.
In 1872 A. N. Lodygin invented an incandescent light bulb. In 1874 he obtained a patent for his invention. For a filament, Lodygin used a very thin carbon rod, placed under a bell-glass. In August 1873 he demonstrated prototypes of his electric filament lamp in the physics lecture hall of the Saint Petersburg Institute of Technology. In 1873–1874 he conducted experiments with electric lighting on ships, city streets, etc. In 1874, the Petersburg Academy of Sciences awarded him with a Lomonosov Prize for his invention of the filament lamp. That same year, Lodygin established “Electric Lighting Company, A.N. Lodygin and Co”. In 1899, Petersburg Institute of Electrical Engineering awarded Lodygin with the honorary title of electrical engineer.
In a suit filed by rivals seeking to get around Edison's lightbulb patent, German-American inventor Heinrich Göbel claimed he developed the first light bulb in 1854: a carbonized bamboo filament, in a vacuum bottle to prevent oxidation, and that in the following five years he developed what many call the first practical light bulb. Lewis Latimer demonstrated that the bulbs which Göbel had purportedly built in the 1850s, had actually been built much later, and found the glassblower who had constructed the fraudulent exhibits. In a patent interference suit in 1893, the judge ruled Göbel's claim "extremely improbable".
In 1850 the English physicist and chemist Joseph Wilson Swan began working with carbonized paper filaments in an evacuated glass bulb. By 1860 he was able to demonstrate a working device but the lack of a good vacuum and an adequate supply of electricity resulted in a short lifetime for the bulb and an inefficient source of light. By the mid-1870s better pumps became available, and Swan returned to his experiments.
With the help of Charles Stearn, an expert on vacuum pumps, in 1878 Swan developed a method of processing that avoided the early bulb blackening. This received a British Patent No 8 in 1880. On 18 December 1878 a lamp using a slender carbon rod was shown at a meeting of the Newcastle Chemical Society, and Swan gave a working demonstration at their meeting on 17 January 1879. It was also shown to 700 who attended a meeting of the Literary and Philosophical Society of Newcastle on 3 February 1879. These lamps used a carbon rod from an arc lamp rather than a slender filament. Thus they had low resistance and required very large conductors to supply the necessary current, so they were not commercially practical, although they did furnish a demonstration of the possibilities of incandescent lighting with relatively high vacuum, a carbon conductor, and platinum lead-in wires. Besides requiring too much current for a central station electric system to be practical, they had a very short lifetime. Swan turned his attention to producing a better carbon filament and the means of attaching its ends. He devised a method of treating cotton to produce 'parchmentised thread' and obtained British Patent 4933 in 1880. From this year he began installing light bulbs in homes and landmarks in England. His house was the first in the world to be lit by a lightbulb and so the first house in the world to be lit by Hydro Electric power. In the early 1880's he had started his company.

10_At the end .. what is vacuum?

Vacuum is defined on encyclopaedia as “absence of matter”, “a space empty of matter”, “a space in which the pressure is significantly lower than atmospheric pressure”, “a state of emptiness”, “a void”, “a state of being insulated and sealed off from external or environmental influences”.
A less philosophical and more mathematical definition however refers Vacuum as “whatever volume where the pressure is lower than the atmospheric one”.

In a volume, particles are in constant motion. They hit the walls of the container and exert a force on its surface area, which is called "pressure". The force per unit area of the vessel is measurable and it is called pressure. Therefore, a pressure measurement will just give the number and intensity of particle impacts on a unit of surface area.

The highest pressures ever obtained in a laboratory is the respectable number of 1030 bar, a pressure larger than the one obtained before a supernova explosion. It was produced in a storage ring at CERN (Centre Européenne pour la Recherche Nucléaire) at Geneva, Switzerland during head-on collisions of two fast lead nuclei. Compared with this value, the maximum static pressure is of the order of 106 bar, reached in diamond Anvil cells.

On the other hand, the lowest pressure or, in other words the highest vacuum generated in laboratory, is of the order of 10-17 bar, which corresponds to just a few hundred particles in one cm3 and which was also obtained at CERN. One should compare this with a number of ~ 1019 particles per cm3 at atmospheric pressure and room temperature.

Therefore, between the highest and lowest pressure there are 47 orders of magnitude in between. But even the best vacuum obtained on earth is a high-pressure area compared with the almost total emptiness between stars in space. Accordingly, besides pressure vacuum is characterised by the density of particles. The interstellar particle density in the Milky Way, for instance, consisting of gas, plasma and dust, is only ~ 5 x 104 particles per m3. Between Galaxies one has only one particle or at most a few of them per m3. If one would distribute homogeneously the total matter of the universe in space, one would still have an extremely low particle density of only 3 particles per m3.

The enormous range of about 60 orders of magnitude between the maximum density calculated for a black hole and almost totally empty regions in space.

Nevertheless, even the almost perfect vacuum of interstellar space is not empty at all. There is electromagnetic radiation everywhere or superstrong fields, which are even able to generate new particles. Even if we would succeed to construct an empty volume, totally shielded against outside radiation, cooled to absolute zero temperature to reduce radiation from its walls, there would still be zero-point energy radiation emitted from the wall particles which are never totally at rest due to Heisenberg´s uncertainty principle.
Absolute vacuum is unstable: at the end “Vacuum is more full than the plenum”.

The first pump was invented in the beginning of XIII century

The first pump invented was a suction pump, created in 1206 by the Arabic engineer and inventor, Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī (1136 – 1206) a prominent Arab polymath: a scholar, inventor, mechanical engineer, craftsman, artist and astronomer from Al-Jazira, Mesopotamia who lived during the Islamic Golden Age. Known as the “Arabic Leonard de Vinci” he is also famous for having written the Book of Knowledge of Ingenious Mechanical Devices in 1206, where he described fifty mechanical devices along with instructions on how to construct them.



In 1206, Al-Jazari described the first suction pipes, suction pump, double-action pump, valve, and crank-connecting rod mechanism, when he invented a twin-cylinder reciprocating piston suction pump. This pump is driven by a water wheel, which drives, through a system of gears, an oscillating slot-rod to which the rods of two pistons are attached. The pistons work in horizontally opposed cylinders, each provided with valve-operated suction and delivery pipes. The delivery pipes are joined above the centre of the machine to form a single outlet into the irrigation system. This may be the only one of al-Jazari's water-raising machines which had a direct significance for the development of modern engineering. This pump is remarkable for three reasons:
• The first known use of a true suction pipe (which sucks fluids into a partial vacuum) in a pump.
• The first application of the double-acting principle.
• The conversion of rotary to reciprocating motion, via the crank-connecting rod mechanism.
Al-Jazari's suction piston pump could lift 13.6 metres of water, with the help of delivery pipes. This was more advanced than the suction pumps that appeared in 15th-century Europe, which lacked delivery pipes. It was not, however, any more efficient than a noria (a machine for lifting water into a small aqueduct, either for the purpose of irrigation or to feed seawater into a saltern) commonly used by the Muslim world at the time.
The suction pump later appeared in Europe from the 15th century. Taqi al-Din's six-cylinder 'Monobloc' pump, invented in 1551, could also create a partial vacuum, which was formed "as the lead weight moves upwards, it pulls the piston with it, creating vacuum which sucks the water through a non return clack valve into the piston cylinder."

If you want to see the mechanism of al –Jazari’s pump, go to
http://dmmf.mec.uniroma2.it/Sito%20Meccanismi/Filmati/Assieme_Pompa.m1v
http://dmmf.mec.uniroma2.it/Sito%20Meccanismi/Filmati/Particolare_Pompa.m1v

Pressure conversion units

In the International System of unit the units of measure of the pressure is Newton to the square meter (N/m2) defined Pascal (Pa). For convention the atmosphere is defined as the pressure to sea level from one high mercury column 760 millimeter (1 atm ~ 10e+5 Pa).

Pascal (Pa) is the metric SI unit of pressure and the standard pressure unit in the MKS metric system, equal to 1 Newton per square meter. In English terms, 1 Pascal is only 0.000145 pounds per square inch (0.020885434 lbf/ft2 or 0.00750 mmHg). Thus pressure is more commonly measured in kilopascals (kPa), with 1 kPa = 0.145 lbf/in2. For automatic pressure conversion:
http://www.coleparmer.com/Techinfo/converters/commpressure.asp

Pressure definition

where:
p is the pressure,
F is the normal force,
A is the area.


Pressure is an effect which occurs when a force is applied on a surface. The symbol of pressure is p (lower case).

Pressure is a scalar quantity, and has SI units of Pascals; 1 Pa = 1 N/m2, and has British units of psi; 1 psi = 1 lb/in2.
Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point.
The SI unit for pressure is the pascal (Pa), equal to one newton per square meter (N•m-2 or kg/m•s2). This special name for the unit was added in 1971; before that, pressure in SI was expressed simply as N/m2.
Non-SI measures such as pound per square inch (psi) and bar are used in parts of the world. The cgs unit of pressure is the barye (ba), equal to 1 dyn•cm-2. Pressure is sometimes expressed in grams-force/cm2, or as kg/cm2 and the like without properly identifying the force units. But using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as units of force is expressly forbidden in SI. The technical atmosphere (symbol: at) is 1 kgf/cm2. In US Customary units, it is 14.696 psi.
Some meteorologists prefer the hectopascal (hPa) for atmospheric air pressure, which is equivalent to the older unit millibar (mbar). Similar pressures are given in kilopascals (kPa) in most other fields, where the hecto prefix is rarely used. The unit inch of mercury (inHg, see below) is still used in the United States. Oceanographers usually measure underwater pressure in decibars (dbar) because an increase in pressure of 1 dbar is approximately equal to an increase in depth of 1 meter. Scuba divers often use a manometric rule of thumb: the pressure exerted by ten metres depth of water is approximately equal to one atmosphere.
The standard atmosphere (atm) is an established constant. It is approximately equal to typical air pressure at earth mean sea level and is defined as follows:
standard atmosphere = 101325 Pa = 101.325 kPa = 1013.25 hPa.

The weight of air

Using a piston in a cylinder, Otto von Guericke showed that when a vacuum was created on one side of the piston, the atmosphere would move the piston and a considerable mass through a distance, thus performing work. In 1672 he made a cylinder with a close fitting piston, all that strongly fixed in the vertical position.

By a rope and pulley 20 men effortlessly raised the piston to the top of the cylinder. Von Guericke had earlier prepared a large hollow sphere from which he had removed the air using a vacuum pump of his invention. When the sphere was connected to the cylinder atmospheric pressure pushed the piston down in spite of the efforts of the 20 men to restrain it. This demonstrated that the atmosphere was a potential source of energy but a vacuum was also needed to make use of it. No easy means existed of creating a vacuum except by a mechanical pump. This became the basic principle of the Newcomen steam engine (1712) i.e. the first practical device to harness the power of steam to produce mechanical work.

Otto von Guericke and the Magdeburg horses

Otto Gericke was born as son of a patrician family resident for three centuries in Magdeburg. Guericke family inherited extensive property both in the city and in the countryside around it. At the age of 15, he entered the Faculty of Arts at the Leipzig University. When Otto Gericke was 18 years old, his father died and in 1621 he went to Jena to study at the university there. To complete his studies, Otto Gericke studied in Leiden (Netherlands) in 1623. In 1626, at the age of 24, Otto Gericke returned to Magdeburg and married shortly thereafter. When Guericke returned home after his education, he was elected alderman of Magdeburg almost immediately, and he served the city continuously over the following fifty years. In 1630, he became city contractor. After the destruction of Magdeburg in 1631, as part of the Thirty Years War, he drew up a map of the city for the Swedish authorities. Since he had lost everything for the moment, Guericke became a military engineer in the army of Gustavus II Adolphus of Sweden, though the locale of the work was mostly Magdeburg, and then when control of the city passed into the hands of the Elector of Saxony in 1635, in his service. In this capacity, and also in his capacity as a magistrate of the city, Guericke played a large role in its reconstruction, both its fortifications and its bridges over the Elbe.
He especially looked into problems of constructing fortresses for which mathematics, mechanics and geometry were the most important subjects. After finishing his studies, he went on a nine months journey through France and England as young men of noble houses were entitled to.
Otto von Guericke proved at last that a vacuum could exist, against the common belief that vacuum was possible. Creating a vacuum was essential for all kinds of further research into electronics and other innovations. Besides being an inventor and a philosopher, Otto von Guericke served as the mayor or Burgermeister of Magdeburg, Germany from 1646 to 1676.
The hand bellows, used by early smelters and blacksmiths for working iron and metals, was a simple type of air compressor and the first pneumatic device. During the 17th century, Otto von Guericke experimented with and improved air compressors. In 1650, Otto von Guericke invented the air pump, used to create a partial vacuum.
In 1657, Guericke carried out his famous demonstration that several teams of horses could not pull apart two joined hemispheres when the air within had been evacuated. Then In 1663, Guericke demonstrated the power of a vacuum with his Magdeburg Hemispheres to Emperor Ferdinand III. During public demonstrations, teams of horses would attempt to pull the hemispheres apart which were held together by the force of atmospheric pressure created using his vacuum pump.
In 1663, Otto von Guericke finished his work "Experimenta nova Magdeburgia de vacuo spatio" ("New Magdeburg Experiments About the Vacuum"), published in Amsterdam 1672. Von Guericke dedicated his Experimenta nova to the Elector of Brandenburg. He received no money for the book because he was known to be wealthy. Guericke used his air pumps for many other experiments including experiments with electricity and magnetism. He proved that a lodestone, or magnet, can attract iron even in a vacuum; and that electrical attraction works in a vacuum as well. Air is needed by neither magnets nor electrics. It is especially significant that air is not needed for electrical attraction.

The barometer experiments made by Blaise Pascal

A mercury barometer has a glass tube of at least 33 inches in height, closed at one end, with an open mercury-filled reservoir at the base. The weight of the mercury actually creates a vacuum in the top of the tube. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir. Since higher temperature at the instrument will reduce the density of the mercury, the scale for reading the height of the mercury is adjusted to compensate for this effect.
Torricelli documented that the height of the mercury in a barometer changed slightly each day and concluded that this was due to the changing pressure in the atmosphere. He wrote: "We live submerged at the bottom of an ocean of elementary air, which is known by incontestable experiments to have weight".
The mercury barometer's design gives rise to the expression of atmospheric pressure in inches or millimeters (torr): the pressure is quoted as the level of the mercury's height in the vertical column. 1 atmosphere is equivalent to about 29.9 inches, or 760 millimeters, of mercury. The use of this unit is still popular in the United States, although it has been disused in favor of SI or metric units in other parts of the world. Barometers of this type normally measure atmospheric pressures between 28 and 31 inches of mercury.
Although Evangelista Torricelli is universally credited with inventing the barometer in 1643, two other noteworthy efforts must be cited. Historical documentation also suggests Gasparo Berti, an Italian mathematician and astronomer, built unintentionally water barometer sometime between 1640 and 1643. French scientist and philosopher Rene Descartes described the design of an experiment on atmospheric pressure determination as early as 1631, but there is no evidence that he built a working barometer at that time.

By 1646, Pascal had learned of Torricelli's experimentation with barometers. Having replicated an experiment which involved placing a tube filled with mercury upside down in a bowl of mercury, Pascal questioned what force kept some mercury in the tube and what filled the space above the mercury in the tube. At the time, most scientists contended that, rather than a vacuum, some invisible matter was present.

Mathematician, physicist, theologian and inventor of the first digital calculator, Pascal lived in the time when Copernicus' discovery. Blaise Pascal was sickly, precocious child, that grew up without the company of other children. Pascal’ mother died unfortunately at his early age. He studied privately, tutored mostly by his father, Etienne, who was a scientist and a government official. For a time his father was disgraced for complicity in a bond-holders' protest, but he was rehabilitated with the help of Richelieu's niece. When his father died, he was able to leave a sufficient patrimony to his son and his two daughters. It is normally said that intelligence is generally born from sufferance. We really hope this is not the only way. However , together with Pierre de Fermat, Pascal invented the calculus of probabilities and laid the foundations for Gottfried Wilhelm von Leibniz's infinitesimal calculus. In 1647 Pascal invented a calculating machine – becoming one of the fathers of the Computer Age – and later the barometer, the hydraulic press, and the syringe.
Experimenting with the vacuum, Pascal published in 1663 his study TRAITÉ DE LA PESANTEUR DE LA MASSE DE L'AIR, where he argued that "experiments are the true teachers which one must follow in physics. In Clermont Pascal demonstrated how the weight of the Earth's atmosphere balanced the mercury in the barometer.
Pascal’s experiments with the barometer proved the now familiar facts that atmospheric pressure (as shown by the height of the mercury in the barometer) decreases as altitude increases, and also changes as the weather changes. Indeed he had a barometer carried to the top of the Puy de Dôme, in the Massif Central in France, where the level of the mercury column fell to a few inches lower than at normal ground level. Pascal correctly interpreted this variation as a result of the lowering of air pressure at higher altitudes.
Having replicated an experiment which involved placing a tube filled with mercury upside down in a bowl of mercury, Pascal questioned what force kept some mercury in the tube and what filled the space above the mercury in the tube. At the time, most scientists contended that some invisible matter was present there—not a vacuum.

The “Argento vivo” Experiment by Evangelista Torricelli

Italian mathematician and physicist, born at Faenza, 15 October, 1608, Torricelli was educated at the Jesuit college of Faenza, where he showed such great aptitude for the sciences that his uncle, a religious of the order of the Camaldolesi, sent him to Rome in 1626 for the purpose of study. There he fell in with Castelli, the favorite pupil of Galileo, who instructed him in the work of the master on the laws of motion. Torricelli showed his thorough understanding by writing a thesis on the path of projectiles. Castelli sent this essay in manuscript to Galileo with strong recommendations of his young friend. Galileo invited Torricelli to his house but for personal reasons he was unable to accept until three months before the death of the blindscientist (1641). The grand duke prevailed upon him to remain at Florence and to succeed Galileo at the Academy. He solved some of the great mathematical problems of the day, such as the finding of the area and the centre of gravity of thecycloid
In 1641, Evangelista Torricelli moved to Florence to assist the astronomer Galileo. Then in 1644 in Florence Torricelli performed the famous experiment of “argento vivo” (quicksilver i.e. mercury). He filled a glass tube, open at one end, with mercury. Then, closing off the open end with a finger, he tipped the tube upside down and lowered it into a basin containing more mercury. By observing that the height of a mercury column in one-sided glass tubes, was independent of the shape and inclination of the tubes, he concluded that the column of mercury only descended partially, stopping at a height of around 76 cm.
Torricelli proclaimed that the space created by the descent of the mercury in the tube was empty, and that what held up the column of mercury depended on the pressure that the air exerted on the mercury in the basin. In 1644 Torricelli declared that his experiment proved two fundamental concepts: that nature did not abhor the void, and that the air had weight. The results of the mercury experiment opened a period of revolutionary transformations and forced a fresh look at a doctrine which had been in force for centuries.
Later generations of scientists, most notably Blaise Pascal, developed the barometer further.

"Being" opposed to "Not being"

For Greek Philosophers opposed 'being' was opposed to 'not being'. Change was impossible, because it would mean that something that was 'not being' changed into 'being', which was considered absurd. As explained by Hegel, in his lectures on Greek Philosophy, being and non-being, as something thought, which, when represented for consciousness as differing in regard to one another, are the plenum and the vacuum, have no diversity in themselves; for the plenum has likewise negativity in itself; as independent, it excludes what is different; it is one and infinitely many ones, while the vacuum is not exclusive, but pure continuity.

In particular Parmenides postulated that a void, essentially what is now known as a vacuum, in nature could not occur. This view was supported by Aristotle, Al-Farabi, Hobbes, Descartes, Leibniz, Maupertius, Kant, Birkeland and others, but was criticized by Leucippus, Hero of Alexandria, Ibn al-Haytham and others.

The atomic ideas of Leucippus and Democritus around 440 BC were opposed by Aristotle about 100 years or so later. But the atom and the vacuum are not things of experience; Leucippus says that are not the senses through which we become conscious of the truth.

Democritus asserted that space, or the Void, had an equal right with reality, or Being, to be considered existent. He conceived of the Void as a vacuum, an infinite space in which moved an infinite number of atoms that made up Being. These atoms are eternal and invisible; absolutely small, so small that their size cannot be diminished; absolutely full and incompressible, as they are without pores and entirely fill the space they occupy; and homogeneous, differing only in shape, arrangement, position, and magnitude.

With this as a basis to the physical world, Democritus could explain all changes in the world as changes in motion of the atoms, or changes in the way that they were packed together. This was a remarkable theory which attempted to explain the whole of physics based on a small number of ideas and also brought mathematics into a fundamental physical role since the whole of the structure proposed by Democritus was quantitative and subject to mathematical laws.

There are then questions for Democritus to answer. Where do qualities such as warmth, colour, and taste fit into the atomic theory? To Democritus atoms differ only in quantity, and all qualitative differences are only apparent and result from impressions of an observer caused by differing configurations of atoms. The properties of warmth, colour, taste are only by convention - the only things that actually exist are atoms and the Void.

Democritus's philosophy contains an early form of the conservation of energy. In his theory atoms are eternal and so is motion. Democritus explained the origin of the universe through atoms moving randomly and colliding to form larger bodies and worlds. There was no place in his theory for divine intervention. Instead he postulated a world which had always existed, and would always exist, and was filled with atoms moving randomly. Vortex motions occurred due to collisions of the atoms and in resulting vortex motion created differentiation of the atoms into different levels due only to their differing mass. This was not a world which came about through the design or purpose of some supernatural being, but rather it was a world which came about through necessity, that is from the nature of the atoms themselves.

“The full is nothing simple, for it is an infinitely manifold. These infinitely many, move in the vacuum, for the vacuum exists; their conglomeration brings about origination”, “disintegration and separation result in passing away.” “Activity and passivity subsist in the fact, that they are contiguous; but their contiguous not their becoming one, for from that which is truly”; “one there does not come a number, nor from that which is truly many, one.” Or, it may be said, they are in fact neither passive nor active, “for they merely abide through the vacuum” without having as their principle, process. Atoms thus are, even in their apparent union in that which we call things, separated from one another through the vacuum which is purely negative and foreign to them, i.e. their relation is not inherent in themselves, but is with something other than them, in. which they remain what they are. This vacuum, the negative in relation to the affirmative, is also the principle of the movement of atoms; they are so to speak solicited by the vacuum to fill up and to negate it.

Hero of Alexandria then in 150 A.D. made use of atoms to explain compression and rarefaction. Hero denied the existence of an extended vacuum, but allowed for a vacuum between atoms. One proof he cited was that fire could enter into a material, showing that it had openings, i.e., a vacuum. He pointed out that the pores of a diamond were too small to let in fire and so the stone was incombustible.

Naturae horror Vacui

What is nothing?
Greeks began to conceive of the cosmos as being made up of matter and its opposite, nothing. They then began to worry about the nature of nothing.

Horror Vacui is a theory first proposed by Aristotle based on the assumption that nature abhors vacuum, and therefore empty space would always be trying to suck in gas or liquids to avoid being empty.

Aristotle held that there are two kinds of motion for inanimate matter, natural and unnatural. Unnatural (or “violent”) motion is when something is being pushed, and in this case the speed of motion is proportional to the force of the push. Natural motion is when something is seeking its natural place in the universe, such as a stone falling, or fire rising.

For the natural motion of heavy objects falling to earth, Aristotle asserted that the speed of fall was proportional to the weight, and inversely proportional to the density of the medium the body was falling through. He did also mention that there was some acceleration, as the body approached more closely its own element, its weight increases and it speeds up. Although not quantitative, Aristotle was right. Indeed the ultimate asymptote of exact zero pressure is impossible to obtain. Modern theory states that the absolute vacuum is unstable and even that the "vacuum is more full than the plenum"