Tuesday, September 23, 2014

Hippolyte Fizeau and the Speed of Light

Hippolyte Fizeau (1819-1896)
photo: Charles Reutlinger, Académie des Sciences,
Smithsonian Institution Libraries
On September 23, 1819, French physicist Armand Hippolyte Louis Fizeau was born. He is well known for his calculation of the speed of light and his suggestion to use length of a light wave be used as a length standard.

Hippolyte Fizeau was born in Paris as the eldest son of Béatrice and Louis Fizeau, who was professor of Pathology at the Paris Medical School. He attended the prestigious Collège Stanislas in Paris where he became a friend with one of his fellow students, Léon Foucault. In September 1839. Famous Louis Daguerre put on a free course on his new photographic techniques in Paris and the two friends Fizeau and Foucault attended. They watched Daguerre expose a plate in a camera pointing out the window, then after talking about his process for about 30 minutes, he developed the plate using a variety of chemicals to reveal the picture. Although Fizeau and Foucault were impressed they also realised the limitations of the process - it would be wonderful to be able to take portraits, they thought, but the subject could not be expected to remain motionless for 30 minutes. After the course ended they began to experiment to try to speed up the process. [1]

Fizeau entered the Paris Medical School in 1840, but he soon gave up on medicine because of severe migraines and spent some time travelling during which time he regained his health. His new focus of attention should be physics. He attended Arago's lectures at the Observatory, and enrolled in a course on optics at the Collège de France. Furthermore, he began to deeply study notebooks containing the lecture notes taken by his brother who attended courses at the École Polytechnique. It was Arago, who encouraged Fizeau and Foucault in 1845 and suggested that they might attempt to make photographs of an image of the sun produced by a telescope. Thus, Fizeau and Foucault produced what is considered the first astronomical photography.

It was in the field of optics that Fizeau earned a lasting reputation. The original inspiration came from François Arago, who looked for a decisive test between the corpuscular and wave theories of light. If the wave theory was true, the velocity of light had to be greater in moving media, such as water flowing in a tube. The project implied the working out of a terrestrial method of measuring the speed of light, and Arago suggested that this could be done by using a rotating mirror.[2] In 1849, Fizeau calculated a value for the speed of light more precise than the previous value determined by Ole Rømer in 1676. He used a beam of light reflected from a mirror eight kilometers away. The beam passed through the gaps between teeth of a rapidly rotating wheel. The speed of the wheel was increased until the returning light passed through the next gap and could be seen.

Fizeau calculated the speed of light to be 313,300 kilometres per second, which was within about five percent of the correct value (299,792.458 kilometers per second). Fizeau published the first results obtained by his method for determining the speed of light in 1849. In 1851 he carried out a series of experiments in an attempt to detect the luminiferous ether—a hypothetical material that was thought to occupy all of space and to be necessary for carrying the vibrations of light waves. The experimental results failed to demonstrate the existence of the ether, but his work helped lead to the discarding of the ether theory in the early years of the 20th century.[3] Fizeau was elected a member of the Academy of Sciences in 1860, an a member of the Bureau des Longitudes in 1878. He received the decoration of the Legion of Honour in 1849 and became officer in 1875. In 1866 the Royal Society of London awarded him the Rumford Medal.

At yovisto you can learn more about the physics behind the speed of light in the NASA documentary 'Einsteins Cosmic Speed Limit'.

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Monday, September 22, 2014

William Playfair and the Beginnings of Infographics

Playfair's trade-balance time-series chart, from The Commercial and Political Atlas and Statistical Breviary, 1786
On September 22, 1759, Scottish engineer and political economist William Playfair was born. He is generally considered the founder of graphical methods of statistics. William Playfair invented four types of diagrams: line graph, bar chart, pie chart, and circle graph.

Playfair was born in 1759 in Scotland during the Enlightenment, a Golden Age in the arts, sciences, industry and commerce. He was the fourth son of the reverend James Playfair of the parish of Liff & Benvie near the city of Dundee in Scotland. His notable brothers were architect James Playfair and John Playfair, Professor of Mathematics and later Professor of Natural Philosophy at the University of Edinburgh. His father died in 1772 when William was 13, leaving the eldest brother John to care for the family and his education. His early taste for mechanics prompted his friends to place him as apprentice to a mill-wright Andrew Meikle, the inventor of the threshing machine. But, this is were William Playfair's multifaceted career should only start. He was in turn a millwright, engineer, draftsman, accountant, inventor, silversmith, merchant, investment broker, economist, statistician, pamphleteer, translator, publicist, land speculator, convict, banker, ardent royalist, editor, blackmailer and journalist.

In 1780, he went to England, was engaged as draftsman and personal assistant of the inventor James Watt at the steam engine manufacturing works of Boulton & Watt in Birmingham in 1777, where he received a scientific and engineering training. Among the most useful of his mechanical efforts, was the unrequited discovery of the French telegraph, gathered from a few partial hints, and afterwards adapted by an alphabet of his own invention to British use. [1] On leaving Watt's company in 1782, he set up a silversmithing business and shop in London, which failed. In 1787 he moved to Paris, taking part in the storming of the Bastille two years later. He returned to London in 1793, where he opened a "security bank", which also failed. From 1775 he worked as a writer and pamphleteer and did some engineering work.

Playfair's main achievement lies primarily in his innovations in the presentation of quantitative information by means of graphs and charts. But, he was not the first to come up with the idea. Already in 1765, Joseph Priestley had created the innovation of the first timeline charts, in which individual bars were used to visualize the life span of a person to compare the life spans of multiple persons. These timelines directly inspired Wiliam Playfair's invention of the bar chart, which first appeared in his Commercial and Political Atlas, published in 1786. Actually, Playfair was driven to this invention by a lack of data. He had collected data about the import and export from different countries over the years, which he presented as line graphs. Because he lacked the necessary series data for Scotland, he graphed its trade data for a single year (1781) as a series of bars, one for each of Scotland's trading partners.[4]

Playfair's Pie Charts from The Commercial and Political Atlas and Statistical Breviary, 1786
Playfair, who argued that charts communicated better than tables of data, has been credited with inventing the line, bar, and pie charts. His time-series plots are still presented as models of clarity. Playfair first published The Commercial and Political Atlas in London in 1786. It contained 43 time-series plots and one bar chart, a form apparently introduced in this work. It has been described as the first major work to contain statistical graphs. Playfair's Statistical Breviary, published in London in 1801, contains what is generally credited as the first pie chart. He was the first to use hachure, shading, and color, thus incorporating elements of classification into the quantitative depiction. The quality and detail of his work was such that in the two centuries since there has been no appreciable improvement of his basic designs. [5]

After the Bourbon restoration in France, William Playfair returned to Paris, where he edited a journal called Galignani’s Messenger. He had to flee the country a second time when prosecuted for libel, and thereafter spent his time writing in London, where he died at the age of 64.[3] Playfair has invented a universal language useful to science and commerce alike and though his contemporaries failed to grasp the significance, he had no doubt that he had forever changed the way we would look at data. However, it took almost a century after his death before his invention was fully accepted. [5]

At yovisto you can learn more about the visualization of statistical data in the famous TED-talk of Prof. Hans Rosling on 'Let my dataset change your mindset'.

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Sunday, September 21, 2014

Juan de la Cierva and the Autogiro

Demonstration of Cierva C.6 autogiro at Farnborough, Oct. 1925
On September 21, 1895, Spanish civil engineer and aviation pioneer Juan de la Cierva y Codorníu was born. His most famous accomplishment was the invention in 1920 of the Autogiro, a single-rotor type of aircraft, a predecessor of today's helicopter.

Juan de la Cierva was born in Murcia, Spain to a wealthy family. Although trained as a civil engineer, Cierva became interested in aviation early in his youth. After several successful experiments with aviation as a boy, he eventually earned a civil engineering degree. For six years he attended the Escuela Especial de Ingenieros de Caminos, Canales y Puertos in Madrid, Spain, where he studied theoretical aerodynamics. Following this, he entered a competition to design military aircraft for the government and built a biplane bomber with an airfoil (the part of a plane that provides lift) that he designed mathematically. The plane was tested in May 1919, but it crashed when the pilot stalled it.[1]

Cierva believed that fixed-wing aircraft were unsafe, so he experimented with a rotary-wing design. In 1919 he started to consider the use of a rotor to generate lift at low airspeed, and eliminate the risk of stall. In order to achieve this, he utilized the ability of a lifting rotor to autorotate, whereby at a suitable pitch setting, a rotor will continue to rotate without mechanical drive, sustained by the torque equilibrium of the lift and drag forces acting on the blades. This phenomenon was already known, and was available as a safety feature to allow controlled descent of a helicopter in the event of engine failure. With De la Cierva's autogiro, the rotor was drawn through the air by means of conventional propeller, with the result that the rotor generated sufficient lift to sustain level flight, climb and descent.

Before this could be satisfactorily achieved, De la Cierva experienced several failures primarily associated with the unbalanced rolling movement generated when attempting take-off, due to dissymmetry of lift between the advancing and retreating blades. This major difficulty was resolved by the introduction of the flapping hinge. In 1923, De la Cierva's first successful Autogiro was flown in Spain. In a fixed-wing aircraft, lift is provided by the wing, thrust by the propeller. Cierva, though, believed that the autogiro controlled these forces better than fixed-wing aircraft, which had a tendency in those days to stall, or lose lift suddenly. He also wanted to develop an aircraft that needed only a short takeoff run and could slowly land in small areas. The autogiro was a major step toward those goals.[1]

In 1925, he demonstrated his autogiro to the British Air Ministry at Farnborough, Hampshire, which was a great success, and resulted in an invitation to continue the work in the UK. The same year, de la Cierva moved to England where, with the support of Scottish industrialist James G. Weir, he established the Cierva Autogiro Company. On September 18, 1928, he flew one of his autogiros (C.8) across the English Channel, and in 1930, he flew one from England to Spain. As De la Cierva's autogiros achieved success and acceptance, others began to follow and with them came further innovation. Most important was the development of direct rotor control through cyclic pitch variation, achieved initially by tilting the rotor hub and subsequently by Raoul Hafner by the application of a spider mechanism that acted directly on each rotor blade. The introduction of jump take-off was another major improvement in capability. The rotor was accelerated in no-lift pitch until the rotor speed required for flight was achieved, and then declutched.

At the outbreak of the Spanish Civil War in 1936, de la Cierva supported the forces of Francisco Franco, while his brother was executed by the Republican army in Paracuellos del Jarama. In a very ironic twist of fate the man who spent the better part of his life to develop a safe aircraft would loose his own life in an aircraft accident. On the morning of 9 December 1936, de la Cierva boarded a Dutch DC-2 of KLM at Croydon Airfield, bound for Amsterdam, which during take off should stall and crash on the roof of a building at the end of the runway.[2] Autogiros were used during the 1930s for military liaison, mail delivery, and agricultural purposes. De la Cierva’s work on rotor dynamics and control made possible the modern helicopter, whose development as a practical means of flight had been prevented by these problems.

At yovisto you can learn more about the history of early helicopters in a short documentary produced for Encyclopedia Britannica, now part of the Prellinger archive on Helicopters from 1953.

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