A rainbow is a meteorological phenomenon, caused by reflection and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. Rainbows can be full circles. However, the observer sees only an arc formed by illuminated droplets above the ground, centered on a line from the sun to the observer's eye. In a primary rainbow, the arc shows red on the outer violet on the inner side; this rainbow is caused by light being refracted when entering a droplet of water reflected inside on the back of the droplet and refracted again when leaving it. In a double rainbow, a second arc is seen outside the primary arc, has the order of its colours reversed, with red on the inner side of the arc; this is caused by the light being reflected twice on the inside of the droplet before leaving it. A rainbow is not located at a specific distance from the observer, but comes from an optical illusion caused by any water droplets viewed from a certain angle relative to a light source.

Thus, a rainbow can not be physically approached. Indeed, it is impossible for an observer to see a rainbow from water droplets at any angle other than the customary one of 42 degrees from the direction opposite the light source. If an observer sees another observer who seems "under" or "at the end of" a rainbow, the second observer will see a different rainbow—farther off—at the same angle as seen by the first observer. Rainbows span a continuous spectrum of colours. Any distinct bands perceived are an artefact of human colour vision, no banding of any type is seen in a black-and-white photo of a rainbow, only a smooth gradation of intensity to a maximum fading towards the other side. For colours seen by the human eye, the most cited and remembered sequence is Newton's sevenfold red, yellow, blue and violet, remembered by the mnemonic Richard Of York Gave Battle In Vain. Rainbows can be caused by many forms of airborne water; these include not only rain, but mist and airborne dew. Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind the observer at a low altitude angle.

Because of this, rainbows are seen in the western sky during the morning and in the eastern sky during the early evening. The most spectacular rainbow displays happen when half the sky is still dark with raining clouds and the observer is at a spot with clear sky in the direction of the sun; the result is a luminous rainbow. During such good visibility conditions, the larger but fainter secondary rainbow is visible, it appears about 10° outside of the primary rainbow, with inverse order of colours. The rainbow effect is commonly seen near waterfalls or fountains. In addition, the effect can be artificially created by dispersing water droplets into the air during a sunny day. A moonbow, lunar rainbow or nighttime rainbow, can be seen on moonlit nights; as human visual perception for colour is poor in low light, moonbows are perceived to be white. It is difficult to photograph the complete semicircle of a rainbow in one frame, as this would require an angle of view of 84°. For a 35 mm camera, a wide-angle lens with a focal length of 19 mm or less would be required.

Now that software for stitching several images into a panorama is available, images of the entire arc and secondary arcs can be created easily from a series of overlapping frames. From above the earth such as in an aeroplane, it is sometimes possible to see a rainbow as a full circle; this phenomenon can be confused with the glory phenomenon, but a glory is much smaller, covering only 5–20°. The sky inside a primary rainbow is brighter than the sky outside of the bow; this is because each raindrop is a sphere and it scatters light over an entire circular disc in the sky. The radius of the disc depends on the wavelength of light, with red light being scattered over a larger angle than blue light. Over most of the disc, scattered light at all wavelengths overlaps, resulting in white light which brightens the sky. At the edge, the wavelength dependence of the scattering gives rise to the rainbow. Light of primary rainbow arc is 96% polarised tangential to the arch. Light of second arc is 90% polarised.

A spectrum obtained using a glass prism and a point source is a continuum of wavelengths without bands. The number of colours that the human eye is able to distinguish in a spectrum is in the order of 100. Accordingly, the Munsell colour system distinguishes 100 hues; the apparent discreteness of main colours is an artefact of human perception and the exact number of main colours is a somewhat arbitrary choice. Newton, who admitted his eyes were not critical in distinguishing colours divided the spectrum into five main colours: red, green and violet, he included orange and indigo, giving seven main colours by analogy to the number of notes in a musical scale. Newton chose to divide the visible spectrum into seven colours out of a belief derived from the beliefs of the ancient Greek sophists, who thought there was a connection between the colours, the musical notes, the known objects in the Solar System, the days of the week. Scholars have noted that what Newton regarded at the time as "blue" would today be regarded as cyan, what Newton called "indigo" would today be considered blue.

According to Isaac Asimov, "It is customary to list indigo as a colour lying between blue and violet, but it ha

Niederwald is a former municipality in the district of Goms in the canton of Valais in Switzerland. On 1 January 2017 the former municipalities of Niederwald, Grafschaft, Münster-Geschinen and Reckingen-Gluringen merged into the new municipality of Goms. Niederwald is first mentioned in 1526 as Zniderwaldt. Niederwald has an area, as of 2011, of 4.7 square kilometers. Of this area, 34.8 % is used for agricultural purposes. Of the rest of the land, 3.0% is settled and 18.4% is unproductive land. The municipality is located above the Fiesch valley and along the old highway which ran from Ernen over the Rhone bridge to the right side of the valley, it consists of the former hamlet of Rottenbrigge. The blazon of the municipal coat of arms is Or, on Coupeaux Vert three Pine trees of the same trunked proper, a Chief Azure. Niederwald has a population of 45; as of 2008, 6.8% of the population are resident foreign nationals. Over the last 10 years the population has changed at a rate of -47.5%. It has changed at a rate of -10 % due to births and deaths.

Most of the population speaks German as their first language, French is the second most common and Serbo-Croatian is the third. As of 2008, the gender distribution of the population was 50.3 % female. The population was made up of 27 non-Swiss men. There were 26 non-Swiss women. Of the population in the municipality 39 or about 55.7% were born in Niederwald and lived there in 2000. There were 19 or 27.1% who were born in the same canton, while 5 or 7.1% were born somewhere else in Switzerland, 7 or 10.0% were born outside of Switzerland. The age distribution of the population is children and teenagers make up 18.6% of the population, while adults make up 58.6% and seniors make up 22.9%. As of 2000, there were 27 people who never married in the municipality. There were 4 widows or widowers and individuals who are divorced; as of 2000, there were 33 private households in the municipality, an average of 2.1 persons per household. There were 12 households that consist of 1 households with five or more people.

Out of a total of 33 households that answered this question, 36.4% were households made up of just one person. Of the rest of the households, there are 11 married couples without children, 9 married couples with children There was 1 household, made up of unrelated people. In 2000 there were 30 single family homes out of a total of 46 inhabited buildings. There were 5 multi-family buildings, along with 7 multi-purpose buildings that were used for housing and 4 other use buildings that had some housing. In 2000, a total of 32 apartments were permanently occupied, while 24 apartments were seasonally occupied and 3 apartments were empty; the historical population is given in the following chart: It was home to famous hotelier César Ritz, buried in the local cemetery. The entire village of Niederwald is designated as part of the Inventory of Swiss Heritage Sites In the 2007 federal election the most popular party was the CVP which received 75.3% of the vote. The next three most popular parties were the FDP and the Green Party.

In the federal election, a total of 24 votes were cast, the voter turnout was 53.3%. In the 2009 Conseil d'Etat/Staatsrat election a total of 22 votes were cast, of which or about 0.0% were invalid. The voter participation was 61.1%, much more than the cantonal average of 54.67%. In the 2007 Swiss Council of States election a total of 24 votes were cast, of which or about 0.0% were invalid. The voter participation was 58.5%, similar to the cantonal average of 59.88%. As of 2010, Niederwald had an unemployment rate of 0.5%. As of 2008, there were 2 people employed in the primary economic sector and about 1 business involved in this sector. 24 people were employed in the secondary sector and there were 2 businesses in this sector. 3 people were employed with 1 business in this sector. There were 35 residents of the municipality who were employed in some capacity, of which females made up 45.7% of the workforce. In 2008 the total number of full-time equivalent jobs was 27; the number of jobs in the primary sector was 2.

The number of jobs in the secondary sector was 22 of which 21 or were in manufacturing and 1 was in construction. The number of jobs in the tertiary sector was 3. In the tertiary sector all 3 were in a restaurant. In 2000, there were 39 workers who commuted into 18 workers who commuted away; the municipality is a net importer of workers, with about 2.2 workers entering the municipality for every one leaving. Of the working population, 17.1% used public transportation to get to work, 37.1% used a private car. From the 2000 census, 65 or 92.9% were Roman Catholic, while or 0.0% belonged to the Swiss Reformed Church. Of the rest of the population, there were 2 members of an Orthodox church. 3 belonged to no church, are atheist. In Niederwald about 28 or of the population have completed non-mandatory upper secondary education, 3 or have completed additional

Henry Tracey Coxwell was an English aeronaut and writer about ballooning active over the British Isles and continental Europe in the mid-to late nineteenth century. His achievements included having established and led two military balloon companies on Cologne, Germany at the outbreak of the Franco-Prussian war broke, leading the first aerial trip in England for purposes of photography, piloting a British Association for the Advancement of Science flight from Wolverhampton, England that achieved a record altitude, as well as founding The Balloon, or Aerostatic Magazine, collecting his experiences in an autobiography, My Life and Balloon Experiences, he was referred to as the foremost balloonist of the last half of the nineteenth century by the English-language periodical, Illustrated London News, in January 1900. Henry Tracey Coxwell was born at the parsonage at Wouldham, Kent, on 2 March 1819, he was the youngest son of Commander Joseph Coxwell of the Royal Navy, grandson of the Rev. Charles Coxwell of Ablington House, Gloucestershire.

He went to school at Chatham, where his family moved in 1822, in 1836 he was apprenticed to a surgeon dentist. As a boy he became interested in balloons, he spared no efforts to witness as many ascents as possible; the successful voyage of Green's balloon from Vauxhall Gardens to Germany stimulated his enthusiasm, but it was not until 19 August 1844, at Pentonville, that he had an opportunity of making an ascent. In the autumn of 1845 he founded and edited The Balloon, or Aerostatic Magazine, of which about twelve numbers were printed at irregular intervals. In 1847 he made a night flight from Vauxhall Gardens with Albert Smith during a storm: a 16 ft rent appeared in the envelope, the balloon fell to earth, the occupants being saved by the balloon catching on some scaffolding before hitting the ground. Undeterred, Coxwell made another flight the following week. Coxwell became a professional balloonist in 1848, when he was entrusted with the management of a balloon, the Sylph, in Brussels, subsequently made ascents at Antwerp, Elberfeld and Johannisberg in Prussia.

At Hanover, in the summer of 1850, he had a narrow escape, owing to the proximity of lofty trees, during this year and the next he took up many passengers at Berlin, Vienna and elsewhere. In 1852 he returned to London and made ascents from Cremorne Gardens, the New Globe Gardens in the Mile End Road and the Pavilion Gardens in Woolwich. In September 1854 he made some demonstrations in signalling from a balloon at Surrey Gardens. In 1862 the British Association for the Advancement of Science determined to make investigations of the upper atmosphere using balloons. Dr. James Glaisher, FRS, was chosen to carry out the experiments, at the suggestion of Charles Green, Coxwell was employed to fly the balloons. Coxwell constructed a 93,000 cu ft capacity balloon named the Mammoth, on 5 September 1862, taking off from Wolverhampton and Glaisher reached the greatest height achieved to date. Glaisher lost consciousness during the ascent, his last barometer reading indicating an altitude of 29,000 ft and Coxwell lost all sensation in his hands, but managed just in time to pull the valve-cord with his teeth before losing consciousness.

The balloon dropped nineteen thousand feet in fifteen minutes. Calculations estimated their maximum altitude at 35,000 to 37,000 ft. In 1863 Coxwell made a demonstration of ballooning to the Army at Aldershot; these had little practical outcome, although the War Office did order a balloon from Coxwell with the intention of shipping it to Ghana for use in the Third Anglo-Ashanti War. However, the practicalities of supplying hydrogen under field conditions resulted in the cancellation of the project. In 1863, in company with Henry Negretti, Coxwell made the first aerial trip in England for purposes of photography. In 1864-1865, in the Research, he made some successful ascents in Ireland, gave some lectures upon aerostation. In 1864 his balloon, was destroyed during the Leicester balloon riot; when the Franco-Prussian war broke out in 1870 he went to manage some war-balloons for the Germans. He formed two companies, two officers, forty-two men, at Cologne, his assistant went on to Strasbourg, but the town surrendered before much service was rendered.

On 17 June 1885, he made his last ascent in the City of York. He had made an annual display at York for several years, there he bade farewell to a profession of which he had been one of the most daring exponents for over forty years, his immunity from serious accidents was due to his instinctive prudence, but still more to his thorough knowledge of ballooning tackle. Coxwell had a balloon factory in Sussex. After his retirement, Coxwell lived for a time at Tottenham, but moved to Seaford, East Sussex, he died on 5 January 1900, in Lewes, England. He has a memorial at St Peter's Church, East Blatchington, Seaford. During 1887-1889 Coxwell collected together in two volumes a number of interesting but ill-arranged and confusing chapters upon his career as an aeronaut, to which he gave the title My Life and Balloon Exper