On 23 September 1819, Armand-Hippolyte-Louis Fizeau was born.
Fizeau was a French physicist best known for being the first to develop a reliable experimental method of determining the speed of light on Earth. The Danish astronomer, Ole Roemer, had made the first serious calculation of the speed of light in 1676. Roemer’s deduction was based upon his observations of the eclipses of Io, Jupiter’s first moon. However, it was not until 1849 that Fizeau, working closely with Foucault, directly measured the speed of light on Earth. Fizeau used a cogwheel and a mirror located several miles apart, which were set up to allow a pulsing light beam to pass between them. By rotating the cogwheel, Fizeau was able to observe the light beam passing between the cogs of the wheel to the distant mirror and then reflected back. If he spun the wheel fast enough, he was able to obscure the reflection. This meant that the reflected light beam struck a cog. Fizeau proposed that the time it took for the wheel to move the width of one cog must be equal to the time it takes for the light beam to travel to the mirror and back to strike the cog. Knowing the rotational speed of the cogwheel, the width of one cog, and the distance to the mirror, were all that was required for Fizeau to make the simple calculation of the speed of light. His calculation was very close to the current accepted value of the speed of light.
Starting with Ole Roemer’s 1676 breakthrough endeavours, the speed of light has been measured at least 163 times by more than 100 investigators utilizing a wide variety of different techniques. Finally in 1983, more than 300 years after the first serious measurement attempt, the speed of light was defined as being 299 792,458 kilometres per second by the Seventeenth General Congress on Weights and Measures. The metre is defined as the distance light travels through a vacuum during a time interval of 1/299 792 458 seconds. In general, however, (even in many scientific calculations) the speed of light is rounded to 300 000 kilometers (or 186 000 miles) per second.
Ealing Common is an area of open space which became prominent at the time of the enclosures of the late eighteenth century.
Ealing Common was consolidated after the purchase of the common land by the Ealing Local Board. The Common is a large area with avenues of horse chestnut trees, most of which were planted in the late Victorian period. Charles Jones was the Ealing borough surveyor and responsible for the nineteenth-century layout. The northern part of the common has a notably large oak tree as its highlight. London plane trees are also found with horse chestnuts around the perimeter of the common. Ealing Common station was opened on 1 July 1879 by the District Railway on a new extension from Turnham Green to Ealing Broadway. Between 1886 and 1910 the station was called Ealing Common and West Acton after which it changed to its current name.
Video: Flying into LCY
A simulated flight into LCY courtesy of Google Earth Studio.
TUM Dine With Me