Showing posts with label Storia della scienza. Show all posts
Showing posts with label Storia della scienza. Show all posts

Friday 24 May 2013

A liquid telescope

http://en.wikipedia.org/wiki/Liquid_mirror_telescope

Liquid mirror telescopes are telescopes with mirrors made with a reflective liquid. The most common liquid used is mercury. The container for the liquid is rotating so that the liquid assumes a paraboloidal shape. A paraboloidal shape is precisely the shape needed for the primary mirror of a telescope. The rotating liquid assumes the paraboloidal shape regardless of the container's shape.  Liquid mirrors can be a low cost alternative to conventional large telescopes. Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid metal mirror is much less expensive to manufacture.

"Isaac Newton noted that the free surface of a rotating liquid forms a circular paraboloid and can therefore be used as a telescope, but he could not actually build one because he had no way to stabilize the speed of rotation[citation needed] (the electric motor did not exist yet). The concept was further developed by Ernesto Capocci of the Naples Observatory (1850), but it was not until 1872 that Henry Skey of Dunedin, New Zealand constructed the first working laboratory liquid mirror telescope."

"Another difficulty is that a telescope with a liquid metal mirror can only be used in zenith telescopes that look straight up at the zenith, so it is not suitable for investigations where the telescope must remain pointing at the same location of space ... Currently, the mercury mirror of the Large Zenith Telescope in Canada is the largest liquid metal mirror in operation. It has a diameter of six meters, and rotates at a rate of about 8.5 revolutions per minute."

Saturday 22 September 2012

The world's first seismometer was Chinese


Who was the inventor of the first siesmometer?
 Zhang Heng. He was  (AD 78–139) a Chinese astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman. He lived under the Han Dynasty (AD 25–220) of China. He was a  Chief Astronomer, Prefect of the Majors for Official Carriages, and then Palace Attendant at the imperial court.  He invented the world's first water-powered armillary sphere,  improved the inflow water clock by adding another tank and invented the world's first seismometer, which discerned the cardinal direction of an earthquake 500 km away. He improved previous Chinese calculations of the formula for pi. In addition to documenting about 2,500 stars in his extensive star catalogue. Some modern scholars have also compared his work in astronomy to that of Ptolemy (AD 86–161). (Adapted from Wiki)

 A replica of an ancient Chinese Siesmograph  (25-220 CE). Picture taken in July 2004  at Chabot Space & Science Center in Oakland California.
"In 132 CE, after several serious earthquakes in China, astronomer Zhang Heng invented this instrument to warn people of the next one. When the ground shook, it moved a pendulum inside the jug. The pendulum pushed a lever that opened one dragon's mouth. A ball rolled out and into the toad's mouth below, sounding an alarm. The open dragon mouth pointed in the direction of the earthquake, notifying the Emperor."
http://en.wikipedia.org/wiki/File:EastHanSeismograph.JPG