- Heliometer
Heliometer (from Greek "sun" and "measure") is an instrument originally designed for measuring the variation of the
sun 's diameter at differentseason s of the year, but applied now to the modern form of the instrument which is capable of much wider use. The present article also deals with other forms of double-imagemicrometer .To sum up briefly the history of the development of the heliometer, the first application of the divided object-glass and the employment of double images in astronomical measures is due to
Servington Savary from Exeter in 1743.Pierre Bouguer , in 1748, originated the true conception of measurement by double image without the auxiliary aid of afilar micrometer , that is by changing the distance between two object-glasses of equal focus.John Dollond , in 1754, combined Savary's idea of the divided object-glass with Bouguer's method of measurement, resulting in the construction of the first really practical heliometers. As far as we can ascertain,Joseph von Fraunhofer , some time not long before 1820, constructed the first heliometer with an achromatic divided object-glass, i.e. the first heliometer of the modern type.References
*1911
*Willach, Rolf. "The Heliometer: Instrument for Gauging Distances in Space." Journal of the Antique Telescope Society, number 26, pp. 5-16 (2004).External links
* [http://kuffner-sternwarte.at/sternwarte/vks_ksw_instr1.html#helio Photos from the largest heliometer in the world (Kuffner-Obervatory, Vienna)]
Wikimedia Foundation. 2010.