Heliometer
From Wikipedia, the free encyclopedia
Heliometer (from Greek sun and measure) is an instrument originally designed for measuring the variation of the sun's diameter at different seasons 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-image micrometer.
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. To Pierre Bouguer in 1748 is due the true conception of measurement by double image without the auxiliary aid of a filar micrometer, viz. by changing the distance between two object-glasses of equal focus. To John Dollond in 1754 we owe the combination of Savary's idea of the divided object-glass with Bouguer's method of measurement, and the construction of the first really practical heliometers. To Joseph von Fraunhofer, some time not long previous to 1820, is due, so far as we can ascertain, the construction of the first heliometer with an achromatic divided object-glass, i.e. the first heliometer of the modern type.
[edit] References
- This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
- Willach, Rolf. "The Heliometer: Instrument for Gauging Distances in Space." Journal of the Antique Telescope Society, number 26, pp. 5-16 (2004).
