Heliostat (detail)

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probably made in Dublin

Postcard of Heliostat (detail).
© National Museums Scotland

Heliostat (detail)

George Johnstone Stoney (1826-1911), whose most important work was the conception and calculation of the magnitude of the atom for which he proposed the name 'electron', designed a cheap compact direct-drive heliostat. It was manufactured from around 1880 by Yeates and Son of Dublin. This detail shows the makers' signature.

The description of how to use the heliostat is on the accompanying leaflet: wind up the clock in the base, set the arc to the latitude, stand the instrument level, set it due north and south, turn the Sun arm towards the Sun and adjust it so the rays pass through the little sight hole, forming a bright spot of light in the centre of the disc. Then turn the mirror to the direction required, and 'the adjustment will be complete'.

The first satisfactory solar telescope was attached to the heliostat developed by Leon Foucault (1819-1868), who invented the linkage which converted the steady motion of a clock into the complex motion needed to correct the variation in the Sun's position during the day. The heliostat mirror is flat, so that it does not focus the light, but reflects sunlight into a fixed solar telescope.

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Online ID: 000-180-001-221-C
Image Rights Holder: National Museums Scotland
Project: 0504: National Museums Scotland Part 2
Project description | View all records in project
Ref: National Museums Scotland  
Date: Around 1880
  • For Stoney, see C. Mollan, W. Davis, B. Finucane (eds.), Some People and Places in Irish Science and Technology (Dublin, 1985), 50-1. For Yeates & Son, see Mollan et al. (eds.) Some More People and Places in Irish Science and Technology (Dublin, 1990), pp 
  • Illustrated in J.E. Burnett and A.D. Morrison-Low, Vulgar & Mechanick: the Scientific Instrument Trade in Ireland 1650-1921 (Edinburgh and Dublin, 1989), 43. See also pp 39-46. 
  • The Stoney heliostat is discussed by A.A. Mills, 'Portable heliostats (solar illuminators)' Annals of Science 43 (1986), pp 399-401 
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