A fine and rare 19th-Century heliostat,

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Details

A fine and rare 19th-Century heliostat,
signed A. PRAZMOWSKI. 1, RUE BONAPARTE, PARIS, in a mahogany carrying case -- 20.3cm. (8in.) high

See Illustrations

The instrument is mounted on a concave triform ebonised metal base, with three adjustable screw feet. A circular brass plate with a pierced centre is mounted on the base, with two bubble levels. The heliostat is mounted between two tapering brass uprights, one of which has a pierced vertical quadrant, ungraduated, mounted on the inside, with screw clamp. The 8.9cm. (3½in.) diameter enamelled dial bears the maker's details and is graduated around three-quarters of the circumference IV-XII, I-VIII with ten-minute subdivisions. A subsidiary minute dial is unlabelled, with a brass index and one-minute subdivisions. The brass drum of the heliostat houses the mechanism, with a winding key beneath. Mounted in the centre of the dial is the analemma indicator, comprising a brass bar with uprights at either end, one with a pinhole sight, and the other with the analemma on an enamel face. On the cross bar at the base of the sight arm is a small circular aperture with a blued-steel index to read off the hour scale. The octagonal mirror is mounted in the centre on a threaded split sleeve with a knurled tightening wheel. When the instrument is not in use, the dial is covered by a heavy brass cap with a turned ivory handle. Also in the case are three tapering brass feet and a large table-standing bull's eye condensor. The case has a steel carrying handle and key, and an old inventory label on the side.

Literature

MILLS, A.A., "Heliostats, Siderostats, and Coelostats: A Review of Practical Instruments for Astronomical Applications" in Journal of the British Astronomical Association 95, 3 (1985) pp.89-98
--, "Portable Heliostats (Solar Illuminators)" in Annals of Science 43 (1986) pp.369-406

Special notice

No VAT will be charged on the hammer price, but VAT at 17.5% will be added to the buyer's premium which is invoiced on a VAT inclusive basis

Lot Essay

A heliostat is an instrument designed to capture a reflection of the Sun (or other celestial body) over a period of time, by rotating a clockwork mirror to match the Sun's apparent path through the sky. Prior to the advent of high-powered electric lights, this would be the most efficient way of providing sustained and adequate illumination for microscopy, or study of the sun itself and the properties of its beams. Their construction and refinement flourished in the second half of the nineteenth century, but by the start of the twentieth, and the advent of the electric light, they had become more or less obsolete. The coelostat (in which the moving mirror is arranged to produce a non-rotating image of the celestial body under examination) was invented by E.F. August in 1839; the heliostat was developed by O. von Littrow (1863) after August's design, and by Prazmowski (1877), who gave no credit to any previous inventor. His 1877 model was illustrated in the Nachet trade catalogue of 1910.

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