Unusual and rare (possibly unique) scientific measuring device comprised of a painted, incised, and calibrated plaster half sphere in rectangular box with removable lid. A printed paper horizon surrounds the sphere. The outer ring of measurements on the horizon mark the degrees from 0 to 180 on each side. The inner ring of measurements intersects the meridian line at 45 degrees. The corners of the horizon on one side are labeled “Pl. S. Convexes” and “Elev. S. Convexes,” and on the other side “Pl. S. Concaves” and “Elev. S. Concaves.” (“Elev.” presumably refers to elevation).
Approximately half the sphere is yellow, the rest is green. Inscribed lines (concentric but irregular) divide the surface into sections, each of which is numbered. The first circle on the yellow side is numbered “0,” the rest in succession are marked with Roman numerals (I, II, III, IV, V, VI). Two of the sections on the green side have inscribed lines with visible numbers, IV and V, which follow the same order as the yellow side (number increases as it gets closer to the circumference). Another line, with two rings of numbers, is inscribed into the surface around the circumference, perpendicular to the others. This line is aligned with an arrow printed on horizon, labeled “Merid.” (presumably meridian) and corresponds to the outer ring scale of 0 degrees at the arrow’s tail and 180 degrees at its head.
The half sphere is the top section of a continuous (and removable) plaster block, the bottom of which rests hidden inside the lower portion of the box. On the underside of the plaster is inscribed "Skiographe," discussed below. It is also inscribed in block letters "Chretien," which translates as “Christian,” and is probably someone’s name. An inscription on the inside of the box lid indicates that it was made and sold in Lagny-le-sec, in northern France, and also sold by a M. Cousinet in Paris: “chez l’Auteur à Lagny-le-sec, par le Plessis-Belleville (Oise) et chez M. Cousinet 72 Rue Crozatier Paris.”
The word "skiographe" spelled with a “k” does not appear to have ever been an official French word and may have been coined by the maker as a name for this device. The only time it appears in French literature as far as can be determined is in reference to Apollodore le Skiographe, the French name for the ancient Greek painter Apollodorus Skiagraphos. However, the word “sciography” appears in 18th century literature in two contexts that might be relevant to this device. Ephraim Chambers’ 2-volume Cyclopædia, or, An Universal Dictionary of Arts and Sciences (1728) gives this definition: "Sciography, in Astronomy, &c. is a Term some Authors use for the Art of finding the Hour of the Day or Night, by the Shadow of the Sun, Moon, Stars, &c. See DIAL." Alternatively, the art historian Michael Baxandall explains that in 18th century France the “old mathematical discipline of sciography” was a sub-branch of linear perspective in which the artist produced “two dimensional renderings of the calculated forms of…projected shadows.” Baxandall further explains:
[Sciography] belongs to an important and highly institutionalized element in French technical culture. At the great new state schools of bridge and highway engineering, of mines, of naval architecture, of military science, and also at the proliferating craftsmen’s schools and free drawing schools, highly sophisticated modes of technical draughtsmanship were being taught, and they included very precise methods of shadow projection. … There were classes of activity for which serious sciography was necessary and productive: astronomy, particularly the observation of eclipses, some branches of optics and probably gnomonics. For surveying and for registering spatial relations in technical drawing of various kinds, precise shadow projection was a convenient resource (Baxandall pp. 84-85).
The actual function or purpose of this device has not as yet been determined. Based on the foregoing description and research it might have been designed to determine the location of shadows at different times of day (a 12-hour period) or different times of year (a 12-month period). This theory is favored inasmuch as the sphere is divided into 12 numbered sections. As such, the device could possibly assist with choosing an orientation for a building, designing a sundial, or teaching technical drawing, especially since it is small, portable, and has a built-in base that could be set on a board, desk or on the ground. We invite visitors to our website who are otherwise familiar with this unusual instrument to email us with any additional information.
Condition: Generally good with the usual overall toning, soiling, wear. Box a bit soiled and worn, but still intact.
Baxandall, Michael. Shadows and Enlightenment. Bath, UK: The Bath Press, 1995. pp. 84-85.
“Help Identify This Object -- Plaster Sphere In Box.” Various contributors. MapHist. 20 August - 12 September 2009 http://www.maphist.nl (12 September 2009).