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Scaphe vs. Hemicyclium

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Two of a kind


The scaphe and hemicyclium each do an excellent job of imaging the celestial sphere in microcosm, arguably more intuitively that planar dials. As the sun traces its course through the sky, a nodus traces a mirroring path along the inner surface of these dials. Peering into one reveals a microcosm of the sky, flipped upside down so as to catch the sun's shadow.


...but which is which? Confusion on this topic arises not infrequently; I would like to offer a distinction to hopefully set the record straight.


Before defining these dials, I first clarify: though these terms tend to be associated with European sundials, similar concepts were developed abroad–case in point this Korean scaphe.



The scaphe


The defining feature of the scaphe is its hemispherical dial surface. The dial itself constitutes a hollowed half-sphere often carved. Curving hour lines are inscribed along the inside of this spherical cavity, and the dial's nodus may either sprout from a horizontal or vertical position. If vertical, the nodus' base sits at the nadir–the point directly opposite the observer on the celestial sphere (opposite of the zenith, which is the point directly overhead).


The most common identifying term for this type of dial is Latinized from the Greek "skaphe." The Latin "hemispherium" is also used on occasion.




The hemicyclium


Similar to the scaphe, the hemicyclium exists as a spherical hollow often carved into stone. However, it features less material–the portion of the sphere below the tropic of cancer is cleaved away.


Because the nodus' shadow only reaches as low as the tropic of cancer, cutting away this unengraved material allows the dial to more easily read. Unlike the scaphe, the hemicyclium can be read from a vantage point lower than the dial itself (see Pompeii's hemicyclium sitting atop a column).


By necessity, the nodus of the hemicyclium is set at a horizontal position–the nadir of the celestial sphere is cut away and thus unable to support it.



Into the pocket


In addition to these stationary forms, the scaphe (decidedly not the hemicyclium) may be found incorporated into portable dials (albeit utilizing more shallow hollows). Most often used in the context of diptychs, scaphae are ideally suited for carrying Italian hours, Babylonian hours, or an overlay of both.


Particularly on Nuremberg diptychs, scaphae may be added as smaller, secondary (and/or tertiary) dials displaying these additional hour systems.



While the seasonal hour is the system most often associated with the scaphe and hemicyclium, this three-dimensional dial construction is well-suited for a variety of contexts and appears with great frequency in collections of all sizes.


An additional drawback of the scaphe
An additional drawback of the scaphe


Evan Boxer-Cook

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