The Porter SunClock shown above was purchased by me in Connecticut in July, 1998 right after attending Stellafane in Springfield, VT. The design is very unique in that it employs two optical elements (not shown), the first, a lens, is used to image the NCP (North Celestial Pole) and thereby align the polar axis shaft (held above the figurine) the second, a mirror, is used to image the Solar disk onto the Analemma. The mirror is mounted at a 45 degree angle to the polar axis shaft and thereby aligns the reference plane of the celestial equator at right angles to the polar axis. When the Sun is on the equator (the Equinoxes) the imaged rays will be parallel to the polar axis. The polar axis shaft alignment to the NCP is obviously done at night. To read the time a knob at the back of the SunClock, which drives the internal gear train, is turned until the image of the Sun's disk bisects the portion of the Analemma that corresponds to the current date. As such, the SunClock also functions as a rough calendar, being most accurate (to within a couple days) on dates close to the Equinoxes (when the declination rate is fastest) and the least accurate (to within several days) on dates close to the Solstices (when the declination rate is slowest). For the SunClock to display Standard Mean Time the time difference between the Local Meridian and the Standard Time Zone Meridian must be accounted for by adjusting (only once) the minute hand by the corresponding amount.
Only one other SunClock of this type is known by me to exist, it was reported to me by its previous owner to be incomplete, its current whereabouts are unknown. It was originally bought from Porter's daughter at Stellafane, however its operation remained unclear and it was never put into operation. I determined the functional design by careful consideration and by reading several of Porter's sundialing articles that appeared in Scientific American, one of which makes some mention of this unique design (although incorporated in a much different configuration). Both pieces were made by Porter himself while he lived in Pasadena, CA, my piece has this stamped on the dial plate, the other purchased from Porter's daughter does not, they were probably made sometime between 1935-1940. Lastly, this particular dial is not found in any of the records that I have seen at the Springfield ATM museum or within any other publications by or about Porter. It is clearly one of his best (if not the best) sundial designs and is by far the most technically involved and artistically interesting. Efforts to reproduce the Porter SunClock in bronze are already under way.