A nocturnal with a month scale in two rings and divided into three days, placed around the central sighting hole. Within this is a volvelle cut with triangular teeth numbered 1-15 for the hours of darkness in the Italian hour reckoning which begins at sunset. Each hour is subdivided to twenty minutes. A second volvelle carrying the index arm is mounted above the hour dial. below is the punched inscription HOROLOGIUM. NOCTIS. AD. STELLAM. POLI. ET AD. DVAS. VLTIM. STE. URE. MA: (A night dial for the Pole star and the two guards of the Great Bear).
Engraved in the apex with a solar course diagram marked MOT[US] SO[L]IS and composed of three concentric arcs, the interior two with twelve divisions, the outer with twenty-four. The latter with the initial letters of the signs of the zodiac, the second with those of the months and the innermost with a sequence of numbers between 3 and 9. The three arcs used together offer a rapid means of find the degree and sign of the zodiac of the sun for any date of the year; (for a description of the method of use see Turner A, p. 10). The figure 14 placed above the scale is the latest date for the period that the sun can enter a new sign. Beneath this scale is the diagram for an altitude sundial in Italian hours (5-23) without sub-divisions, the morning hours being indicated by smooth lines, the afternoon hours by dotted lines and to each side are the two halves of the calendar scale requisite for its use. to the top right is the inscription QVADRANS. MENSORIUM, ET,DIEI. HORARIVM AD. ALTIT. POLI G. 43 (a quadrant for the months and hours of the day at the latitude of 43 degrees). The limb is marked with a degree scale reading to 90 degrees by 1 degree divisions numbered by groups of ten and with the corresponding shadow square.
Turner, Gerard l'E, 'The Florentine Workshops of Giovan Battista Giusti, 1556-c.1575', Nuncius. Annali di Storia della Scinza, x, 1, 1995, 151-72.
Sotheby's would like to thank Anthony Turner for his help in cataloguing this lot.
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