12. Movable quadrant by D. Lusverg
Rome, 1703
Domenico Lusverg (1669 - 1744)
brass and iron
2 fixed telescopes
radius 117 cm
[Inv. MdS-117]

Despite the failure of the first instrument [file 11], Manfrediís confidence in Domenico Lusverg was in no way shaken and this second instrument was commissioned from him. Left this time to his own devices, the craftsman came up with a real masterpiece, whose scale was engraved with such precision and sharpness as to be second to none and replaced, in practice, the first quadrant. In line with Manfrediís request, the limb is slightly longer than 90į, so as to be able to use the verification method for the instrument employed by the French astronomers, consisting of "turning it upside down".
The features engraved on the limb were accurate to one hundredth of a millimetre and with this instrument Manfredi began using the method of corresponding elevations to compute the transit time of the stars across the meridian, achieving an accuracy that made errors greater than two arcseconds rare; the quadrant could therefore be used to check the operative regularity of clocks and the accuracy of the mural semicircle (see Part I, par. 11).
It was described in the 1712 Instrumentum donationis as follows:
"Quadrans alter eadem forma, atque opificio eodem, à Lusvergo etiam fabrefactus, omnia priori similis, eodemque instructo, sed ferrea eius contignatio perpendiculariter quadrantis plano insistit. Limbus etiam est illi paulo latior, & exquisitiori divisione incisus."
It was modified in 1728 (Reg. Specola Ist. Scienze, Vol.II, dated 23 March 1728, Arch. Dept. Astron. Bo.), when Manfredi added a second telescope perpendicular to the original and reduced the number of supports from 4 to 3, to make it less cumbersome and enable observations to be made through the opening that ran across the roof of the Meridian Room.
Like the previous quadrant [file 11], this instrument is not signed and the central brass escutcheon bears the same engraving: the Marsili coat-of-arms crowned with the words Aloysius Ferdinandus Comes Marsigli.
From at least 1746 the movable telescope went missing, and from 1843, when the pendulum still existed, the swivel junction or third axis, that allowed the instrument to be used as an astronomical sextant, went the same way. The objective lens of one of the fixed telescopes is an original.

The instrument was restored by Giovanni Morigi (Bologna) in 1979.

E. Baiada, A. Braccesi (1983) p. 86.
M. Daumas (1953), p.91.
E. Miotto, G. Tagliaferri, P. Tucci (1990) p.95 ff.
G. Tabarroni (1954) p.43.
P. Todesco (1995)..