33. Marinoni position micrometer by J. Scherer
Vienna, 1732
Jacob Scherer (fl.1732)
length 24.5 cm
[Inv. MdS-37]

"Gift of the then Sig. Dott. Eustachio Manfredi / A moving-wire micrometer with its screws, and its indices, all enclosed in a Case, and brass tube. A two-lens telescope belongs to this micrometer with tin tube and brass ends, about six foot long" (1746 inventory).
The telescope was not found and could no longer be identified in the inventory of 1843. The micrometer, however, has survived - complete with wires and glass eye-piece - identical to the one illustrated in table 4, section 6 of Marinoniís book De Astronomica Specula Domestica (Vienna, Kaliwoda, 1745).
It is almost certainly the only remaining example of the micrometers designed by Giovanni Giacomo Marinoni from Udine (1676-1755). Matematico Cesareo and hence director of the Military Academy in Vienna, he set up an astronomical observatory in his Viennese house, described in the above-cited work. The various instruments are described in detail along with their actual positions in the building, so that the reader has an exact idea of how an XVIIIth-century specola was arranged.
Marinoni sent Eustachio Manfredi a gift of his position micrometer invention, with metal box and eye-piece lenses, that he had purposely made by J. Scherer in 1732, as can be seen from the inscription on the sides of the instrument where we find the screws, both on the movable and fixed parts.
Eustachio Manfredio / Celeb. Astronomo Ital.o / Microm. hoc rec. invent. / Ad usum Bonon. Academ.ae / J.Jac. Marinonius Nob. Utin. / Amico Optimo d.d. // Jac: Scherer f. / Viennae Austr. / in aedib. D. d. Marinoni / an. 1732.

The instrument came with a hand-written description and instructions how to use it. On the last page of volume IV of the Records of the Specola di Bologna, dated 4 May 1734, there is a calibration table for the micrometer written by the same Manfredi that gives the relation between a turn of the micrometric screw and the angle measurement, essential for use of the instrument.

The first micrometer was built and used by the Englishman William Gascoigne (c.1620-1644) in 1639 (Repsold, op. cit., p.17), but his invention was only revealed by Richard Townley after the publication in December 1666 of a letter by Adrien Auzout (1622-1691) on the technique for measuring the diameter of the planets (Repsold, op. cit., p.42). The micrometer was then developed by John Bird (1709-1776) and for the first time in 1745, at the behest of Bradley, was applied to a mural quadrant by Graham in Greenwich. For an exhaustive account of the development of the micrometer see the cited work by Randall C. Brooks of 1991.

E. Baiada, A. Braccesi (1983), p. 117.
J.A. Bennett (1987), p. 63.
G. Boffito (1929), p. 129, tab. 81.
R.C. Brooks (1991).
A. Chapman (1990), p. 40.
M. Daumas (1953), p. 69.
E. Miotto, G. Tagliaferri, P. Tucci (1989), p. 97.
J.A. Repsold (1908), pp. 62-64, Figs. 80a and b, 81, 82.