31. Instrument for the object lenses of G. Campani by E. Lelli
Ercole Lelli (Bologna 1702-1766)
length from 720 to 980 cm
The Bolognese Prospero Lambertini, who became Pope Benedict XIV, bought, in 1747, the whole of Giuseppe Campaniís Rome workshop from his children, who had continued the work there, and donated it to the Institute of Science. A large number of relics by Campani, including hundreds of metal moulds for all the different work phases of the various types of lenses and a dozen or so extraordinary lenses of different focal length signed by the author, can today be seen at the Physics Museum of the University of Bologna.
In occasion of the donation, Ercole Lelli built an instrument for mounting Campaniís long focal object lenses which was set up in the then courtyard to the south of the tower.
In the Commentaries of the Institute of Science (Tomo III, 1755, p. 19) there is the following quotation marking the Popeís gift and describing Lelliís instrument:
"... Benedictus XIV ad omnes, quaecumque se darent, occasiones intentus, hanc arripuit: elaboratissima vitra, et lentes Campanae pulcherrimas,...,in Institutum invehi jusserat, & dioptricae officinam costituerat. Hic illum non fugit de Specula; duasque ex objectivis Campanae lentibus longe pulcherrimas, & foci distantia insignes, ad eam deferri jussit, quibus astronomi in subtilioribus capessendis observationibus, uti opus esset, uterentur. Egregium sane munus; nam lentes tales numquam antea bononiensis Specula obtinuerat. Quo etiam machinam condidit commodissimam, expeditissimamque, qua telescopia quaeque vel longissima possint dirigi. Longiora tamen quam quae memoratis modo lentibus componuntur, locus non capit. Haec adhuc ad Astronomiam accesserunt."
Lelliís instrument is not specifically mentioned in the inventories, but a hand-written note by Eustachio Zanotti in the 1746 inventory (reviewed after 1757) mentions the wooden tubes for Campaniís 11-foot lens, a 22-foot one and an unspecified 30-foot lens, similar in length to the 33-foot lens by Campani that is still with us.
Identically made wooden square tubes matching the above-mentioned specifications, and a few relative accessories, have been traced and are listed as follows:
The first three tubes are reinforced by lagging at the eye-piece end to withstand introduction of the tubes. Into the last tube at the eye-piece end fits a pasteboard tube [Inv. MdS-191] with a 55 mm-diameter threaded ferrule for attaching two eye-pieces (lenses missing today), one with a focus of about 10 cm [Inv. MdS-192], the other [Inv. MdS-36], with the section bearing the field diaphragm missing, about 12 cm. Maximum magnification at maximum length would have been 196 times and, with the 33-foot object lens, 129.
- Mount for 10.5-foot object lens: not found. An object lens with a 12.5-foot focus (c. 480 cm) was however found bearing the words Joseph Bruni Bononiae f. A. 1767/p.12 [Inv. MdS-29]. In the 1746 inventory and the 1749 Nota two lenses by Bruni are mentioned: this one and another with a longer inscription, kept in the Physics Museum and dated 1771. Giuseppe Bruni, "mechanic" at the Institute of Science, was entrusted, on Ercole Lelliís death, with the equipment of Campani donated to the Institute. To prove his own competence and the efficiency of the instruments Bruni was expected to make an object lens every year with these instruments in the presence of the academic authorities.
- Mount for 22-foot object lens [Inv. MdS-2]: it consists of two square tubes 9 cm wide, 381 cm and 409 cm long respectively. A circular tube with external diameter of 0.8 cm protrudes from the shorter tube and can be inserted in one of the ends of the longer tube to reach a total length of 790 cm, equal to about 20.8 Bolognese feet. At the free end of the longer tube is fitted an object lens holder [Inv. MdS-63] designed to take Campaniís 22-foot lens. This is attached to the tube by a hook that fits a brass eye in the tube. The free end of the shorter tube is fitted with a pasteboard tube [Inv. MdS-133a], with a black wooden ferrule that acts as joint with the eye-piece [Inv. MdS-62], 18.6 cm long, that used to take a lens 3.2 cm in diameter and about 10 cm in focal length, as can be judged from the distance between the lens and the field diaphragm. This eye-piece magnified almost 80 times and the field of view was 26 arcminutes. 370 cm from the eye-piece, on the shorter tube, protrudes a brass eye which was used to hang the telescope.
- Mount for c. 30-foot object lens [Inv. MdS-1]: there are four square tubes that fit one inside the other. The tubes are 12.4, 10.7, 9.2 and 7.3 cm wide, respectively, and 250.5, 536, 536 and 536 cm long, for a total length of 18.6 m. If the introduction was at least 60 cm, as would seem to be the case judging by the marks on the second and fourth tube, then actual maximum length was reduced to 16.78 m, equal to 44 Bolognese feet. The length of 33 feet could be reached just by using the last three tubes.
None of the mounts of the bigger lenses have been found. The eye-piece tube has survived, comprising three colored cardboard tubes with black wooden ferrules 41, 42 and 30.5 cm long respectively and diameters of 5.5, 6 and 7 cm [Inv. MdS-133a,b,c].
Lelliís instrument most likely resembled the one illustrated in table VIII of Francesco Bianchiniís Hesperi et Phosphori nova Phaenomena sive observationes circa planetam Veneris, published in Rome in 1728, which was also made up of square tubes. Some pulleys and a counterweight have in fact been found which could have belonged to an instrument of that kind.
The instrumentís mount - using the tubes designed for Campaniís 22-foot object lens [file 29] - was restored in 1985, building a new stand and a leaf-spring to stop the telescope bending. The sighting and pantograph guide system was also rebuilt on a support stand of the period [Inv. MdS-61], using Christiaan Huygensí description of a similar instrument (table XXXI of first volume of Opera Varia published by J. Vander in 1724).
E. Baiada, A. Braccesi (1983), p. 120.
F. Bianchini (1728), tav. VIII.
M.L. Righini Bonelli (1981).