38. 3-foot parallactic telescope with achromatic object lens by Dollond
John Dollond Jr. (London ?-1804)
Peter Dollond (London 1730-1821)
brass, triangular three-footed walnut table with marble top
length of tube 112 cm, diameter 9 cm
"Parallactic device by Dollond adapted to the Bologna latitude, with 3-foot telescope and achromatic object lens of 2 and Ĺ-inch aperture; able to perform small movements in both Right Ascension and Declination by means of two graduated semicircles on which slide verniers that provide the arcminutes. Attached to the telescope is a small guide telescope whose optical axis can be made parallel to the axis of the former. By means of three screws fixed to the end of the mahogany frame, on which is mounted the instrument, this latter can be levelled as indicated by two air-bubble levels attached at right angles to the selfsame frame...A triangular walnut Table with three feet joined together by cross-beams, that runs on metal runners, with three iron screws to make it stable, which serves as support for Dollondís Parallactic instrument.
Part of the consignment bought in 1787 [files 37-41] this instrument, as the 1843 inventory reminds us, was equipped with:
The telescope, fitted with achromatic and aplanatic 3-lens objective, the last breakthrough for the period, from the Dollond workshop [file 37], was used for almost two centuries, and remained operational as auxiliary telescope on the 60 cm telescope in Loiano until as late as 1982.
- "No.3 astronomical eye-pieces of different magnification, each of which is provided with colored glass for observing the Sun.
- An astronomical eye-piece with rhomboidal micrometer.
- Another similar, in half of which there are metal bars.
- A circular micrometer by Amici with astronomical eye-piece [Inv. MdS-43] [file 42].
- Two eye-piece holders which can take the eye-pieces of the transit Telescope.
- A divided object glass Micrometer, or Heliometer... [Inv. MdS-41] [file 41].
- A counterweight to be applied to the eye-piece end of the Telescope to counterbalance the Heliometer.
- A piece of tube to add to the eye-piece holder when the Heliometer is applied.
- Reflector to be placed at the object lens end [Inv. MdS-44].
- Protective cover for object lens.
- Triangular marble table [Inv. MdS-159] inlaid with pieces of brass, with three-leg walnut stand where there are three screws that hold metal runners that make it movable; This serves as support for Dollondís Parallactic Telescope."
Originally the telescope was equipped with three astronomical eye-pieces and one terrestrial. Since the telescope was used in Loiano, where the original tube was tampered with and replaced by a new one, it has been possible to recuperate only two stumps, without the original object lens attachment, of the eye-piece holder and relative threaded rod focusing mechanism. These parts have therefore been restored as too has the auxiliary telescope (S. Ciattaglia 1982).
The absence of the original eye-piece holder has made it difficult to identify the above-mentioned eye-pieces, all the more so since not even the eye-piece holder of the transit telescope of Reichenbach, Utzschneider und Liebherr [file 20] has been found which would have enabled identification of the two afore-mentioned adaptors, if still existent. The series of eye-pieces presently attributed to the instrument, including the one mounted on the telescope [Inv. MdS-67], are therefore somewhat conjectural.
An attachment for a screen for observing the Sun in projection, not mentioned in the inventory description, has also been found [Inv. MdS-45]. This accessory was also restored in 1982. Of the various handles for moving the device, only the one for declination movements has been found, broken at its join; it was restored in 1982 and has since been used as model to remake the other handle for right ascension movements.
As recorded in the original bill of sale of the Rubini brothers, dated 5 October 1788, to the Administrators of the Institute, discovered in the Archives of the Department of Astronomy (busta XXVIII), the instrument cost £63, or 1520 Bolognese lire.
E. Baiada, A. Braccesi (1983), p. 122.
M. Daumas (1953), p. 315.
G. LíE. Turner (1981)