Acromatic refractor

Robert-Aglaé Cauchoix, Parigi, 1825
Glass, metal
Diameter Ø 16,9 cm
Focal length f=238 cm
Museum of INAF-Astronomical Observatory of Rome, Monte Porzio Catone (Rome)

The telescope, acquired by the astronomical Observatory of the Roman College o in the year 1825, was initially installed on an altazimuth mount (Figure 1).
On August 5, 1835 with Cauchoix refractor the comet of Halley was “rediscovered” by Fr. Etienne Dumouchel, thanks above all to the work done by Padre De Vico who, from the determinations of the orbit of the comet derived from the previous apparitions, calculated the probable position and put it in a chart of the sky. It is due to this work if the famous comet could be observed from the Roman college long before the other observatories.
In the renovation work of the Astronomical Observatory of the Roman College, Angelo Secchi placed the telescope on an equatorial mount and used it for photographic and visual observations of the solar photosphere; In addition, with the help of the Objective Prism he made numerous observations on which his famous spectral classification of stars was based.
For its exceptional optical quality, the objective was installed in 1886 on a new equatorial mount, realized by Giuseppe Cavignato (skillful mechanic of the Observatory of Padua from 1877 to 1909) by will of Pietro Tacchini, successor of Secchi in Direction of the Observatory of the Roman College. The telescope remained in service until the years ‘ 80 of the twentieth century at the Astronomical Observatory of Rome.
In 1913, with this same instrument, coupled with the objective prism, Giorgio Abetti photographed the spectra of several stars analysed by Secchi for his classification and studied the optical characteristics of the instrumentation he used.
Recently the lens has been relocated to the original tube of the 1825, shown here.

Aldo Altamore, Università degli Studi “Roma Tre”
Marco Faccini, INAF-Osservatorio Astronomico di Roma