Direct Vision Spectroscope

Merz, Munich (Germany), 1863
Brass, glass
Length cm 40
Museum of INAF-Rome Astronomical Observatory, Monte Porzio Catone (Rome)

The instrument shown here is similar to the one described by Secchi in 1867 in its first memoir on stellar spectra and in the Le Soleil treatise. It is a direct-vision spectroscope with five prisms, and is the result of a series of tests carried out by Secchi to improve the results of the spectral observation of the stars. For this reason, Merz himself, the main partner of Secchi in the making of spectroscopic instruments, wanted to advertise it as “Secchi stellar spectroscope”. Among the various adjustments, Secchi replaced the micrometer spider wires – difficult to observe in the case of weak stars – with two metallic tips, which partially overlapped the spectral line to be measured.
This is but one example of the practice adopted by Secchi to modify and construct the instruments, adapting them to his research needs, interacting with the mackers or asking the help of mechanical experts – a practice that applied in the various disciplines he dealt with, from meteorology, to geodesia, etc.
some Instruments, which he made or improved in the use, even in other scientific disciplines, still dear carry his name (see Secchi disc).

Ileana Chinnici, INAF-Osservatorio Astronomico di Palermo

A. Secchi, “Sugli spettri prismatici delle stelle fisse”, Atti dell’Accademia Italiana delle Scienze detta dei XL (1867), p. 72; A. Secchi, Le Soleil, vol. I (1875), p. 231; A. Secchi, Le Soleil, vol. II (1877), p. 446; I. Chinnici, « The maker and the scientist : the Merz-Secchi connection » , Merz Telescopes (I. Chinnici ed.), Springer 2017, 39-68.