138
8.2 Stellar Spectroscopes
Secchi’s stellar spectroscopes share many design features common to their solar
counterparts, with a similar layout and interchangeable components. While solar
spectroscopes owe their origins to progenitors used in the chemical laboratory, their
stellar counterparts were modified to accommodate the much dimmer starlight collected at the telescope.
8.2.1 Direct-Vision Spectroscope
From Secchi’s own writing in Le stelle (Secchi 1877), we learn how, with
P. Jules C. Janssen (1824–1907) in 1862 (Barthalot 2007: 588–9), he obtained his
first stellar observation (α Orionis), using a direct-vision spectroscope:
The arrival in Rome of the news of this spectroscope was almost contemporaneous with that
of Donati’s own account of it. Immediately the idea was conceived of making use of it on
the stars by applying it to our great refractor, in the hope of having better results than those
of Donati, given the high quality of our Merz objective. The spectroscope was ordered
immediately, but it did not arrive until December in the same year. Meanwhile, Mr. Janssen
came to Rome to study the solar spectrum, and as he had one of these small spectroscopes
I asked him to apply it to our refractor for temporary use until mine arrived. He agreed and
together we made the first observations, which were reported at the Paris Academy. The
study of solar and chemical spectroscopy was already well progressed, not only looking for
spectral lines but also looking to understand their nature, and by early evening we were able
to ascertain the existence of sodium and other metals in the α star of Orion. (Secchi 1877a:
39; Janssen 1863: 71)
1
The type of instrument used is described and illustrated in the same work (see
Fig. 8.1). It was a form of direct-vision spectroscope devised by the optician Dr.
J.G. Hofmann in Paris, consisting of five prisms (three crown and two flint) cemented
together. It produced a large dispersion of the light beam, but without deviation of
the light-path, in contrast to a simple prism spectroscope that bends it. The idea was
first devised by Giovanni Battista Amici (1786–1863) and then applied by Giovan
Battista Donati (1826–1873) to the spectroscope (Pietrolungo 2007; Baum 2007a).
1 L’arrivo in Roma della notizia di questo spettroscopio fu quasi contemporaneo con quello della
memoria del Donati. Immediatamente concepì l’idea di farne un uso per le stelle applicandolo al
nostro grande rifrattore, nella speranza di aver migliori risultati di quelli del Donati, attesa la gran
perfezione del nostro obbiettivo di Merz. Lo strumento fu ordinato immediatamente, ma esso non
giunse che al decembre dello stesso anno. Intanto essendosi recato a Roma il signor Janssen per
istudiare lo spettro solare, e avendo seco uno di questi piccoli strumenti, gli chiesi di applicarlo al
nostro Refrattore per servircene provvisoriamente finchè arrivasse il mio. Esso condiscese e furono
insieme con lui fatte le prime ricerche delle quali fu dato notizia all’Accademia di Parigi. Lo studio
della spettroscopia solare e chimica era già tanto progredito che non solo cercammo l’esistenza
delle linee spettrali, ma anche la loro natura, e fin dalle prime sere potemmo accertare nella stella
α di Orione l’esistenza della riga del sodio ed altri metalli.
K. L. Johnson
8.2 Stellar Spectroscopes
Secchi’s stellar spectroscopes share many design features common to their solar
counterparts, with a similar layout and interchangeable components. While solar
spectroscopes owe their origins to progenitors used in the chemical laboratory, their
stellar counterparts were modified to accommodate the much dimmer starlight collected at the telescope.
8.2.1 Direct-Vision Spectroscope
From Secchi’s own writing in Le stelle (Secchi 1877), we learn how, with
P. Jules C. Janssen (1824–1907) in 1862 (Barthalot 2007: 588–9), he obtained his
first stellar observation (α Orionis), using a direct-vision spectroscope:
The arrival in Rome of the news of this spectroscope was almost contemporaneous with that
of Donati’s own account of it. Immediately the idea was conceived of making use of it on
the stars by applying it to our great refractor, in the hope of having better results than those
of Donati, given the high quality of our Merz objective. The spectroscope was ordered
immediately, but it did not arrive until December in the same year. Meanwhile, Mr. Janssen
came to Rome to study the solar spectrum, and as he had one of these small spectroscopes
I asked him to apply it to our refractor for temporary use until mine arrived. He agreed and
together we made the first observations, which were reported at the Paris Academy. The
study of solar and chemical spectroscopy was already well progressed, not only looking for
spectral lines but also looking to understand their nature, and by early evening we were able
to ascertain the existence of sodium and other metals in the α star of Orion. (Secchi 1877a:
39; Janssen 1863: 71)
1
The type of instrument used is described and illustrated in the same work (see
Fig. 8.1). It was a form of direct-vision spectroscope devised by the optician Dr.
J.G. Hofmann in Paris, consisting of five prisms (three crown and two flint) cemented
together. It produced a large dispersion of the light beam, but without deviation of
the light-path, in contrast to a simple prism spectroscope that bends it. The idea was
first devised by Giovanni Battista Amici (1786–1863) and then applied by Giovan
Battista Donati (1826–1873) to the spectroscope (Pietrolungo 2007; Baum 2007a).
1 L’arrivo in Roma della notizia di questo spettroscopio fu quasi contemporaneo con quello della
memoria del Donati. Immediatamente concepì l’idea di farne un uso per le stelle applicandolo al
nostro grande rifrattore, nella speranza di aver migliori risultati di quelli del Donati, attesa la gran
perfezione del nostro obbiettivo di Merz. Lo strumento fu ordinato immediatamente, ma esso non
giunse che al decembre dello stesso anno. Intanto essendosi recato a Roma il signor Janssen per
istudiare lo spettro solare, e avendo seco uno di questi piccoli strumenti, gli chiesi di applicarlo al
nostro Refrattore per servircene provvisoriamente finchè arrivasse il mio. Esso condiscese e furono
insieme con lui fatte le prime ricerche delle quali fu dato notizia all’Accademia di Parigi. Lo studio
della spettroscopia solare e chimica era già tanto progredito che non solo cercammo l’esistenza
delle linee spettrali, ma anche la loro natura, e fin dalle prime sere potemmo accertare nella stella
α di Orione l’esistenza della riga del sodio ed altri metalli.
K. L. Johnson