Usage/History: The oldest optical method for chemical
analysis, Bunsen and Kirchhoff introduced spectroscopy as a laboratory
method in 1860. The basic features of the spectroscope (or spectrometer)
include a slit and collimator to produce a parallel beam of light
which then falls on the dispersive element (a prism or grating).
The resulting spectrum is then observed through a telescope.
Spectrometers are particularly valued in two types of studies:
1) The identitfication and quantification of elements by the
observation of line spectra (emission or absorption), 2) The
identification and quantification of substances by the observation
of absorption bands.
In this spectrometer the prism table, the collimator, and
the telescope positions may be determined relative to a graduated
circle. This example is Gaertner's student instrument. It could
be used for the determination and analysis of spectra using either
a prism or grating. It could also be used in the measurement
of angles between prism faces, the determination of angles of
refraction and reflection etc. In another common type of instrument,
the Bunsen
Spectroscope, there is no graduated circle, instead measurements
are made relative to a projected scale.
Some contemporary/early descriptions of the spectroscope
and its use are provided below:
"The
Spectrometer" in Minor. Physical Measurements:
... Sound and Light (1917)
Description: Gaertner small model spectroscope. The
graduated aluminum circle is 125mm dia, with divisions every
30' and two verniers reading to 1'. A black japanned brass plate
protects the graduated circle, having oval cutouts at 180°
for reading the verniers. The instrument is stamped on the plate
in white filled letters: WM. GAERTNER & CO / CHICAGO / 323.
The circle with the attached telescope and the vernier plate
move independently, and are both equipped with clamp and tangent
screws. The aluminum prism plate is 80mm dia, and is fitted with
leveling screws and a clamp for the prism (missing). The telescope
and collimator are each held in a cast iron double cradle by
five adjusting screws: two near the objective provide a pivot,
while the remaining three provide horizontal and vertical angular
adjustment. The entire instrument sits on a substantial cat iron
tripod. All adjusting screws are of polished nickel plated brass
with checkered knurling. The telescope and collimator each have
25mm objectives and 160mm? focal length. The slit has nickel
silver jaws, adjusted by a screw to the side (replacement). The
telescope focuses by means of a knurled ring. The eyepiece is
equipped with a beam splitter accessed through a hole to the
right side for superimposing scales etc. on the spectral image.
An oval brass tag, attached with brass pins to the opposite right
of the collimator, is stamped: HUMBOLDT S-T-C / 2103.
Bibliolgraphy:
Bennet, J. A. The Celebrated Phaenomena of Colours: the
early history of the spectroscope. Whipple Museum of the
History of Science, Cambridge (1984).
Brand, John C. D. Lines of Light: The Sources of Dispersive
Spectroscopy, 1800-1930. Gordon and Breach Publishers (1995)
Minor, Ralph S., Physical Measurements, A Laboratory Manual
in General Physics for Colleges: Part 2, Magnetism and Electricity,
Sound and Light 3rd ed, Associated Student's Store, Berkeley
(1956) pp. 118-121, 122-124, 158-159.