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A drum attachment to a travelling microscope for direct wavelength reading of spectral lines
SpcctrochlmicaActa, 1955.Vol. 7, p. 64, &?eetroGhemicuE
Pergamon Prew Ltd.. London
Note
A drum attachment to a tzavelling microscope for direct wavelength reading of spectral lines S. A. CLARKE British
Insulated
Callender’s
Cables Limited,
London
W.12
This instrument was developed to enable the ident~~tion of spectral lines, by their wavelength, to be carried out rel&ively simply. A helical expanded distance scale was traced on the drum, which was geared to the thread of the Baker 64 travelling microscope, by fixing a pen to the pointer on the microscope stage (Plate 1). This helix was calibrated for wavelength as follows: A record was made of the microscope scale-readings of known lines in reference spectra, pho~~aph~ in juxt&position. From these a table was constru~~d, by calcul&ion, of the scale readings corresponding to IOA intervals throughout the wavelength range. The nearest two lines, one each side of the wavelength for which the calculation was made, were used. This table was subdivided by simple proportion into smaller units. For example, a drum calibrated for plates exposed on the Bellingham and Stanley medium spectrogmph was divided into 0.5, l-0, 2.0, 50 A intervals in the ranges 2160-2700-3300-4200-6000 A respectively. This subdi~ded table WM transferred onto the drum, precautions being taken that movement was in one direction only to eliminate the effect of biacklash. A scale, fixed rigidly between the curved end-supports, was used as the marking line, and the portion of the helix marked was indicated by the pointer. The reading line, which was supported by a thin curved perspex sheet fixed on the endsupports as close as possible to the drum surface, was a spring loaded wire attached to runners in the end-supports. The maximum movement of the reading wire round the drum ~ireumference st each end was 75 cm, which was equivalent to 3 mm along the plate. This adjustment accommodated the observed variation in the distance between the same spectral lines on different plates. In use, after the reading wire is set parallel to the drum a.xis, the drum is rotated until the wire indicates the wavelength of a known line in the low wavelength region, The plate is moved until the line coincides with the hair line of the microscope eyepiece. The drum is rotated until a known line in the high wavelength region coincides with the hair line. The reading wire is then adjusted, at this end of the drum, so that the correct wavelength is indicated. This adjustment will have altered slightly the position of the reading wire at the low wavelength end, so, t&ing precautions against backlash, the hair line is set again on the first line and the reading wire adjusted at that end so that the correct wavelength is indicated. By repeating the process of adjusting the reading wire at ttltenmte ends of the drum, an optimum position is established when the correct wrtvelength is indicated with the hair line set on either of the known lines. The wavelength of other lines can now be read directly from the drum. The average difference between indicated and true wavelength of single readings on many spectral lines was 0.25, O-55, 676, 0.64, O-60, 090~ in the wavelength ranges: 2160-2400-2700-3000-3300-36004700 A respectively, for a drum calibrated for the medium spectrograph. A similar drum calibrated for the 2700-4450 A range for the Hilger large quartz spectro~&ph gave 0.22A as the average difference between indicated and true wavelength of single resdings on many lines. It was noted that errors were unidirectional and their magnitude changed progressively. It wss found possible to make “ad hoc” allowances for these small errors by reference to lines identified previously. The author wishes to thank the directors of British Insulated Callender’s Cables Ltd. for their permission to publish this work. 64
PLATE A drum attachment
to a travelling microscope
1
for direct wavelength
reading of spectral lines.
Pergamon Prew Ltd.. London
Note
A drum attachment to a tzavelling microscope for direct wavelength reading of spectral lines S. A. CLARKE British
Insulated
Callender’s
Cables Limited,
London
W.12
This instrument was developed to enable the ident~~tion of spectral lines, by their wavelength, to be carried out rel&ively simply. A helical expanded distance scale was traced on the drum, which was geared to the thread of the Baker 64 travelling microscope, by fixing a pen to the pointer on the microscope stage (Plate 1). This helix was calibrated for wavelength as follows: A record was made of the microscope scale-readings of known lines in reference spectra, pho~~aph~ in juxt&position. From these a table was constru~~d, by calcul&ion, of the scale readings corresponding to IOA intervals throughout the wavelength range. The nearest two lines, one each side of the wavelength for which the calculation was made, were used. This table was subdivided by simple proportion into smaller units. For example, a drum calibrated for plates exposed on the Bellingham and Stanley medium spectrogmph was divided into 0.5, l-0, 2.0, 50 A intervals in the ranges 2160-2700-3300-4200-6000 A respectively. This subdi~ded table WM transferred onto the drum, precautions being taken that movement was in one direction only to eliminate the effect of biacklash. A scale, fixed rigidly between the curved end-supports, was used as the marking line, and the portion of the helix marked was indicated by the pointer. The reading line, which was supported by a thin curved perspex sheet fixed on the endsupports as close as possible to the drum surface, was a spring loaded wire attached to runners in the end-supports. The maximum movement of the reading wire round the drum ~ireumference st each end was 75 cm, which was equivalent to 3 mm along the plate. This adjustment accommodated the observed variation in the distance between the same spectral lines on different plates. In use, after the reading wire is set parallel to the drum a.xis, the drum is rotated until the wire indicates the wavelength of a known line in the low wavelength region, The plate is moved until the line coincides with the hair line of the microscope eyepiece. The drum is rotated until a known line in the high wavelength region coincides with the hair line. The reading wire is then adjusted, at this end of the drum, so that the correct wavelength is indicated. This adjustment will have altered slightly the position of the reading wire at the low wavelength end, so, t&ing precautions against backlash, the hair line is set again on the first line and the reading wire adjusted at that end so that the correct wavelength is indicated. By repeating the process of adjusting the reading wire at ttltenmte ends of the drum, an optimum position is established when the correct wrtvelength is indicated with the hair line set on either of the known lines. The wavelength of other lines can now be read directly from the drum. The average difference between indicated and true wavelength of single readings on many spectral lines was 0.25, O-55, 676, 0.64, O-60, 090~ in the wavelength ranges: 2160-2400-2700-3000-3300-36004700 A respectively, for a drum calibrated for the medium spectrograph. A similar drum calibrated for the 2700-4450 A range for the Hilger large quartz spectro~&ph gave 0.22A as the average difference between indicated and true wavelength of single resdings on many lines. It was noted that errors were unidirectional and their magnitude changed progressively. It wss found possible to make “ad hoc” allowances for these small errors by reference to lines identified previously. The author wishes to thank the directors of British Insulated Callender’s Cables Ltd. for their permission to publish this work. 64
PLATE A drum attachment
to a travelling microscope
1
for direct wavelength
reading of spectral lines.