YPML.000025

SPENCER

Instrument

American Optics

TABLE NO. I
FRAUNHOFER LINES

<table><thead><tr><th>Symbol</th><th>Element</th><th>Wave-length, mµ</th><th>Symbol</th><th>Element</th><th>Wave-length, mµ</th></tr></thead><tbody><tr><td>A</td><td>O</td><td>762.1</td><td>b<sub>4</sub></td><td>Fe</td><td>516.7</td></tr><tr><td>B</td><td>O</td><td>759.4</td><td></td><td>Mg</td><td></td></tr><tr><td>C</td><td>H</td><td>687.0</td><td>F</td><td>H</td><td>486.1</td></tr><tr><td>D<sub>1</sub></td><td>Na</td><td>565.3</td><td>G'</td><td>H</td><td>434.0</td></tr><tr><td>D<sub>2</sub></td><td>Na</td><td>589.6</td><td></td><td>Fe</td><td></td></tr><tr><td>E<sub>2</sub></td><td>Fe</td><td>527.0</td><td>G</td><td>Ca</td><td>430.8</td></tr><tr><td>h<sub>1</sub></td><td>Mg</td><td>518.4</td><td>g</td><td>Ca</td><td>422.7</td></tr><tr><td>h<sub>2</sub></td><td>Mg</td><td>517.3</td><td>h</td><td>H</td><td>410.2</td></tr><tr><td></td><td></td><td></td><td>H</td><td>Ca</td><td>396.8</td></tr></tbody></table>

It was soon discovered that these absorption lines appear at wave-lengths corresponding to emission lines in the spectra of terrestrial elements. By identifying these radiations in the laboratory the constitution of the sun has been studied. This relationship

Fig. 1. The Spencer Spectrometer. A—Slit; B—Collimator Objective; C—Dispersing Prism; D—Telescope Objective; E—Position of Cross Hairs; F—Prism Table Clamping Screw; J—Prism Table Clamping and Tangent Screws; K—Telescope Arm Clamping and Tangent Screws; L—Eyepiece Ring; M—Telescope Focusing Ring; N—Divided Circle Dust Cover; O—Prism Table Leveling Screws; P—Collimator and Telescope Leveling Screws; Q—Telescope Bearing Front Screw; R—Telescope Bearing Side Screws.

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between the constituents of the sun and of terrestrial sources was first investigated by Bunsen and Kirchhoff. These scientists studied the spectra of many substances which not only established the presence of many earth-known elements in the sun, but also formed a foundation for the entire science of spectroscopic analysis.

In the early days spectroscopes had two types of scales for recording the position of the spectral lines. In one type of instrument, represented by the Spencer spectrometer as its modern counterpart, see fig. 1, the position of the prism table and of the telescope can be determined by reference to a very accurately divided circular scale which is read with verniers. Instruments of this type have been developed to their highest precision for the purpose of making accurate measurements of the refractive index of transparent materials in prism form at various wave-lengths. In the other type of instrument, shown in the frontispiece and exemplified by the Spencer spectrometer used with the Bunsen spectroscope attachment, see fig. 2, an arbitrary scale suitably illuminated is reflected from the back surface of the prism and appears in the telescope superimposed on the spectrum being observed. The pioneers in spectroscopy were familiar with both these types of instruments and for wave-length studies and for the identification of chemical elements the second type was commonly em-

Fig. 2: The Spencer Bunsen Spectroscope Attachment, G—Semi-transparent Diagonal Mirror; S—Bunsen Attachment Collimator; T—Bunsen Attachment Prism Table Cover; U—Wave-length Scale.

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