. Carnegie Institution of Washington publication. DESCRIPTION OF APPARATUS AND METHODS. I9 from the mirror also forms an image of the sHt upon the sHt. Since the slit lies in the axis of the collimating mirror, the prism and its mirror are truly vertical and parallel only when they reflect the image of the slit back upon the slit. The angle m (fig. 2) between the mirror and the prism face was deter- mined by reflecting the beam from the prism face back upon its path, thus forming an image upon the slit (or, better still, upon a fine line on a piece of paper just above it) and then noting the a
. Carnegie Institution of Washington publication. DESCRIPTION OF APPARATUS AND METHODS. I9 from the mirror also forms an image of the sHt upon the sHt. Since the slit lies in the axis of the collimating mirror, the prism and its mirror are truly vertical and parallel only when they reflect the image of the slit back upon the slit. The angle m (fig. 2) between the mirror and the prism face was deter- mined by reflecting the beam from the prism face back upon its path, thus forming an image upon the slit (or, better still, upon a fine line on a piece of paper just above it) and then noting the angular rotation of the prism table necessary to reflect the slit image upon the mirror back. Fig. 2. upon the slit. By this method the variation in the settings was only from 5" to 6" from the mean. To determine the " zero setting " of the instrument it is necessary to determine the angle p (fig. 2), at which the incident rays from the colli- mating mirror must fall upon the prism mirror, in order that the rays reflected from it will enter the prism and emerge from it at minimum deviation. If we know this angle for the sodium lines, after fixing the spectrometer arms and rotating the prism table, then all the succeeding wave-lengths will pass through at minimum Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Carnegie Institution of Washington. Washington, Carnegie Institution of Washington
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