. Carnegie Institution of Washington publication. harp quiet fringes are obtained withsunlight (white), in which the cross-hatched interference pattern is nearly•linear at the line of symmetry of the reversed spectra. The fringes climbvery decisively up and down this line with the motion of the micrometer,reduced as suggested. The electric arc and a Nernst filament are equallyavailable as a source of light. Finally, by suitably rotating the grating G,figure 2, on the axis e, by aid of the set of screws d, fringes whose distanceapart is over one-third of the width of the telescope field may be
. Carnegie Institution of Washington publication. harp quiet fringes are obtained withsunlight (white), in which the cross-hatched interference pattern is nearly•linear at the line of symmetry of the reversed spectra. The fringes climbvery decisively up and down this line with the motion of the micrometer,reduced as suggested. The electric arc and a Nernst filament are equallyavailable as a source of light. Finally, by suitably rotating the grating G,figure 2, on the axis e, by aid of the set of screws d, fringes whose distanceapart is over one-third of the width of the telescope field may be obtainedquite sharply. As this distance represents but 30X icr45 cm., there is no diffi-culty of realizing lo6 cm. in case of these long fringes. 3. Measurements. First= and second-order spectra.—The steadiness of thefringes, even in an agitated location, induced me to make a few measurementsior orientation. Accordingly, the Fraunhofer micrometer, reading to icr4 cm.,was provided at its screw-head with a light wooden wheel w, figure 4, about.
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