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G. C. Dunlap and J. G. Trump, Rev. Sci. Inst. 8, 37 (1937).
A test for the normality of the spectrum produced by the grating-lens combination was made on three lines of the molecular spectrum of hydrogen covering a range of 250A approximately centered about the Hβ line, namely 4719.01A, 4849.32A and 4973.26A. The following figures were obtained for the quantity A/mm:A/mmInterval 4719.01–4849.32A PlateA,measuredupwardonscrew10.870 “““downward““10.875 PlateB,“upward““10.876 “““downward““10.877Mean10.874Interval 4849.32–4973.26A PlateA,measuredupwardonscrew10.877 “““downward““10.874 PlateB,“upward““10.872 “““downward““10.870Mean10.873A hyperbolic deviation from linearity, such as would produce an apparent shift of the center of gravity of the magnitude in question in this investigation would mean a difference of 0.5 A/mm in the quantity for the two wave-length ranges measured.
With this arrangement the real image which the mirror forms of the discharge is not coincident with the discharge but falls on the other side of the spectrograph slit. It was not believed that this lack of optical symmetry was important when weighed against the accuracy of alignment rendered possible. However, to test this point a tube was constructed furnished with a concave mirror which, by the aid of cross hairs in the discharge path, could be adjusted to image the discharge upon itself. This tube while more difficult to align accurately, gave identical results, as did also a tube with a plane mirror, so that any suspicion that the phenomena observed could be ascribed to optical dissymmetry is untenable.
Canal-ray spectra. (a) Undisplaced and displaced lines in tube of original type. (b) Undisplaced and displaced lines in tube of Dempster design.
(a) Molecular spectrum of hydrogen in the neighborhood of H
Chief molecular spectrum lines of hydrogen in the neighborhood of H
Computed and observed second-order shifts, plotted against voltage.
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