Index of spectra / by W. Marshall Watts ; with a preface by H.E. Roscoe.

Date:
1872
Catalogue details

Licence: Public Domain Mark

Credit: Index of spectra / by W. Marshall Watts ; with a preface by H.E. Roscoe. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    each of two known lines between which it falls can thus be determined with great precision. Instead of employing the method of graphical interpolation, the wave-length may be calculated by means of the following interpolation formula (W. Gibbs, Silliman's Journal, July, 1870 ; Phil. Mag. [4] * xl., 177) K 'V where and »i are the readings on the scale of the specftro- scope of the two known lines, X3 and Xj their wave-lengths, «2 the reading of the line to be measured, and its wave- length. The following example will render the use of the formula clear:—One of the brightest lines in the spe(5trum of the Bessemer flame falls between two bright lines pro- duced by cadmium. Reference to the table shows that these lines have wave-lengths 5378 and 5337 respectively. When the cross wires of the telescope were made to coin- cide with the lines, the micrometer-screw of the instrument gave the readings 14*38 and i5'27, while, when the wires were brought on the Bessemer line, the reading was 14*81. Putting, then, «3 = 15*27, X3 = 5327, = 14*38, Xj = 5378, and «2 = 14*81, we find for X2 the value 5358. If the line to be determined lies near to the two reference lines, but not between them, the interpolation formula given above must be replaced by one of the two following extra- polation formulae. M3 — n^—n^ _n2 — ni n^—Hj _ «3—«2 * In the formulas i and 3, on p. 178, there is a misprint of -f for - in th« denominator.