The London, Edinburgh and Dublin philosophical magazine and journal of science . cribed admits of the highest precision, and may be applied tothe exact measurement of the angle of minimum deviation ofthe spectrum-rays. It has been thus possible to apply the greatdispersive power of the large Cambridge spectroscope in deter-mining the relative position of the various spectrum-lines, andto secure all the accuracy of which angular measurements arecapable. The value of such measurements is obvious, and, withthe hope that this method will prove to be an assistance to inves-tigators, we propose to g
The London, Edinburgh and Dublin philosophical magazine and journal of science . cribed admits of the highest precision, and may be applied tothe exact measurement of the angle of minimum deviation ofthe spectrum-rays. It has been thus possible to apply the greatdispersive power of the large Cambridge spectroscope in deter-mining the relative position of the various spectrum-lines, andto secure all the accuracy of which angular measurements arecapable. The value of such measurements is obvious, and, withthe hope that this method will prove to be an assistance to inves-tigators, we propose to give in this paper a description of ourinstrument and of the manner of using it. * Riess, op. cit. vol. ii. pp. 80 & 130. t Notice sur Vappareil de Ruhmkorff, 4th edit. p. 248 (1859). Re-cherches sur la non-homogeneite de IVtinceUe dinduction, p. 89 (1860).t From Sillimans American Journal for November 18()5. Mr. J. P. Cooke on a Spect?*oscope. Ill The general construction of the instrument is shown infig. 1. The two telescopes are constructed in the usual way. The Fie. telescope A, which we shall call the collimator,, has an adjust-able slit placed exactly at the focus of the object-glass. Thesmall tube which carries the slit slides into the body of the tele-scope, but a rack-and-pinion motion would be preferable, sothat when the focus is changed the slit will necessarily remainvertical. The rays of light diverging from the slit and renderedparallel by the object-glass of the collimator next pass througha series of prisms adjusted around a conical wheel, which willbe soon described, and are then received by the telescope spectrum, which is formed at the focus of the object-glassof this telescope, is examined with eyepieces of different mag-nifying powers in the usual way. The object-glasses of the tele-scopes are 2^ inches in diameter, and have a focal length of 15^inches. They rest in Ys, and are provided with spirit levels andadjusting-screws. The frames which hold
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Keywords: ., bookcentury1800, bookdecade1840, bookidlondon, booksubjectscience
