. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. a projecting piece, a metal ring, inwhich can be supported capsules, b, for the burning sub-stances. In using this combustion-lantern, as I venture to term it,it is arranged in front ofthe ordinary lantern, in theoptic axis, with the dooropen as in the secondfigure, so that the lightfrom the optical lanterncan be passed through theslit s, and enable the latterto be focussed on thescreen, with its spectrumall in focus as describedin § 175. The opticallantern may then be turnedoff or removed.
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. a projecting piece, a metal ring, inwhich can be supported capsules, b, for the burning sub-stances. In using this combustion-lantern, as I venture to term it,it is arranged in front ofthe ordinary lantern, in theoptic axis, with the dooropen as in the secondfigure, so that the lightfrom the optical lanterncan be passed through theslit s, and enable the latterto be focussed on thescreen, with its spectrumall in focus as describedin § 175. The opticallantern may then be turnedoff or removed. The pow-der used is then placedin the capsule b, in a littleheap, a piece of cotton wickabout an inch long is stuckperpendicularly into it soas to be half-buried in thepowder; the wick is lighted, and the door shut; Prof. Wein-hold advises soaking the wick in lead chromate. As soon asthe flame reaches the powder it flames up, and gives excellentline-spectra, though for a short time only. Prof. Weinhold recommends the following mixtures aseffective. For sodium lines: 3 parts sodium nitrate, 1 part. 3io OPTICAL PROJECTION potassium chlorate, 1 part shellac. For calcium : 2 partschalk, 10 parts potassium chlorate, 3 parts shellac. Forstrontium: 3 parts strontium nitrate, 1 part potassic chlorate,1 part shellac. For barium: 3 parts barium nitrate, 1 partpotassium chlorate, 1 part shellac. The shellac to be powderedseparately from the salts, which are also to be rubbed downto powder, and the two mixed previous to use with a horn orwooden spoon. These methods are superior in effect to the use of glassrods, or sticks soaked in solution; besides which- the manipu-lation of such sticks in a jet is a very ticklish operation. 179. Reversed Spectrum Lines.—The absorption by vapoursof the same rays which they emit, is usually shown by sodium.
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
