Identifier: londonedinburg6211911lond (find matches)
Title: The London, Edinburgh and Dublin philosophical magazine and journal of science
Year: 1840 (1840s)
Authors:
Subjects: Science
Publisher: London : Taylor & Francis
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ilter—showedvery irregular character. Nevertheless, it was evident thatthe main element of the investigated radiation was suppliedby a radiation of about the same mean wave-length as thatresulting from the Welsbach mantle with this arrangement.But as soon as a 15 mm. thick layer of quartz was inserted,the aspect was changed. The first minimum, which hadbeen observed for unfiltered radiation at a thickness of theair-film of about 5 divisions of the drum* (26 //,), now didnot appear before a thickness of the layer of air of 8 divi-sions (42 fju). If the thickness of the inserted layer of quartzwas increased to 42 mm., the first minimum appeared onlyat a distance of the interferometer plates of about 13 divisions(68 a*). At the same time the interference curve showed amuch smoother course. The originally observed irregularmaxima and minima had nearly quite disappeared ; and,besides the mentioned minimum at 13 divisions, in someseries of observations a faintly marked maximum appeared in
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o 10 the further course of the curve. Such an interferometer-carve is exhibited in the accompanying figure (curve a).Carve (6) of the same figure was observed in the same waywith insertion of the 2 mm. thick plate of amorphous quart/::curve (c) with insertion of the black cardboard (0*4 mm.thick). Curve (c) shows the wave-character most distinctly.Here the minimum lies at 15 divisions (784/a) and the* One division of the drum to 523ft. 694 Long Waves emitted by the Quartz Mercury Lamp. maximum at 30 is more conspicuous than in the otlier curves.But even in this curve an accurate determination of thesepoints is very difficult. The assumption is certainly justi-fiable, that the radiation filtered through black cardboardcontains a greater amount of this long-waved part than itdoes after purification by the quartz-filter. We had alreadydeduced this fact from the results of the absorption-table. It is still an open question, whether this long-wavedradiation consists of several nearly homog

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