ما يقوله الناس - كتابة مراجعة

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المحتوى

طبعات أخرى - عرض جميع المقتطفات

عبارات ومصطلحات مألوفة

مقاطع مشهورة

الصفحة 132 - Prof. Stokes mentioned to me at Cambridge some time ago, probably about ten years, that Prof. Miller had made an experiment testing to a very high degree of accuracy the agreement of the double dark line D of the solar spectrum with the double bright line constituting the spectrum of the spirit-lamp burning with salt.
الصفحة 131 - ... be opaque with respect to heat radiated by themselves. Considering, therefore, the heat of any temperature to consist of heterogeneous rays, we may state the law thus : " The absorption of a plate equals its radiation, and that for every description of heat.
الصفحة 279 - An Essay on the application of Mathematical Analysis to the Theories of Electricity and Magnetism...
الصفحة 366 - ... the highest. If so, in case the vapour showed its presence by absorption but not emission, it follows, from the correspondence between absorption and emission, that at one temperature the dark line which would be the most sensitive indication of the presence of the substance would be A, at another C, at a third E. Hence, while I regard the facts you mention as evidence of the high temperature of the sun, I do not regard them as conclusive evidence of the dissociation of the molecule of calcium....
الصفحة 130 - ... same refrangibility which traverse it, seems readily to admit of a dynamical illustration borrowed from sound. We know that a stretched string which on being struck gives out a certain note (suppose its fundamental note) is capable of being thrown into the same state of vibration by aerial vibrations corresponding to the same note. Suppose now a portion of space to contain a great number of such stretched strings, forming thus the analogue of a "medium.
الصفحة 136 - I have never attempted to claim for myself any part of Kirchhoff's admirable discovery, and cannot help thinking that some of my friends have been over zealous in my cause.
الصفحة 130 - We know that a stretched string which, on being struck, gives out a certain note (suppose its fundamental note), is capable of being thrown into the same state of vibration by aerial vibrations corresponding to the same note. Suppose, now, a portion of space to contain a great number of such stretched strings, forming thus the analogue of a " medium." It is evident that such a medium, on being agitated, would give out the note above mentioned; while, on the other hand, if that note were sounded in...
الصفحة 133 - ... have its temperature raised by light from the source of the precise quality in question. In the atmosphere around the sun, therefore, there must be present vapour of sodium, which, according to the mechanical explanation thus suggested, being particularly opaque for light of that quality, prevents such of it as is emitted from the sun from penetrating to any considerable distance through the surrunding atmosphere. The test of this theory must be had in ascertaining whether or not vapour of sodium...
الصفحة 302 - Now conceive the periodic time of tlii' motion to be continually diminished. Gradually the alternation of movement becomes too rapid to permit of the full establishment of the merely local reciprocating flow ; the air is sensibly compressed and rarefied, and a sensible sound-wave (or wave of the same nature, in case the periodic time be beyond the limits suitable to hearing) is propagated to a distance.

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