Digitale Ausgabe
Download
| TEI-XML (Ansicht) | |
| Text (Ansicht) | |
| Text normalisiert (Ansicht) |
Ansicht
| Textgröße | |
| Originalzeilenfall ein/aus | |
| Zeichen original/normiert | |
Zitierempfehlung
Alexander von Humboldt: „Nocturnal increase of Sounds“, in: ders., Sämtliche Schriften digital, herausgegeben von Oliver Lubrich und Thomas Nehrlich, Universität Bern 2021. URL: <https://humboldt.unibe.ch/text/1820-Sur_l_accroissement-11-neu> [abgerufen am 19.04.2024].
URL und Versionierung
|
Permalink: https://humboldt.unibe.ch/text/1820-Sur_l_accroissement-11-neu |
| Die Versionsgeschichte zu diesem Text finden Sie auf github. |
| Titel | Nocturnal increase of Sounds | ||||||
|---|---|---|---|---|---|---|---|
| Jahr | 1822 | ||||||
| Ort | London | ||||||
|
Nachweis in: The Annual Register, or a View of the History, Politics, and Literature, for the Year 1821 (1822), S. 690–691.
|
|||||||
| Sprache | Englisch | ||||||
| Typografischer Befund | Antiqua; Spaltensatz; Auszeichnung: Kursivierung; Fußnoten mit Asterisken. | ||||||
|
Identifikation |
|||||||
Statistiken
|
|||||||
|690|
|Spaltenumbruch|
—Humboldt accounts for the in-crease of sounds during the night,by observing, that the presence ofthe sun affects the propagationand intensity of sound by theobstacles opposed to its trans-mission by currents of air of dif-ferent densities and partial un-dulation—the result of the un-equal heating of various parts ofthe earth’s surface. In air at rest,whether it be dry, or mixed withelastic vapours equally distributed
|Spaltenumbruch| through it, the sonorous undula-tion is propagated without diffi-culty. But when this air is crossedin every direction by small cur-rents of a warmer temperature,the sonorous undulation dividesinto two waves, at the spot wherethere is the most sudden changein the density of the medium;thus producing partial echoes,which weaken the body of sound,because one of the sonorous wavesis reflected back upon itself. Thetheory of these partitions of so-norous waves has been explainedby M. Poisson.* It is not, there-fore, the motion of the passage ofthe particles of air from belowupwards, nor the small obliquecurrents of this fluid that we con-sider as opposing, by impulse,the propagation of the sonorouswaves. A stroke or impulse im-pressed on the surface of theliquid will form circles around theimpinging centre, even when theliquid is in agitation. Severalkinds of waves may cross in air,as well as in water, without in-terfering with each other; but thetrue cause of the less intensity ofsound in the day-time appears tobe the want of homogeniety in theelastic medium. There is at thistime a sudden change of densitythroughout, produced by smallcurrents of air, of a high tempe-rature, rising from portions of theearth’s surface that are unequallyheated. The sonorous waves arethen divided in the same manneras luminous rays are refracted,and form a mirage of soundwherever strata of air of unequaldensity are contiguous. A dis-tinction must be kept between the
intensity of sound or of light, and
* Ann. de Chimie, t. 7.|691| |Spaltenumbruch| the direction of the sonorous orluminous wave. When thesewaves are propelled across strataof different densities two simulta-neous effects will be produced—there will be a change in thedirection of the wave, and extinc-tion of light or sound. The re-flection that accompanies eachrefraction weakens the intensityof light; the separation of thesonorous wave causes partialechoes, and that portion whichreturns on itself becomes insen-sible to our ear, in weak noises,at the spot where the density ofthe medium suddenly changes.In the mirage with double images,that which has undergone refrac-tion contiguous to the earth is al-ways weaker than the direct image.Strata of fluids, of very differentdensity, may so alternate, thatthe primitive direction of the lu-minous or the sonorous ray willremain the same, but the intensityof the ray will be not the lessweakened on that account. Du-ring the night the surface of theearth cools; the parts coveredwith grass, or with sand, take thesame temperature: the atmos-phere is no longer crossed bycurrents of hot air rising ob-liquely or vertically in every di-rection. The medium being nowbecome more homogeneous, thesonorous wave passes with lessdifficulty, and the intensity ofsound increases, as the separa-tions of the sonorous waves andechoes become less frequent.
Nocturnal increase of Sounds.
* Ann. de Chimie, t. 7.|691| |Spaltenumbruch| the direction of the sonorous orluminous wave. When thesewaves are propelled across strataof different densities two simulta-neous effects will be produced—there will be a change in thedirection of the wave, and extinc-tion of light or sound. The re-flection that accompanies eachrefraction weakens the intensityof light; the separation of thesonorous wave causes partialechoes, and that portion whichreturns on itself becomes insen-sible to our ear, in weak noises,at the spot where the density ofthe medium suddenly changes.In the mirage with double images,that which has undergone refrac-tion contiguous to the earth is al-ways weaker than the direct image.Strata of fluids, of very differentdensity, may so alternate, thatthe primitive direction of the lu-minous or the sonorous ray willremain the same, but the intensityof the ray will be not the lessweakened on that account. Du-ring the night the surface of theearth cools; the parts coveredwith grass, or with sand, take thesame temperature: the atmos-phere is no longer crossed bycurrents of hot air rising ob-liquely or vertically in every di-rection. The medium being nowbecome more homogeneous, thesonorous wave passes with lessdifficulty, and the intensity ofsound increases, as the separa-tions of the sonorous waves andechoes become less frequent.