. Contributions to the Centennial Exhibition. idence which Sir John Herschel places in the appli-cation of the law of inverse squares to the determinationof solar energy at given distances : The intensity of solarradiation is nearly seven times greater on ^fercury thanon Earth, and on Neptune 900 times less; the proportionof the two extremes being that of upwards of 5,600 : any one figure to himself the condition of our globewere the sun to be septupled, to say nothing of tlie greater 20G BABIANT HEAT. chap. x. ratio ! or were it diminislied to a seventli, or to a OOOth !It is true that,
. Contributions to the Centennial Exhibition. idence which Sir John Herschel places in the appli-cation of the law of inverse squares to the determinationof solar energy at given distances : The intensity of solarradiation is nearly seven times greater on ^fercury thanon Earth, and on Neptune 900 times less; the proportionof the two extremes being that of upwards of 5,600 : any one figure to himself the condition of our globewere the sun to be septupled, to say nothing of tlie greater 20G BABIANT HEAT. chap. x. ratio ! or were it diminislied to a seventli, or to a OOOth !It is true that, owing to the remarkable difference betweenthe properties of radiant heat as emitted from bodies ofvery exalted temperature as the sun, and as from such aswe commonly teim tvaiin, it is very possible that a denseatmosphere surrounding a planet, while allowing the excessof solar heat to its surface, may oppose a powerful obstacleto its escape, and that thus the feeble sunshine on a remoteplanet .may be retained and accumulated on its No doubt Pouillet would have felt as little hesitation asHerschel in determining by the application of the law ofinverse squares the temperature produced by solar radiationon Mercury. Chapter I. contains an elaborate demonstration,proving the correctness of this law with reference to radiat-ing spheres uniformly heated at the surface. The above diagram represents the orbits of the Earth,Venus, and Mercury, their relative mean distance from thesun being correctly drawn. The orbit of an imaginary bodyI, revolving at a distance of 10,000,000 miles from the solar CHAP. X. TEMrEi:ATVliE-&F THE SOLAR SURFACE. 207 centre, has also been introduced In the diagram, for the pur-pose of demonstrating that a body revolving round the sunat that distance would be exposed to a temperature gieatlyexceeding that which Pouillet assigns to the solar agreeing that the law of inverse squares holdsfor all distances, whether it be that of Nep
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