The London, Edinburgh and Dublin philosophical magazine and journal of science . rbing medium into successivestrata of identical thickness and chemical constitution. Let A be a source of radiant heat or light whose intensityis reduced by passage through the first stratum to (let ussuppose) a fraction of the original represented by p, so thatwhat was A becomes Ap. Then, since the second stratumis identical with the first in constitution and amount, andmust (it is assumed) have an identical effect, it will, onBouguers hypothesis, transmit p of what enters it, and Ap2will emerge from the second,
The London, Edinburgh and Dublin philosophical magazine and journal of science . rbing medium into successivestrata of identical thickness and chemical constitution. Let A be a source of radiant heat or light whose intensityis reduced by passage through the first stratum to (let ussuppose) a fraction of the original represented by p, so thatwhat was A becomes Ap. Then, since the second stratumis identical with the first in constitution and amount, andmust (it is assumed) have an identical effect, it will, onBouguers hypothesis, transmit p of what enters it, and Ap2will emerge from the second, and so on, the fraction p trans-mitted by the unit of thickness (the coefficient of transmis-sion ) being evidently the common ratio of a geometricalprogression, so that if the original heat be A, the amount ofheat after passing through e strata will be Ape, and the amounttransmitted at any point will be proportional to the ordinateof a logarithmic curve. To apply this to the estimate of the heat outside the atmo-sphere (i. e. before absorption), let iSJ be a small portion of. the earths surface, and EK the upper surface of the atmo-sphere, which is here supposed to be of uniform density andconstitution. (The effects of the actually unequal density ofsuccessive strata can, it is assumed, be calculated and allowedfor.) Let S be the observers station, then ES would be thedirection of a ray where the sun is in the zenith ; and, to fixour ideas, letFS = 2ES, GS = 3 ES, KS = 4ES, &c. The * Bouguer, TraiU de la lumtire, Paris, 1760. 292 Mr. S. P. Langley on the Amount original heat A would become Ap after passing through onestratum (ES) ; and, according to what has been assumed, itwould become (when the suns zenith distance became ESF)Ap2 after absorption by the two strata between F and S, Ap3after absorption by the three strata between Gr and S; &c. A,the original heat, and p, the coefficient of transmission, areunknown ; but if we make an observation of the heat actuallyreaching S
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Keywords: ., bookcentury1800, bookdecade1840, bookidlondon, booksubjectscience
