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    Naturevolume 43pages4445 (1890) | Download Citation



    MEASURES OF LUNAR RADIATION.—The Proceedings of the American Academy of Arts and Sciences (vol. xxiv.) contains an account of some measures of lunar radiation made by Mr. C. C. Hutchins by means of a new thermograph. This instrument consists of a single thermal junction of nickel and iron placed in the focus of a small concave mirror. The author finds that the condensing mirror fulfils the functions of multiplied junctions, while the single union rapidly attains thermal equilibrium. A comparison was made between the thermograph and a thermopile of forty-eight couples, the result being that the former was found about twelve times as sensitive as the latter. Measures of the radiating power of some rocks, mostly of volcanic origin, show a remarkable uniformity. If the radiation from a blackened surface of quartz be taken as 100, the lowest radiating power is possessed by common white pumice, and is represented by 71˙3. The temperature at which the measures were made was near 100° C. The measures of lunar radiation were made with an arrangement similar to that of a Herschel's telescope with the thermograph in place of an eye-piece. The results of the experiments indicate that the heat which our planet receives from the moon is to that of the sun as 1 is to 184,560. Some observations were made during the lunar eclipse of January 28, 1888, for the purpose of determining whether our atmosphere allowed radiations from the heated lunar surface to pass through it. When the moon was in the penumbra, the reading of the galvanometer scale was 254˙4, nineteen minutes before totality it was 11˙2, eight minutes before totality it was 7˙3, and the mean of thirty readings taken during the total phase gave the value 2˙09. The inference drawn from these observations is, that all but a minute portion of the rays from the lunar soil and rock are cut off by our atmosphere, for it seems impossible to conceive that a surface like that of the moon, upon which the sun has been shining for many days, should suddenly cease to radiate when the sun's light is withdrawn. A comparison of lunar rays with solar rays reflected from various rocks shows that the selective absorption by the rocks is altogether insufficient to explain the great absorption of the lunar rays observed during the eclipse. An attempt has been made to construct a curve representing the change of transmission of lunar rays by our atmosphere with changes in the altitude of the moon. The measures show that our atmosphere, at the ordinary pressure, transmits 89˙25 per cent, of the vertical lunar beam.

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