On the Absolute Measurement of the Total Amonnt of Radiation from the Whole Sky

[摘要] One of the authors, Kato, has constructed an apparatus for measuring the total amount of radiation from the whole sky after the same method as Ångström's pyrheliometer, in company with Mr. K. Sinozuka, a member of the trial manufacture department of delicate machinery attached to the Physical Institute of the Imperial University of Tokyo.The chief part of the apparatus is composed of three thermopiles. The elements which form these thermopiles are extremely thin foils of manganin and constantan. Each thermopile is made of 14 elements and has electric resistance of 12.11±0.015Ω, and it needs 9 sec till the full electro-motive force caused by the constant radiation is measured. It is laid on a circular disk of brass having a diameter of 22mm. Each element is 0.8mm broad, 12mm long and 10 microns thick.These three thermopiles are denoted as A, B and C for convenience' sake. Each of A and B is furnished with a thin foil of manganin; this foil is 19mm long, 2mm broad and 10 microns thick, and is blackened with soot of camphor and jointed to the high temperature part of the thermopile. A slit of 19mm length and 8mm breadth is mounted up on the thermopile and manganin foil. C is jointed by an extremely thin foil of manganin to the high temperature part, but this foil is not blackened and is covered with thin plates of copper. Other parts of the thermopile are of the same construction as those of A and C. The principle of measurement is on the whole the same as that of K. Ångström's electric compensation pyrheliometer, namely: A and C are exposed to the radiation, while the manganin plate of B is heated by electric current. When the heat energy which A receives from the radiation is equal to what B receives from the electric current, the thermoelectric currents generated in the thermopiles will be also equal. This two thermo-electric currents are compensated each other by the zero method making use of the pointing galvanometer. Let the length of the manganin plate be l, its breadth b, the absorption coefficient a, the electric resistance per unit length r, and the strength of the current i, then the heat which B receives from the current will be_??_per unit time, where J denotes the Joule's constant. If the total amount of radiation falling on a horizontal surface per unit area per unit time is q gram calories, the beat which the manganin plate of A receives will be qb_??_a. Equating the two values, we obtain the following formulae as the total amount of radiation fallng on a horizontal surface of the earth per unit area per minute: In this equation i will be determined by practical observation, and r and a must be determined experimentally. The result of the measurement is r=0.2446 and a=99.85%. Substituting these values, the equation becomes Q=17.499 i2 It is necessary to explain the usefulness of the thermopile C. When the pile A is heated by the radiation, its part between the manganin plate and the slit is also exposed to the radiation and the heat produced by the latter is conveyed to the active junctions by heat conduction. This effect should be by all means removed. The pile C, as its construction indicates, only produces the thermo-electric current by the above effect, because the active junctions are unable to receive the heat directly from the radiation. Accordingly, in the practical observation the pile A is exposed to the radiation, together with C, and if the thermoleectric current produced in the latter is reverse to that in the former, this combination of A and C may be compared with the thermo-electric current produced by B in which the manganin plate is heated by electric current. Next, B and C are exposed to the radiation, there also the two thermo-electric currents are reverse each other, and A is heated by the current.

[学科分类] 大气科学