. Report of the Expedition to Castellon de la Plana, Spain. er. In order to test this, the two halvesof the pile were simultaneously exposed to the same radiation. The deflectionobserved when the two halves were opposed was less than one-thousandthpart of the deflection obtained when the two halves were connected in thesame direction, the radiation remaining unchanged. This accuracy ofcompensation was very important for the method which it was proposed to 1905.] Eclipse Expedition to Castelldn de la Plana, Spain. 11 adopt. As a subsidiary test, the resistances of the two halves of the pile wer
. Report of the Expedition to Castellon de la Plana, Spain. er. In order to test this, the two halvesof the pile were simultaneously exposed to the same radiation. The deflectionobserved when the two halves were opposed was less than one-thousandthpart of the deflection obtained when the two halves were connected in thesame direction, the radiation remaining unchanged. This accuracy ofcompensation was very important for the method which it was proposed to 1905.] Eclipse Expedition to Castelldn de la Plana, Spain. 11 adopt. As a subsidiary test, the resistances of the two halves of the pile weremeasured, and found to be 4*56 and 4*62 ohms respectively. Exact equalityof resistance was not essential, but the result is satisfactory as showing howaccurately the mechanician, Mr. W. J. Colebrook, of the Koyal College ofScience, had succeeded in executing the design. As a result of this accuracy of compensation, the zero of the galvanometerremained extremely steady even under the most trying conditions, with the Fig. 1.—Coronal Thermopile. To Galvr,. (Galvf)Enlarged about 3 diameters. telescope exposed to full sunshine and surrounded by unequally heated was never any difficulty in taking accurate observations, provided thatthe sun was not allowed to shine directly on the eye-piece. At night, andduring totality, when the disturbing influence of the solar radiations wasabsent, it is hardly necessary to say that no trouble was experienced. Methods of Observation. The galvanometer employed with the coronal thermopile was of themovable-coil type with a plane mirror, 1 inch in diameter, reflecting theimage of a transparent millimetre scale at a distance of 3 metres into 12 Profs. H. L. Callendar and A. Fowler. [Oct. 19, a telescope of 2 inches aperture and 3 feet focal length. With this powerthe definition was so good that it was easy to read to a tenth of a millimetrewith certainty. The galvanometer was supported on a pier south of thetelescope and proved extreme
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