. The London, Edinburgh and Dublin philosophical magazine and journal of science. e of the centre, the slit imagewould then fall on the black surface and the reflected lightwould be focussed on the thermopile by the hemisphericalmirror. The galvanometer deflexions in these two positionsof the thermopile would measure the intensities of theincident and reflected radiation respectively. In order tointerchange different black surfaces or to interpose screensin front of the thermopile only, the thermopile with thesurface attached could be taken out and afterwards replaced * Communicated by the Aut
. The London, Edinburgh and Dublin philosophical magazine and journal of science. e of the centre, the slit imagewould then fall on the black surface and the reflected lightwould be focussed on the thermopile by the hemisphericalmirror. The galvanometer deflexions in these two positionsof the thermopile would measure the intensities of theincident and reflected radiation respectively. In order tointerchange different black surfaces or to interpose screensin front of the thermopile only, the thermopile with thesurface attached could be taken out and afterwards replaced * Communicated by the Author. A preliminary communicationappeared in the Physikalische Zeitschrift, xi. p. 316 (1010). f Angstrom, Ofversigt of K. Forhandl. Stockholm, 283 (1898). X Fery, C. R. 148. p. 777 (1909). § Modification of method bv which Paschen made his bolometerblacker. See Ber. Berl. Akad. d. Wiss. April 27th, 1899. 168 Mr. T. Royds on the Reflective in exactly the same position relative to the the external optical arrangement was altered, the Fisr. thermopile was placed in its first position to receive the lightdirectly, and the external concave mirror so adjusted thatthe slit image tell on the thermopile slit which could be seenfrom behind through a window. In this way, it was notnecessary to alter the two positions of the thermopile. Thesetwo positions were determined once for all by experimentand checked at intervals. The continuous line in fig. 2shows the deflexions for a matt reflecting surface as thethermopile was gradually displaced in the great circle of thehemisphere. The distance between the incident slit imageand its image reflected in the hemisphere was made as smallas possible in order to have good definition ; this distanceamounted to 25 mm., the diameter of the hemisphere being5 cm. The thermopile slit was 1 mm. wide, the image ofthe illuminated slit falling just within it. A series ofLangley diaphragms was placed in front of the ope
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
