. The London, Edinburgh and Dublin philosophical magazine and journal of science. in width ; the spark discharge was concealedbehind this. Two hypotheses immediately presented themselves : (a) weare dealing with a scattering of the shortest waves by the* Communicated bv the Author. 3 A2 708 Prof. R. W. Wood Neu air molecules or microscopical dust particles, as in case ofblue-sky ; (b) ultra-violet fluorescence of the air caused bythe absorption of the Schumann waves. As a matter of factneither hypothesis turned out to be tenable, but I mentionthem to show that they have been carefully consider
. The London, Edinburgh and Dublin philosophical magazine and journal of science. in width ; the spark discharge was concealedbehind this. Two hypotheses immediately presented themselves : (a) weare dealing with a scattering of the shortest waves by the* Communicated bv the Author. 3 A2 708 Prof. R. W. Wood Neu air molecules or microscopical dust particles, as in case ofblue-sky ; (b) ultra-violet fluorescence of the air caused bythe absorption of the Schumann waves. As a matter of factneither hypothesis turned out to be tenable, but I mentionthem to show that they have been carefully considered. If the emission of ultra-violet light by the air was merelya scattering, its spectrum should be identical with that of thespark : if, on the contrary, it is a fluorescence phenomenon,its spectrum would be totally different. In the spectro-scopic work it was necessary to get as close as possible to thespark, and yet run no risk of having its direct light enterthe slit of the instrument. To meet this requirement theapparatus shown in fig. 1 was constructed. A disk of Fig. aluminium, 3 mm. thick, was perforated with a hole 1*5 diameter and fastened to a short brass cylinder B. electrode C was carried by a screw D, whichpassed through the ebonite cap E. The spark dischargepassed between C and the inner rim of the hole in thealuminium disk. If the spark chamber is hermeticallysealed the explosive expansions of the air are apt to forcethe spark aureole, which is pale green in the case of thealuminium spark, out through the hole. The small lateraltube J prevents this, and serves as well for the introductionof various gases. The length of the spark must be soadjusted that no visible portion is forced out through thehole, when viewed from the position K. A second brass cylinder F, closed at the top and fitted Radiant Emission from the Spark. 709 with two lateral tubes H and G, can be screwed to the sparkchamber when it is desired to study the emission in dryf
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
