On the Dark Plane Which is Formed Over a Heated Wire in Dusty Air 1

Abstract

IN the course of his examination of atmospheric dust as rendered evident by a convergent beam from the electric arc, Prof. Tyndall noticed the formation of streams of dust-free air rising from the summits of moderately heated solid bodies (Proc. Roy. Inst., vol. vi. p. 3, 1870). “To study this eftect a platinum wire was stretched across the beam, the two ends of the wire being connected with the two poles of a galvanic battery. To regulate the strength of the current a rheostat was placed in the circuit. Beginning with a feeble current, the temperature of the wire was gradually augmented; but before it reached the heat of ignition, a flat stream of air rose from it, which, when looked at edgeways, appeared darker and sharper than one of the blackest lines of Fraunhofer in the solar spectrum. Right and left of this dark vertical band the floating matter rose upwards, bounding definitely the non-luminous stream of air.” . . .