Before arriving at this explanation, however, we experimented to see if the phenomenon was caused by the air having become slightly electrified, perhaps by reason of its having streamed as an upward convection current over the surface of the warm solid, at which we were looking, in a thick smoky atmosphere, in the concentrated light of an electric arc. We therefore purposely electrified the rod, to see what that would do, and we found to our surprise, directly the electric machine was turned, that the smoky atmosphere almost instantaneously disappeared, and the box became quite clear. This experiment, after development, though described in July, 1883, was shown in public for the first time at the Dublin Royal Society (_Nature_, April 24, 1884), and subsequently at the British Association meeting in Montreal[20] in 1884, and was applied to the experimental clearing of rooms from dense smoke or fume. It has often been shown since, by Mr. Swan and others, and has become fairly well known.[21] [19] “Dimensional Properties of Matter,” _Phil. Trans._, 1879. [20] Evening Lecture on “Dust,” by the writer, see _Nature_, Vol. 31, p. 265; also _Journal_ of the Royal Institution, May, 1886. [21] Apparatus for the purpose is now in the catalogue of Messrs. Ducretet, of Paris, but they supply a pair of combs of points. It makes a more interesting experiment if only one point is used, in a moderate space, and the electric supply regulated so as not to hurry the disappearance of the smoke too quickly, but to exhibit the stages of aggregation which precede the final disappearance by deposition. Any kind of smoke serves, but a bit of magnesium ribbon burnt under a bell jar is cleanly and effective. It should be looked at in a window or other good light, of course. The next observation of cohesion under electrical influence was made by the writer in 1889, while working at the protection of telegraphic instruments and cables from lightning,--a research which resulted in the use of choke coils as supplementary to the air gaps of the ordinary lightning guard, and thus to the forms of instrument constructed by Dr. Alex. Muirhead for telegraphic work in this country, and to the supplementary additions adopted by the Westinghouse Company for their non-arcing guards adapted to electric light and power installations in America. The observation of cohesion was a bye-issue, noticed when the knobs of the lightning guard were brought too close together.[22] [22] _Journal_ of the Institution of Electrical Engineers for 1890, pp. 352-4.