emerges from the icy regions of the Caucasus into the wooded hills, gentle slopes, sunny meadows, and neatly fenced barley-fields. Compared with the warrens or stone-heaps which serve the Tartars of the northern valleys for dwellings, even the towered villages have at a distance a false air of civilization. Suanetia in June, in the flower-time of the rhododendrons and azaleas, and again in October, when the azalea-leaves are red, and the birches golden against fresh autumn snows, must be one of the wonders of the world. Spaciousness, sunniness, variety, are the constant qualities of Suanetian landscapes. The great basin of the Ingur, forty miles long by ten to fifteen broad, is broken by no ridges that approach the snow-line, and the long, undulating, grassy spurs that divide the glens, in place of narrowing the horizon, furnish in their soft lines the most effective contrast possible to the icy peaks and rigid precipices of Shkara and Tetnuld, of Ushbe and the Leila. From the varied beauty of forests and flowers the eyes are carried at once to the pure glaciers, which hang like silver stairs on the green lower slopes of the snowy chain. The atmosphere has none of the harshness of that of Switzerland in summer. The breezes from the Black Sea bring up showers and moisture to soften the outlines and color the distances; the wind from the steppe suffuses the air with an impalpable haze, through which the great peaks glimmer like golden pillars of the dawn.
By Prof. S. P. LANGLEY.
THE first five years of this century are notable in the history of radiant energy, not only for the work of Leslie, and for the observation by Wollaston, Ritter, and others, of the so-called "chemical" rays beyond the violet, but for the appearance of Young's papers, re-establishing the undulatory theory, which he indeed considered in regard to light, but which was obviously destined to affect most powerfully the theory of radiant energy in general.
We are now in the year 1804, or over a century and a quarter since the corpuscular theory was emitted, and during that time it has gradually grown to be an article of faith in a sort of scientific church, where Newton has come to be looked on as an infallible head, and his views as dogmas, about which no doubt is to be tolerated; but if we could go back to Cambridge in the year 1668,
- President's address before the American Association for the Advancement of Science, at Cleveland, Ohio, August 15, 1888. Reprinted from "Science."