The Bourhan-Bota mountain has this remarkable particularity, that the deleterious vapour for which it is noted, is only found on the sides facing the east and the north; elsewhere, the air of the mountain is perfectly pure and respirable. The pestilential vapours themselves would appear to be nothing more than carbonic acid gas. The people attached to the embassy told us that when there is any wind, the vapours are scarcely perceptible, but that they are very dangerous when the weather is calm and serene. Carbonic acid gas being, as the reader is aware, heavier than the atmospheric air, necessarily condenses on the surface of the ground, and remains fixed there until some great agitation of the air sets it in movement, disperses it in the atmosphere, and neutralizes its effects. When we crossed the Bourhan-Bota, the weather was rather calm than otherwise. We remarked, that when we were lying on the ground, respiration was much more difficult; when, on the contrary, we raised ourselves on horseback, the influence of the gas was scarcely felt. The presence of the carbonic acid rendered it very difficult to light a fire; the argols burned without flame, and threw out great quantities of smoke. As to the manner in which the gas is formed, or as to whence it comes, we can give no sort of idea. We will merely add, for the benefit of those who are fond of seeking explanations of things in their names, that Bourhan-Bota means Kitchen of Bourhan; Bourhan being a synonyme of Buddha. During the night we passed on the other side of the mountain, there fell a frightful quantity of snow. Our companions, who had not ventured to ascend the entire mountain at once, rejoined us in the morning; they informed us that they had effected the ascent of the upper portion of the mountain easily enough, the snow having dispersed the vapour.