RAREFACTION • DICCIONARIO INGLES.COM • Definition of Rarefaction

... and shortly reach another and still loftier quebrada. Icicles hang from the rocks, the pools of the streams are frozen; we have reached an altitude as high as the summit of Mont Blanc, and our distended lips, swollen hands, and throbbing temples show how great is the rarefaction of the air. ...

— Mr. Fortescue • William Westall

... obstruction. The resistance of mere rising ground or dense vegetation to a free movement of the air from low-lying levels performs an obstructive office similar to that of the walls and roofs of houses, and with like effect. The invariable condition of unhealthy seasons and days is a state of rarefaction and stagnation of the atmosphere, when the poison-freighted vapor cannot be lifted and dispersed, and every one complains of the sultry, close, "muggy" (meaning murky) feeling of the air. Few reflect, when fretted by the boisterous winds ...

— Scientific American Supplement, Vol. XV., No. 388, June 9, 1883 • Various