These streams continue to flow in winter as well as in summer, although in less quantity; and it is this process which chiefly prevents the glacier from increasing in size; for the melting at the surface is, in comparison, very inconsiderable, even in summer, the wind being cold, the sun having little power, and slight frosts being frequent during the night. It is also this melting beneath the ice (subglacial, suppose we call it) which loosens the ice from the ground, and occasions, or rather permits, the perpetual downward movement, with which "The glacier's cold and restless mass Moves onward day by day." 276. But more forcible and striking evidence is afforded by experiments made in mines of great depth. Between 60 ft. and 80 ft. down, the temperature of the earth is, I believe, the same at all times and in all places; and below this depth it gradually increases. Near Bex, in the Valais, there is a perpendicular shaft 677 ft. deep, or about 732 ft. English, with water at the bottom, the temperature of which was ascertained by Saussure. He does not tell us whether he used Reaumur's or the centesimal thermometer; but the result of his experiment was this:--In a lateral gallery, connected with the main shaft, but deserted, and, therefore, unaffected by breath or the heat of lamps, at 321 ft. 10 in. below the surface, the temperature of the water and the air was exactly the same, 11-1/2 deg.; or, if the centesimal thermometer was used, 52-4/5 Fahr.; if Reaumur's, 57-7/8 Fahr.