THE ?MATERIAL EJECTED. Tile quantity of ma terial ejected in the course of eruption is Or dinarily dependent upon the force or violence of the eruption, and the period of its continuance. Skaptar in its great eruption of 1783, threw out a mass of lava the cubical contents of which are thought to have equaled the bulk of the Mont Blanc massif. In the historic eruption of Vesuvius of the year 79 there was no lava flow, but the discharge of fragmental products (cinders and ashes) was very large, burying,. as is well known, a considerable portion of Cam pania with diThris several feet in thickness. The cataclysm of Krakatoa in 1883 was responsible for the extrusion of material which, it has been thought, could not have measured less than 4.3 cubical miles; and this again, we are informed by some geologists. could hardly have been more than the one-hundredth part of the material that was thrown out by Temboro, on the island of Sumbawa, in 1815. It seems not unlikely that on certain days of its eruptions in May and August, I902, the ejecta of chiefly ashes, more than equaled in bulk the quantity of sediment discharged by the Mississippi River in the course of a full year. The projectile force of eruption is such that the lighter materials of eruption are thrown many miles into the air. where they may be kept suspended for months or even years, as in the ease of the Krakatoa eruption, moving alma with the upper atmospheric currents, and giving rise, through the sifting out and reflection of the sun's rays, to those remarkable phenomena which are known as the 'red glows' or 'volcanic after glows.' These, made beautiful by their intense
illumination, and impressing the beholder at times with the aspect of a vast conflagration, usually follow the true sunset by the period of about a half-hour (20-40 minutes), and rise to a position in the sky possibly exceeding 45° above the horizon. The afterglows of the Kraka toa eruption, which were the first to be carefully observed, were thought to have been deflected from dust partieles at a height above the earth's surface of from 30 to 50 or even 70 miles, and were continued for a period of con siderably over a year. The afterglows following, sonic of the Antillean eruptions were less bril liant and less continuous, and were seemingly thrown from a height not exceeding 20 to 25 miles, and at times, possibly, of only S to 15 miles. In both eases the phenomena were ob served over widely removed portions of the earth's surface, which led to the conclusion that they were visible over the entire circumfer ence of the globe, appearing at different localities at different times, depending upon the rate of travel of the suspended dust particles. Those from Krakatoa traveled with a general velocity of from 50 to 70 miles per hour, or more than twice that which impelled the particles from Hel6e. The course of travel was in both cases from east to west.