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THE POPULAR SCIENCE MONTHLY.
ing to what metal was used. With Wood's alloy, which is very fusible, the projections that fell on the edge of the crater flowed away, and left no trace of their passage. With the second alloy the projections
Fig. 1.—Artificial Crater obtained with an Alloy.
all continued visible, and gave a rent aspect to the crater. Moreover, since the warm air was not hot enough to melt the metal, the projections might eventually overhang the bottom, as appears in Fig. 1.
Fig. 2.—Action of a Current of Air on a Melted Alloy.
"The second experiment was marked by a very interesting incident. Two concentric circular areas were noticed, the one nearer to the center being the higher. This was due to an interruption to the
