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THE POPULAR SCIENCE MONTHLY. 



ing to what metal was used. With Wood's alloy, which is very fusi- 

 ble, the projections that fell on the edge of the crater flowed away, 

 and left no trace of their passage. With the second alloy the pro- 



Fig. 1. Artificial Crater oetained with an Allot. 



jections 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 Allot. 



"The second experiment was marked by a very interesting inci- 

 dent. Two concentric circular areas were noticed, the one nearer to 

 the center being the higher. This was due to an interruption to the 



