THE FORMATION OF LUNAR CRATERS. 495 



THE FORMATION OF LUNAR CRATERS. 



M JULES BERGERON says, in a paper communicated to the 

 . French Academy of Sciences, and republished in "La Na- 

 ture " : "I have noticed that when gases or vapors pass through a 

 mass having the consistency of paste, they leave behind them funnel- 

 shaped holes. Struck by the analogy which these holes present with the 

 craters of the moon, I have endeavored to reproduce the phenomena 

 on a larger scale. To simplify my experiments as much as possible, I 

 used alloys, melting at relatively low temperatures, taking first Wood's 

 alloy, of seven parts of bismuth, two of cadmium, two of tin, and two 

 of lead, which melts at about 158 Fahr. Having introduced into the 

 mass, melted in the salt-water bath, a current of warm air by means 

 of a tin pipe, I allowed it to cool slowly while the inflation of warm 

 air was still continued. The ebullition which took place reached all 

 the parts which were beginning to solidify and form a pellicle over 

 a considerable surface; and there was formed before me a large circle, 

 around which the edges gradually rose under the continued inflation, 

 till it began to assume the appearance of a crater. At the same time, 

 the metallic mass becoming thicker as the cooling went on, while it 

 was still blown out by the air, could no longer drive the solid particles 

 away from itself, and rose above the crater in such a way as to form 

 a cone, which grew visibly more prominent. The crater also became 

 more hollow, with its inner walls more inclined than the outer walls, 

 and I had before me a formation strikingly analogous to the craters 

 of the moon. The same phenomena were observed, whatever alloy I 

 employed. 



" Similar processes have possibly taken place on the moon. In- 

 stead of gas, the reliefs may have been produced by the vapors, which 

 rose freely from the body while it was in a fluid state ; but the super- 

 ficial part of the planet being cooled much more rapidly than the 

 interior, the lattei', still fluid, continued to emit vapors after the sur- 

 face had become quite thick. The vapors found their way along the 

 superficial envelope, and came out only at particular points, where, 

 doubtless, the process of solidification was least nearly accomplished. 

 The vapors may subsequently have been condensed, or absorbed, by 

 the substances constituting the rock of the moon. 



" As my first experiments were made in a capsule, the objection 

 might be made that the circular form of the crater was produced 

 under the influence of the shape of the walls of the vessel. To ob- 

 viate such criticism, I employed a rectangular basin, in which I melted 

 an alloy of four parts of lead, four of tin, and one of bismuth. The 

 phenomena were produced as in the former case ; but I found that 

 the aspect of the mass after the formation of the crater varied accord- 



