could they do that?" Ken exclaimed. "Metals can't flow like liquids."
"They can if the conditions are right. When steel is heated to a sufficiently high temperature, it flows like water."
"But that's not the case here!"
"No, it isn't, of course. At lower temperatures the molecules of a solid do not possess the energy of motion which they have in a liquid state. The metallic surface of a piece of cold steel has a certain surface tension which prevents the escape of the relatively low-energy molecules; thus, it has the characteristics we ascribe to a solid."
"Then what has happened in this case?" Joe asked. "Are you able to tell?"
Professor Maddox nodded. "The photographs show us what has happened, but they reveal nothing about how or why. We can see the surface tension of the two pieces of metal has obviously broken down so that the small energy of motion possessed by the molecules has permitted them to move toward each other, with a consequent mixing of the two metals. It has turned them quite literally into a single piece, the most effective kind of weld you can imagine."
"What would cause the surface tension to break down like that?" Ken asked. 
"That is what remains for us to find out. We don't have the faintest idea what has caused it. It becomes especially baffling when we recall that it has happened, not in a single isolated instance, but all over the world."
"You would think the metals would have become soft, like putty, or something, for a thing like that to happen to them," said Joe. 
"It would be expected that the hardness would be affected. This is not true, however. The metals seem just as hard as before. The effect of mixing seems to take place only when the metals are in sliding motion against one another, as in the case of a piston and cylinder, or a shaft and a bearing. The effect is comparatively slow, taking place over a number of days. The two surfaces must break down gradually, increasing the friction to a point where motion must cease. Then the mixing continues until they are welded solidly to each other."
Ordinarily, the dusk of evening would have fallen over the landscape, but the blaze of the comet now lit the countryside with an unnatural gold that reflected like a flame through the windows and onto the faces of the men and boys in the laboratory. 
"As to the cause of this phenomenon," Professor Maddox said with an obviously weary deliberation in his voice, "we can only hope to find an explanation and a cure before it is too late to do the world any good."
"There can't be any question of that!" said Ken intensely. "The resources of the whole scientific world will be turned on this one problem. Every industrial, university, and governmental laboratory will be working on it. Modern science can certainly lick a thing like 

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