A UNIVERSE OF MIND-STUFF 



people do who are dancing Sir Roger de Cover- 

 ley, they join hands, swing around, and then 

 fly away in different directions. All these mole- 

 cules are constantly changing the direction of 

 each other's motion ; they are flying about with 

 very different velocities, although, as I have 

 said, their mean velocity is about seventeen 

 miles a minute. If the velocities were all marked 

 off on a scale, they would be found distributed 

 about the mean velocity just as shots are dis- 

 tributed about a mark. If a great many shots 

 are fired at a target, the hits will be found thick- 

 est at the bull's-eye, and they will gradually 

 diminish as we go away from that, according to 

 a certain law which is called the law of error. It 

 was first stated clearly by Laplace ; and it is 

 one of the most remarkable consequences of 

 theory that the molecules of a gas have their 

 velocities distributed among them precisely ac- 

 cording to this law of error. In the case of a 

 liquid, it is believed that the state of things is 

 quite different. We said that in the gas the 

 molecules are moved in straight lines, and that 

 it is only during a small portion of their motion 

 that they are deflected by other molecules ; but 

 in a liquid we may say that the molecules go 

 about as if they were dancing the grand chain 

 in the Lancers. Every molecule after parting 

 company with one finds another, and so is con- 

 stantly going about in a curved path, and never 

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