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to the interior of the circle But, if he desires to turn his face* 

 always inwards, he must turn round in the same direction as he 

 walks round." The logic here is the same as Mr Buchanan's, 

 and is just a new version of the old fallacy, which I have 

 already detected and exposed ; — taking for granted, as an in- 

 dubitable fact, what is nevertheless a physical impossibility, — 

 the presenting of " every part of its circumference in succes- 

 sion" to the centre of its orbit, by a globe revolving in an or- 

 bit, without rotating on its axis. Our walking gentleman him- 

 self shall prove this. Let him be tied to the centre of his cir- 

 cle, as the moon is to hers by her centripetal radius of gravi- 

 tation, and then let him walk round the circle, if he can, with 

 his face constantly pointed in the same direction to a distant ob- 

 ject outside. He will find the latter condition impossible unless 

 he turn backward on his own axis, simultaneously with his for- 

 ward orbital movement. Suppose him to be tied to his circle by 

 a cord fixed round his waist. As he moves round his orbit he 

 will find that the noose will make him keep the same side, or 

 face, or back^ as the case may be, directed constantly to the cen- 

 tre of the circle, unless he draw himself continually away from 

 its knot and the radius-vector by moving " left shoulders for- 

 ward." One of two things seems perfectly certain : either the 

 noose and its knot revolve about the man, or the man turns back- 

 ward on his own axis within the noose ; but the knot being fixed 

 to the radius, and the radius to the centre of the circle, it is quite 

 obvious that they cannot revolve about the man, therefore it 

 must be the man that retro-rotates within the noose. This has 

 been abundantly shown already, and is just another version of 

 the water in the basin. Let the walking gentleman turn round 

 again on his own axis, in the direction of " right shoulders for- 

 ward," within his noose, while going round his circle, and he 

 will find his face and back and two sides, in turn, or, in other 

 words, " every part of his circumference in succession," present- 

 ed to the centre of the circle, thereby completely disproving the 

 doctrine he was brought to prove, namely, that the moon's present- 

 ing the same hemisphere continually to the earth is the effect of 

 her rotation on her own axis, from west to east, the same direc- 

 tion which the experimenter had last taken, in his turning round. 

 The author of this cyclopa^diac article has just assumed that the 

 same eff'ectas would be produced by a person's moving first straight 

 forward along a given line, and then moving straight backward 

 to his starting point, would be produced were he obliged to go 

 out of his straight path round some intervening obstacle, such as 

 a round table placed upon the line. But, in the latter case, he 

 would be obliged, in going from north to south, for instance, to 

 shuffle out of his way to the left, and, in returning, to shuffle 



