IDENTICAL CHANGES 



and the tempering of steel is not a chemical Process. 

 In the tempered steel the iron is still iron and the 

 carbon is still carbon. 



The sudden cooling contracts the steel, this is 

 certain. The sudden cooling hardens the steel, 

 that also is certain. And in sudden cooling the 

 fibres of the steel become crystalline. Equally cer- 

 tain it seems that in the tempered steel the atoms, 

 molecules or crystals cannot turn clear around or 

 change end for end. Then while the magnetizing 

 of steel does not in the least affect the temper, it 

 yet causes a further contraction in the steel. 



And since the whole process of magnetizing may 

 be done by mechanical means alone, therefore, the 

 particles of the steel undergo a change of relative 

 position only in the process of magnetizing. A 

 permanent magnet is generally composed of steel, 

 carbon and iron. And carbon and iron generally 

 compose the most part of magnetic ores or meteors 

 or Loadstones. Because of their high melting 

 points and great cohesion it is most probable that 

 both the atoms of carbon and iron are particularly 

 long in proportion to their breadth. 



While a form built up of indivisible spheres can- 

 not be a true sphere or rectilineal solid (Prop. X, 

 B. 1), yet it may approach the general outline of 

 such solid bodies. From various indications it 

 would appear that the atom of carbon resembles 

 an elongated cylinder in general outline, while the 

 atom of iron resembles a triangular Pyramid. 

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