274 LIFE AND DEATH. 



pletcd, and the metal attains the definite equilibrium 

 corresponding to the conditions to which it is exposed. 

 Though there may be discussions concerning the 

 extent of the transformations to which it is subjected, 

 though some believe they affect the chemical con- 

 dition of the alloy, while others limit its power to 

 physical effects, it is nevertheless true — and this 

 brings us back to our subject — that the mass of these 

 metals is at work, and that it only slowly attains the 

 phase of complete repose, 



TJie Slozu Re-establishment of Equilibruun. Re- 

 sidual Effect. — These operations by which the physical 

 characters of metals are changed, and by which they 

 are adapted to a variety of industrial needs — com- 

 pression, hammering, rolling, stretching, and torsion — 

 have an immediate, very apparent effect; but they 

 have also a consecutive effect, slowly produced, much 

 less marked and less evident. This is the "residual 

 effect," or " Nachwirkung" of the Germans. It is not 

 without importance, even in practical applications. 



Heat also creates a kind of forced egicilibriiim. 

 This becomes but slowly modified, so that a body 

 may remain for a long time in a state which is, how- 

 ever, not the most stable for the conditions under 

 which it is considered. The number of these bodies 

 not in equilibrium is as great as that of the substances 

 which have been exposed to fusion. All the Plutonic 

 rocks are in this condition. Glass presents a con- 

 dition of the same kind. Thermometers placed in 

 melting ice do not always mark the zero Centigrade. 

 This displacement of the zero point falsifies all 

 records if care is not taken to correct it. The 

 correction usually requires prolonged observation. 

 The theory of the displacement of the therrnometric 



