178 M. G. E. Svedelius.ora the Changes in the Length and 



Of the two curves in fig. 1 the upper represents the changes 

 in length taking place in a copper rod, and the lower one 

 those taking place in a Bofors wire containing 0'6 per cent, 

 of carbon when it is heated one minute and then left to cool. 

 The longitudinal curve for the copper rod shows, both during 

 heating and cooling, an even process. The longitudinal curve 

 for the steel rod has, on the contrary, two clearly appearing 

 jerks, an anomalous contraction during heating at D*, and an 

 anomalous expansion during cooling at D'f. 



The effect of the percentage of carbon upon the critical points 

 D and D'. — Referring to fig. 2, the longitudinal curves for 

 the rods of hard steel (Bofors, 9 per cent, carbon), soft 

 steel (Bofors, 0*5 per cent, carbon), and soft iron (Bofors, 

 O'l per cent.), show the following : — 



(i.) The contraction at D is considerably less than the ex- 

 pansion at D ; J. 



(ii.) The contraction at D begins just as soon after the com- 

 mencement of the heating — and consequently at about the 

 same degree of heat— in steel and soft iron, but lasts longer the 

 smaller the percentage of carbon is. 



The expansion at D' takes place earlier after extinguishing 

 the flame, and thus at a higher degree of heat, and is of 

 longer duration in soft iron than in steel. 



(iii.) The contraction at D and the expansion at D' are 

 greatest in soft steel, and less in hard steel and soft iron. 



The observations made by the aid of a telescope and scale 

 show that the anomalous changes of length increase in mag- 

 nitude with the increase of the percentage of carbon from 

 0*1 per cent, to 0*6 per cent., that they are of the greatest 

 value with # 6 per cent, of carbon, and decrease thereafter 

 with the increasing percentage of carbon from 0*6 per cent, 

 to 1*0 per cent, of carbon §. 



(iv.) The contraction at D seems in soft iron to consist of 

 two moments T> 1 and D 2 , of which the former begins at a 

 lower degree of heat and is of short duration. This is con- 



* First shown by Prof. W. F. Barrett, Phil. Mag. ser. 4, xlvi. (1873), 

 p. 472. 



t First shown by Mr. G. Gore, Phil. Mag ser. 4, xxxviii. (1869), p. 59. 



X Shown by Prof. Barrett, Phil. Mag. ser. 4, xlvi. (1873), p. 474. 



§ Contrary to my experience Prof. Barrett (Phil. Mag. ser. 4, xli. 

 1873, p. 475) and Herr Heim (Unters. iiber die Gore'schen P/iimomene, 

 1885, p. 31) have found the anomalous change during cooling appear 

 most strongly marked in hard steel, weaker in iron containing a low 

 percentage of carbon, and absent in very mild iron. 1 have, however, 

 not succeeded in finding any iron, except burnt m>n, in which the critical 

 points D and D' have not clearly appeared ; on the contrary, they have 

 always appeared weaker the first time the samples were heated. 



