Temperature on Modulus of Rigidity of Solid Metals. 413 



After the experiment we examined their microstructures, 

 and found that, notwithstanding that hydrogen gas was 

 constantly passed through the furnace, these steels were 

 somewhat decarburized. The percentage of carbon was, 

 after the microscopic estimation, as follows : — 



Steel 0*55 per cent. C. contains 0*4 per cent. C. 

 „ 0*90 per cent. C. contains 0*8 per cent. C. 

 ,, 1'30 per cent. C. unknown. 



The last steel underwent, after experiment, the spheroidi- 

 zation of cementite, so that we could not accurately determine 

 the degree of decarburization. The values of rigidity of 

 these steels at ordinary temperature are somewhat less than 

 those found by other methods of determination : this discre- 

 pancy is probably due to the scaly oxide formed on the 

 surfaces of these wires, a phenomenon which was unavoidable 

 in our experiments ; but the metals which are not oxidizable 

 have the normal value of rigidity. 



The curves so far obtained can be generally stated as 

 follows : — They pass through observed points as well as 

 the melting-points of respective metals, so that they are 

 initially concave towards the axis of temperature, then pass 

 through inflexion points and become convex toward the 

 same axis, vanishing at the melting-points of the respective 

 metals. 



The logarithmic decrement of fusible metals increases 

 rapidly with the rise of temperature. As the melting-point 

 of metals is higher, the initial increase of logarithmic decre- 

 ment, when the temperature is gradually increased, is very 

 small, but its increase becomes very rapid from 150° C. 

 upward. Tn metals having very high melting-points the 

 logarithmic decrement diminishes at first, reaches a minimum, 

 and then increases with the rise of temperature. Hence 

 Tomlinson's view, that if we start with a sufficiently low 

 temperature the logarithmic decrement of all metals first 

 decreases, and, after passing through a minimum, increases 

 by the rise of temperature, seems to be correct. 



In ferro-magnetic substances this general rule of the 

 change is disturbed by the presence of magnetic transform- 

 ation. During heating this transformation affects the 

 logarithmic decrement by reducing its value. 



4. Coefficient of Viscosity. 



It is well known that the damping of the torsional oscillation 



