6 C. Bar us — Viscosity of Steel and 



safely be used to interpret the electrical result : in both 

 experiments we observe mechanical strains disappearing under 

 like conditions. 



The table contains another important result : by comparing 

 the second part of the table with the first, it appears that the 

 effect of temperature in decreasing the viscosity of steel is 

 greater in proportion as steel is harder. For where the twist 

 r is stored between two glass-hard wires it is found to have 

 almost completely vanished after annealing ; but where the 

 same twist is stored between two soft wires less than one-third 

 of it has vanished after annealing. The curious inference that 

 in so far as its viscous properties are concerned, steel is much 

 more susceptible to temperature when it is hard than when it 

 is soft, will be carefully discussed in the following pages by 

 aid of the apparatus already described. 



Torsional viscosity and temperature. — The data of the follow- 

 ing thirteen tables give a clear description of the viscosity of 

 steel for temperatures between 0° and 400°, and for all degrees 

 of hardness. These data are readily intelligible. T denotes 

 the temperature of the hot part, T' the temperature of the cold 

 part of the wires in the apparatus, p. 2. The distance be- 

 tween mirror and scale was 360 cm throughout. L, b, k, a, have 

 the signification already given, being the total length of wires, 

 the distance of mirror above their lower end, the length of their 

 cold and of their hot parts, respectively, in centimeters. The 

 tempers of the rods (diameter 2p) are expressed by the tem- 

 perature at which the originally glass-hard rod was annealed. 

 Soft rods are annealed at red heat. The tabular arrangement 

 contains the date and the time (h ) in hours and fractions of an 

 hour, of each of the angular detorsions <p, in radians. <p has 

 been defined, p. 1. It denotes the angular viscous motion 

 between two right sections whose distance apart is the unit of 

 length, when the temperature of the included wire is T° and 

 the original rate of twist r for the given diameter 2/?. Identi- 

 cal signs of z and <p refer to angular motions in the same sense, 

 and since z and <p agree for the cold rod this is invariably of 

 greater viscosity. 



