18 C. Barns — Viscosity of Steel, etc. 



words relatively large variations of elasticity are superimposed 

 upon and obscure the nature of the viscous detorsion during 

 the interval of transition from high to low temperature, or from 

 low to high temperature. It is because of the mixed char- 

 acter of the retrograde movement that I refrain from using the 

 data for the construction of the temperature relations of the 

 rigidity of steel. If a device for cooling with sufficient rapidity 

 to annul the viscous movement, be applied, then the present 

 method may be used at once for investigating the effect of 

 temperature on rigidity. This I have occasion to show in my 

 next paper. 



Sudden and gradual deformation. — In the experiments for T= 

 100° the rate of twist r=6° was uniformly applied. The results 

 were then approximately reduced to r=3° by merely halving 

 the values of <p. Figure 4 shows that the same strain, r= 6°, 

 applied for T=190°, is too large for convenient measurement 

 by Gauss' method. On applying r=3° directly, the complete 

 series of results of figure 3 is obtained. Comparing the loci of 

 figure 3 and figure 4, it appears clearly that <p increases very 

 much more rapidly than r. Moreover, if the rate of increase 

 of r be 2, the rate of increase of <p is certainly as much as 3 in 

 case of An. 190°, and even more than 10 in case of soft (An. 

 1000°). It follows therefore very probably that the viscous 

 relations of soft steel to hard steel vary enormously and may 

 even change sign as the stress producing viscous motion passes 

 from low to high values (cf. p. 3). This is an important de- 

 duction. For rates of twist less than r=3° for the diameter 

 2o = O082 cm , steel is less viscous, and as regards viscosity much 

 more susceptible to the influence of temperature, in proportion 

 as it is harder. For rates of twist greater than r=6° steel is 

 less viscous and more susceptible to the influence of tempera- 

 ture in proportion as it is softer. The complete coordination of 

 these facts, in other words the full expression of the viscosity 

 of steel as a function of hardness for all degrees of temperature 

 T and all values of stress r, will be the key for the explanation 

 of the mechanical behavior of steel and its important bearing 

 on magnetic, electrical and other properties of the metal. To 

 elucidate these remarks I will complete the description of the 

 apparatus with which the present results were obtained. 



In the apparatus, figure 1, page 2, suppose the lower (cold) 

 wire to be in connection with clock-work, in such a way that 

 it may be twisted uniformly, at any given velocity, variable at 

 pleasure. Suppose the method of adjusting the index to be 

 such as is suitable for the measurement of angles of any magni- 

 tude. If the clock be set in motion from r=0, the strain will 

 increase at some determinate arbitrary rate. For a given value 

 of T, therefore, a family of curves may be obtained in which 



