ACOUSTICS AND GRAVITATION. 



79 



The frame carrying the wire in the above experiment was therefore removed 

 and an electric current (10 amperes) passed through the wire from end to end, 

 till it showed the blue oxide coat virtually equivalent to tempering in lead. 

 The adjustments of the wire in the frame were not otherwise disturbed. Hence 

 on putting the frame back in the interferometer, the fringes were found at 

 once. Observed in the zero position (no stress), the wire showed no displace- 

 ment of fringes in the lapse of time, due to viscosity. 



The observations (table 2, series i) were now made for the viscous yield- 

 ing of the wire with a gram weight on one scale-pan. 



The wire is thus about 2.5 times more rigid than in the hard-drawn 

 state. In fact, if r= AN/ AN', the ratio of yielding caet. par., in the two 

 cases, the results obtained by graphic interpolation show 



Time 10 20 40 70 120 minutes 

 r= 0.42 0.41 0.39 0.41 0.46 



Variations at the beginning are attributable to fluctuations of temper- 

 ature. It must be noticed, however, that the change of stress is here from 

 zero and thus but half the change (reversal) occurring in the preceding 

 experiment. The effective increase of viscosity is thus not so large as was 

 looked for. Twisting the wire in the opposed direction by shifting the 

 grams to the opposed scale-pan, the viscosity, therefore, diminished con- 

 siderably, as was expected. The second twist, moreover, is always character- 

 ized by maximum yield. The readings (beginning about 4 minutes after 

 twisting) are given in table 2, series 2. The rigidity gained by the tempered 

 wire as compared with the original wire is about 30 per cent, not as much 

 as was hoped. 



TABLE 3. Viscous deformation of hard-drawn steel wire, tempered blue. Diam. 0.05 cm., 

 length 35 cm .(one-half effective). Double twist 50, due to counterpoise of i gram. 



* After twisting^back and forth about 100 times. 



