422 Mr. H. Pealing on an Anomalous 



Some of the specimens of strip 0*00.43 cm. thick showed 

 quite as much variation of the torsional rigidity as those only 

 0*0010 cm. thick, but as a rale this was not so, and the 

 thicker specimens showed less variation. Phosphor-bronze 

 wire 6 mm. diameter showed no variation in the torsional 

 rigidity, although loads of up to 4 kilograms were tried. 



Diminution of the Discrepancy with Time. 



The graphs obtained were the same no matter in what 

 order the readings were taken, and the values obtained were 

 not appreciably different when the readings were repeated i£ 

 that was done so at once ; but the values obtained when a 

 strip was newly set up differed considerably from those 

 obtained a few days later, the strip having been under a 

 tension of 25 grains weight in the interval. This alteration 

 in rigidity continues for a few days. This is shown in fig. 2, 

 curves I., II,, & III. It must be concluded that the strips when 

 under tension gradually alter in structure, and that this 

 alteration is of a permanent nature and makes the strip have 

 a greater restoring couple when supporting small loads than 

 formerly. Other strips which were tried did not show such 

 a pronounced initial difference between the torsion for a 

 slight and for a heavy load, and also showed a much smaller 

 alteration with time, but the alterations that were observed 

 were always in the same direction, and were most pronounced 

 for the small loads. 



Influence of Amplitude on the Effect. 



A few preliminary experiments showed that the time of 

 swing altered very little if at all with increase of amplitude. 

 The rod which was held in the stirrup was displaced from its 

 ^equilibrium position about 180°, and the time of the first 

 20 swings was found to be very little different from the time 

 of any 20 swings subsequent to these, which were of course 

 necessarily of much smaller amplitude. In all the obser- 

 vations mentioned in this communication an initial amplitude 

 of 180° was made ; but whenever this was not done it was 

 never found that the time of swing was appreciably different. 



Influence of Vamping on the Effect, 



The damping of the oscillation in all these experiments, 

 although it wa? not very large, was still very noticeable. 

 The damping was due to two causes, the resistance of the air 

 and the viscosity of the strip. The first may be dismissed 

 from consideration, as it can have only a negligible effect on 

 the period of the rod, but the second is certain to have 



