Rigidity of Phosphor Bronze in Strips. 207 



to place the strip carefully between two square rods of brass 

 whose dimensions were 12 in. x -J in. x J in. The whole was 

 then heated to a suitable temperature and kept hot for about 

 an hour. But even in this case slight ci inkles developed in 

 the strips. The easiest explanation of this is as follows. 

 The strips during the process of manufacture are overstrained, 

 particularly on the surface. These overstrains are of such 

 a nature that they make the strip perfectly uniform in 

 thickness and free from kinks. During the process of an- 

 nealing, the function of the outer layer in jacketing the 

 inner layers is removed, and the strip takes on its natural 

 shape, which is by no means smooth and regular. If this 

 view is correct, it is a very doubtful advantage to anneal the 

 strips, for while that removes one disadvantage it introduces 

 another. By the exercise of care the last disadvantage could 

 be very considerably minimised. All the strips on which 

 experiments were made, when annealed showed a very small 

 variation in the torsional rigidity under different tensions. 

 This was particularly well brought out in the case of the 

 second strip. The values obtained are shown in the table. 

 For loads up to thirty grams the rigidity is practically 

 constant. The value for a load of forty-five grams showed a 

 slight increase. In the case of the other strips the increase 

 in rigidity for the heavy loads was a little more pronounced, 

 especially in the case of the fourth one. This increase I 

 consider to be due to two reasons : 



(1) Imperfect annealing. 



(2) The straightening out of the annealed strips by the 



heavy loads. 



The first was the more usual cause of the increase 

 as further annealing reduced the increase. In all cases the 

 increase was very small compared to the increase obtained 

 when using unannealed strips. 



The experimental evidence is such that we are entitled t«> 

 conclude that if there is a bifilar effect in the >trips. if is 

 excessively small and completely masked bv other effects. 

 On the other hand, the removal of the effect by annealing 

 can only be easily explained by the fact that during the 

 process of manufacture the strips were considerably over- 

 strained, and seems to justify the conclusion that it is an 

 anomalous variation in the rigidity of the phosphor bronze, 

 and not an apparently anomalous one. 



Liverpool University. 



