206 Mr. H. Pealing on an Anomalous Variation of 



made before those with the larger tensions, or vice versa. 

 The figures in the column may therefore be considered to 

 represent with fair accuracy the rigidity of the strips as 

 they are before being experimented upon. The initial 

 behaviour of strips I. and II., it will be seen from the table, 

 is very similar, but that of II. is very remarkable indeed. 

 For small tensions the rigidity is fairly high, then we get a 

 sharp drop, and after that a more gradual fall until we reach 

 a tension of twenty-five grams weight. For greater tensions 

 than that Ave get a very sharp rise indeed. The behaviour 

 of strip III. is scarcely less remarkable. For small tensions 

 the rigidity is very low, arid as the tension is increased we 

 get a very sharp rise throughout the range of the experi- 

 ments. Entirely different from the behaviour of I., II., and 

 III. is that of strip IV. In that we get a low value of the 

 rigidity for small tensions, then a very sharp rise followed 

 by a sadden transition to a gradual rise to a high value. 

 In the third strip, the rigidity for a tension of about one 

 gram is only 027 of its value for a tension of twenty-five 

 grams weight and 0*143 of its value for a tension of forty- 

 five grams weight, a very extraordinary variation. 



Now phosphor-bronze strips are very largely used for 

 galvanometer suspensions and universally for moving-coil 

 galvanometers. No doubt when the galvano meters have 

 been working for some time, their behaviour will be regular. 

 It is, however, no less certain that when a new phosphor- 

 bronze suspension is fitted to a galvanometer, the re- 

 storing couple per unit angle of displacement will gradually 

 increase for the first few days. A second point of im- 

 portance is the figure of merit of a galvanometer that we 

 may expect to get when using phosphor-bronze suspensions 

 of given dimensions. The above results show that this 

 cannot be predicted with any certainty at all. Take for 

 example the restoring couple per unit angle of displacement 

 for tension of *91 grin. In strip III. it is less than one-third 

 of the value for strips I. and II., and only about one quarter 

 of the value for strip IV. This discrepancy is no less for 

 greater tension, as the values for a tension of twenty-five 

 o-rms. show. 



Effect of annealing the strips. 



It is not easy to anneal satisfactorily very thin strips. If 

 they are annealed while they are under no tension or pres- 

 sure of any sort, they are very liable to crinkle and develop 

 numerous kinks. The method I found most satisfactory was 



