778 Mr. J. C. Buckley on the 



Experiments on the distribution o£ the active deposit of 

 thorium are now in progress and will soon be published. 



In conclusion I wish to express my gratitude to Prof. E. 

 M. Wellisch for suggesting this problem and for his continual 

 interest and advice throughout the course of the investiga- 

 tion. I am also indebted to Prof. Boltwood for his helpful 

 suggestions. 



Sloane Physical Laboratory, 



Yale University, New Haven, Conn. 

 May 18, 1914. 



LXXXIV. The Bifilar Property of Twisted Strips. By J. C. 

 Buckley, M.Sc, Demonstrator in Physics in the University 

 of Liverpool *. 



AN apparently anomalous variation in the rigidity of 

 phosphor-bronze strips has been observed by Prof. 

 Wilberforce and A. Campbell f, and was investigated by 

 Pealing J. 



When a strip carrying an inertia bar is twisted its period 

 of vibration depends upon the load. It is well known that 

 in a bifilar suspension the period depends upon the load, 

 hence it has been suggested that there is a bifilar action 

 which accounts for the behaviour of the strips. 



Pealing, however, contrary to Campbell, found that the 

 anomaly disappeared slowly with time if a strip was sub- 

 jected to continued tension, and disappeared completely in 

 the case of a strip which had been annealed. 



The object of this paper is to determine more exactly the 

 amount of variation to be theoretically expected and experi- 

 mentally obtained due to bifilar action. 



Theory. 



Consider a strip to be composed of a number of conse- 

 cutive fibres, parallel to the length of the strip, of breadth dr, 

 r being the distance of the fibre from the neutral line (fig. 1). 



Suppose one end of the strip fixed, while the other end, 

 which carries the inertia bar, is twisted through the angle 0. 



n 



If 1 = length of the strip, then j =angle of twist per unit 

 length. 



* Communicated by Prof. L. R. Wilberforce. 

 t Proc. Phys. Soc. April 1913, p. 203. 

 J Phil. Ma*. March 1913. 



