418 Mr. H. E. Wimperis on 



this plan was adopted and the results are given : very little 

 variation was found. 



The next step is to clamp one rod horizontally and allow 

 the other to hang down below, the under one is then slightly 

 rotated — so twisting the wire — and released. The period of this 

 vibration is also found, and called t%. 



Here again a re-determination is made by turning the appa- 

 ratus upside down ; this corrects variations in the moment of 

 inertia of the rods. 



The constants of the apparatus were carefully determined 

 thus : — 



Bar A. Bar B. 



Weight = 2-932 lb. =2-936 lb. 



Length =18'50 inches. =18*50 inches. 



Breadths 0-75G inch. = 0755 inch. 

 (Mean of four measurements.) 



Depth = 0-763 inch. = 0'763 inch. 

 (Mean of four measurements.) 



M °W ; °a f }=K = 0-2167 =-2170 



Mean value of K= 0-2169. 

 The formulae given by Mr. Searle are: — 



'i 



W 



^- = p( 1 + a ) and °" = 2N ' 



Where a = -^r Tr = correction for mass o£ wire, 

 bOK 



E = Young's modulus, 



N= modulus of rigidity, 



K = moment of inertia of bars, 



I = length of wire, 



a = radius of wire, 



o-=Poisson's ratio, 



m = mass of wire. 



Fig. 2 shows the method of suspension in the first 

 part of the experiment. 



CD is a part elevation of one rod suspended from a cord 

 at H. E is the ^-inch screw which screws into a hole in the 

 top of the rod and grips the wire at G. The under part of 



