Dr Searle, A bifilar method of measuring the rigidity of wires 69 



m 



By (15), T^D = l (-1023 + -0910) = -09665, 



and by (16), nD - -0752 + -0644 - (-0224 + -0185) = -09870. 

 Mean value of irD = 0-0977. 



Then, by (17) C= ""^ ^ = 0-03210. 



By (18), P= - i (-1023 - -0910) = - 0-0028, 



and by (19). Q=l (-0482 + -0405 - -0977) = - 0-0045. 



In the table, the column "sin/3 calcd." gives sin ^3 as calculated by (14), 

 using the values of ttD, P and Q just found; there is fan agreement between the 

 calculated and observed values of sin ,3. 



The total load M was 417-6 + 4999 = 5416-6 grm. 



Taking E = 10^^ dyne cm.--, we have r- {2TrE/Mg)^ = 1-35 cm., and hence, 

 by (4), I' = 47-30 - 1-35 = 45-95 cm. 



Then, by (7), 



n = ?^!.MC = - ^'^J^~^l^, X 5416-6 x 0-03210 

 TvrH' IT X 0-0352* x 45-95 



= 3-277 X 10" dyne cm 



-2 



A similar set of observations, m which ilf was 3417-lgrm., gave the following 



values of sin /3: 



•1510, -1123, -0743, -0361, -0000, - -0345, - -0735, - -1122, - -1540. 



Mean value of ivD = 0-1532. Hence C = 0-05127. 



Also I' = 47-30 - 1-70 = 45-60 cm. 



Then 



981 X 32 X 47-30 



TT X 003.52* X 45-60 



X 3417-1 X 005127 = 3-326 x 10" dyne cm." 



An independent determination of n was made by attaching a bar, of moment 

 of inertia K = 4-766 x 10* grm. cm.^, to each of the two wires in turn; the mean 

 periodic time of the torsional vibrations was T = 10-55 sec. Hence 



87r X 4-766 x 10* X 47-30 „ „. _ ,_., , .3 



10-55^ X 0-0352* = ^'^^^ ^ ^^ ^^^^ ^"^- " 



