534 Mr. A. Griffiths on an Apparatus for the Determination 



Now 



V-i /I 01.0 c, 



hence 



md 



similarly 



v ± = _ (*—*V2\ 



f, 1— a&n 



l-a&H 12*a(0 s -0,) 



— TL : 



r2L = 12^(1-^)^2-^) . 

 A ' T(2- a 6^T£>) ? 



r 1 L_12a(l-^ 2 )(^-^) 



k T(2-a0 1 -t0 2 ) 



The correcting factor equals 



2 



= 1 + g v 2 T + V ^ -, approx. 



As an example, if (0 2 -0,) = O°'l C, T = 0\L, and « = 0'00015, 

 the correcting factor equals r00000007. 



When T is a small fraction of unity, as in general will be the 

 case, the correcting factor equals 



!+ Tp —9 approx. 



It may be noted that, approximately, 



12k*(0 2 -0 2 ) 



As an example, let & = 3x 10" 6 , «=0'00015, {0 2 -0 l ) = O'l, 

 T = 0'1, L = 4cm. 

 Then 



i; 2 = l'35x 10~ 9 cm. per second, 



~0*04 cm. per year. 



