300 Messrs. Ayrton and Perry on the Determination 



centimetre. The weight of the wire was 11*6 grammes, and 

 its length 934*99 centimetres at 0° C. Its moment of inertia 

 was therefore 3*3803 x 10 6 (gramme, centimetre), and the dis- 

 tance of its centre of gravity from the axis of rotation 467*49 

 centimetres. The weight of the brass ball was 2352*2 grammes, 

 its moment of inertia about the axis of rotation 2*0744 x 10 9 , 

 and the distance of its centre of gravity 939*09 centimetres at 

 0° C. Of~the whole system, then, the weight was 2371*6 

 grammes, the moment of inertia about the axis of rotation 

 2*0778 x 10 9 (gramme, centimetre), and the distance of its 

 centre of gravity 2*2144 x 10 6 . Consequently 



_/tt\ 2 2*0778 xlO 9 

 9 ~~\t) 2*2144 xlO 6 ' 



and 



or 



or 



£=3*0748 seconds; 



<7=979*58 centimetres per second per second in air, 



^=979*74 centimetres per second per second in vacuo 

 for the Imperial College of Engineering, Japan — 



a result agreeing extremely closely with the number 979*7 

 obtained above from Clairault's formula. 



In beginning this series of observations we expected to find 

 g to be greater than what Clairault's formula gives it. Our 

 reason was this : — Clairault's formula assumes a circular 

 equator ; Capt. Clarke has found that the equator is ellip- 

 tical, one extremity of its major axis being in 15° 34' E. 

 longitude ; and therefore Tokio is in longitude nearer a minor 

 axis than a major one. We find, however, a reason why g 

 satisfies so well Clairault's formula, in spite of this excentricity 

 of the equator. The greatest depression of the earth's surface 

 is only a few hundred miles to the east of Japan; and probably 

 the diminution in g produced by this cause just counter- 

 balances the increase of g produced by ellipticity of the 

 equator. As for local perturbations, it is to be remarked that 

 Tokio is situated on a very large plane, there being no hills 

 of any magnitude within eighty miles. We think that the 



feodesy of Japan is of special interest on account of the great 

 'acific depression, and on account of the very gradual slope 

 of the earth's surface from Japan to China, which causes Japan 

 to be a sort of ridge. 



Probably the best method of determining the value of g 



