Chap. IV. PARRY'S FIRST VOYAGE. 121 



that of No. 8, " An account of the experiments to., 

 determine the acceleration of the pendulum in dif- 

 ferent latitudes," which would appear to have been 

 the joint labour of Parry and Sabine. " The acci- 

 dental discovery," it is said, "that a pendulum, on 

 being removed from Paris to the neighbourhood 

 of the equator, increased its time of vibration, 

 gave the first step to our present knowledge that 

 the polar axis of the globe is less than the equa- 

 torial, and that the force of gravity at the surface 

 of the earth increases progressively from the equator 

 towards the poles." In the present instance two 

 clocks were used in these experiments, being the 

 property of the Royal Society, and the same which 

 accompanied Captain Cook round the world ; and 

 the result is stated to be, that the mean daily accele- 

 ration of the two clocks was seventy-four thousand 

 seven hundred and thirty-four vibrations, which is 

 considered as the true acceleration of a pendulum 

 between the latitudes of 51° 31' 08" (London) and 

 74° 47' 14" (Melville Island) ; and the deduction, 

 which was obtained from the result of the accelera- 

 tion, between London and Melville Island gives the 

 diminution of gravity from the pole to the equator 

 to be ,0055258; and this decimal gives for the 

 ellipticity of the earth -^. 



But as Captain Sabine in the year 1821 (the next 

 following that of his arrival in England) embarked 

 on a most arduous undertaking to investigate the 



