NEWTON S PKINCIPIA. 359 



found useful. The whole object of the investigation is 

 the determination of x. 



This mode of viewing the resistance to the motion of a 

 pendulum, was a great improvement. But Bessel was not 

 the first discoverer, though he was the first who called the 

 attention of the public to it. The chevalier De Buat had 

 treated of this very property of the pendulum in his Prin- 

 cipes tfHydraulique published in 1786, fifty years before. 

 &quot;And it is not a little remarkable that these important 

 and conclusive experiments of De Buat, which were made 

 by the order and at the expense of the French Govern 

 ment, which were examined at the request of the Minister 

 of War by the Royal Academy of Sciences at Paris, 

 and by them favourably reported on, which were first 

 published in the year 1786 and excited so much interest 

 that they led to the subject for the prize essay proposed 

 by the Academy in the following year, should have been 

 so completely lost sight of and forgotten that no one 

 should have had the least remembrance of the additional 

 correction for the pendulum pointed out by M. cle Bruat, 

 and until the rediscovery of this principle by Bessel no one 

 should have thought of verifying the suspicion of Xewton, 

 that such an effect was probable.&quot; Baily on the Correction 

 of a Pendulum, Phil. Trans. 1832. 



A variety of experiments have lately been made to de 

 termine the resistance experienced by the pendulum as it 

 makes its small oscillations in the resisting medium. One 

 obvious method is to swing a pendulum in air and vacuo, 

 and note the number of oscillations made in any given 

 time. Recurring to our value of X, it is easy to see that if 

 N be the number of oscillations in vacuo, and N&quot; the num 

 ber in air in any given time, that 



N&quot; - N 



k /i 2 + r 2 + y g *x //* + 



V /- y g ~V ~~T 



/IL+L! 



V ~T~ 



A A 4 



