THE FOUCAULT PENDULUM 



445 



titions in the Cathedrals of Cologne, Amiens and Rheims, in the tower of 

 St. Jacques and the Conservatoire des Arts et Metiers at Paris, on Bunker 

 Hill Monument, and in the dome of our Rotunda by Prof. Courtenay, 

 though this was never reported. A letter written in 1851 and recently 

 brought to Ught, tells us that Professor George Tucker, once of this Uni- 

 versity, tried the experiment from a back window of his residence in 

 Philadelphia, and with success. I was told by one of his successors here, 

 Prof. N. K. Davis, who at the very time was a student in the same city, 

 that he was led to repeat the experiment, and obtained a striking deviation 



of the vibration-plane. Upon studying the result closely, Mr. Davis, 

 with characteristic sagacity was led to doubt its being the genuine Foucault 

 disturbance and so stopped his attempts although urged to repeat the 

 swings before the Philadelphia Academy, by some enthusiasts who seemed 

 to think that any deviation would do. 



Similar severe scrutiny resulted in the rejection of other trials. In- 

 deed nothing is easier than to get deviations of the vibration-plane of any 

 pendulum. It is hard to avoid elliptical motion of the bob. Any lateral 

 disturbance of the point of suspension, or lack of care in starting the swings. 



