UNIVERSITY OF VIRGINIA PUBLICATIONS 



BULLETIN OF THE PHILOSOPHICAL SOCIETY 



SCIENTIFIC SECTION 



Vol. I, No. 21, pp. 443-456 August, 1914 



THE FOUCAULT PENDULUM, MADE A USEFUL LECTURE- 

 ROOM APPLIANCE 



BY 



FRANCIS H. SMITH 



The diurnal motion of the earth is best evinced and measured, both as 

 to its great fundamental statement and the minute departures from this, 

 by the apparent daily motion of the fixed stars caused by it. No mere 

 terrestrial apparatus will probably ever release the physicist from de- 

 pendence on the astronomical observatory as regards the exact value of 

 this rotation. 



Yet philosophers have for a long time believed that so great a fact 

 ought to reveal itself by purely terrestrial evidence and many in recent 

 centuries have sought for it. 



Ne-R-ton, in a letter to Hooke, pointed out that a body falling freely 

 ought by the rotation of the earth to be made to deviate to the east of the 

 plmnb line. Hooke replied that it should deviate to the south of east. 

 Laplace undertook a mathematical analysis of the falling motion and 

 agreed with Hooke. Gauss followed and deduced from his treatment 

 that the deviation would be to the north of east. Other mathematicians 

 found no deviation at all from Newton's purely eastward deflection. After 

 a long silence the mathematical problem has recently been taken up by 

 Dr. R. S. Woodward who has pushed the analysis a step farther, by taking 

 account of small quantities neglected by Laplace and Gauss, with the 

 interesting result that a heavy body falUng in vacuo in our hemisphere, 

 should deviate to the north of east. 



The experiments on the deviation of freely falling bodies have been few 

 and unsatisfactory. They require a great vertical distance, a very ac- 

 curate determination of the vertical itself, and heretofore, the use of a 

 mine shaft, with all the atmospheric troubles which this involves. These 



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