. 



THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Art. LIII. — The Study of the Earth's Figure by means of 

 the Pendulum ; by E. D. Preston. 



[Read before the Brooklyn Institute Feb. 26, 1891. Published by permission of 

 the Superintendent of the U. S. Coast and Geodetic Survey.] 



History. 



The idea of finding the size and shape of the earth is 

 probably one of the oldest in the history of science. Each 

 age has added to the knowledge of the age before it, and each 

 one has by its additions to existing data contributed to the 

 solution of the problem. From the time of Anaximander 600 

 years before Christ, when it was thought to be a cylinder with 

 a height equal to three times its diameter, down to the last 

 deductions of Clarke and Bessel which point to a spheroid with 

 three unequal axes, successive theories have been tested by 

 physical observations and corrected or modified by the facts 

 revealed by experience. It is not worth while to review all 

 the ancients thought or did on this subject. Such a study 

 would be interesting but not profitable for the present purpose. 

 The turning points or mile-stones on this highway of inquiry 

 may, however, be noted as showing how slow has been the 

 progress towards what we now believe to be the truth. The 

 cylindrical theory supposed the land and water to be on the 

 upper base. Seven successive generations accepted this idea 

 and when it was no longer considered tenable a cube was sub- 

 stituted for the cylinder. What a striking difference between 

 the intellectual activities of an age that required several 

 hundred years to pass from a cylinder to a cube, and was satis- 

 fied with this conclusion, and an age that in one-half the time 

 has determined the distance of the heavenly bodies and studied 



Am. Jour. Sci. — Third Series, Vol. XLI, No. 246. — June, 1891. 

 30 



