CD. WALCOTT. 



THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



♦♦♦ 



Art. I. — Measurement of the Peruvian Arc; by 

 E. D. Preston.* 



Oxe hundred and fifty years have passed since Bouguer was 

 making his observations in the measurement of the Peruvian 

 arc. The geodetic science of to-day is so much occupied with 

 the slight deviations of the surface of the earth from a strictly 

 elliptical figure, that it is hard to realize that even in the last 

 century it was an unsettled question whether the equatorial or 

 polar axis was the longer. 



A clock, having been carried from Paris to the equator, was 

 found to lose two minutes each day. This fact was supposed 

 to strengthen Newton's theory that the earth was an oblate 

 spheroid. On the other hand, Cassini's surveys in France at 

 the beginning of the last century, indicated a prolate spheroid. 

 It was to reconcile these two determinations that the French 

 Academy undertook the measurements of Meridional arcs ; one 

 on a frozen river in Lapland, the other above the clouds in 

 Peru. 



Parenthetically, it should be stated, however, that the Peru- 

 vian arc so called, is not in Peru as defined by the geography 



* Read before the American Association for the Advancement of Science, 

 Toronto meeting, August, 1889. Published by permission of the Superintendent 

 of the U. S. Coast and Geodetic Survey. 



Am. Jour. Scl— Third Series, Vol. XXXIX, No. 229.— Jan\, 1890. 

 1 



