Ixxvi GENERAL SUMMARY OF SCIENTIFIC AND 



been effected by any thing but floating ice coming from the 

 northeast, and that the great agent in denudation was the 

 arctic current passing over the region when submerged. 



GEOGRAPHY. 



In Geodesy, the steady activity of innumerable workers 

 prevents our noting more than a comparatively few events, 

 such as the publication by the French government of the first 

 sheets of the new Topographical Map, on a scale of ^-^, 

 with contour lines for each one hundred meters. These are 

 the first results of the survey ordered in 1870. 



The field mark on the central European arc of longitude, 

 extending from Valentia, Ireland, to Orsk, in Asia, having 

 been completed in 1872, it is estimated that the computations 

 will occupy still another year. The office work is conduct- 

 ed under the supervision of the Russian geodesists, through 

 whose dominions two thirds of the triangulation extends. 

 Accurate surveys of Hayti are also in progress. 



The principal new geodetic work that is at present con- 

 templated is in connection with the determination of the po- 

 sitions of that part of the globe covered by the stations for 

 the observation of the transit of Venus. 



The question of determinations of altitude by means of ac- 

 curate leveling has been treated of in several interesting: es- 

 says, both theoretical and practical, concerning the errors 

 incident to such operations. We note especially the deter- 

 mination by Baeyer of the errors in the German survey that 

 depend upon local deviations of the plumb-line. Still more 

 numerous have been the essays on the use of the barometer 

 for the determination of altitude ; of which we can make 

 special mention only of the very clear and practical work of 

 J. D. Whitney and W. H. Pettee, published by the Geolog- 

 ical Survey of California. 



A complete remeasurement of the area of Russia has been 

 made by the use of the Amsler Planometer, as applied to 

 the improved charts of the present day. 



We have not heretofore announced the completion by the 

 Coast Survey of two new base-lines one extending from 

 Farmington, Maine, to Nantucket, and the other from the 

 head of Chesapeake Bay to Ocracoke. A base-line of 48,100 

 feet has been measured by Major Powell in the Canon region 



