March 3, 1899.] 



SCIENCE. 



309 



They are checked by zenith distances from 

 the Chesapeake Bay to the Ohio River, and 

 supplemented by the same method from 

 Denver to the Pacific coast, where the spirit 

 levels are not yet completed. 



Permanent magnetic observations have 

 been in operation at Philadelphia, Key 

 West, Madison, Los Angeles, and each one 

 has furnished records for five consecutive 

 years; vcith one exception a self-registering 

 apparatus has been continuously and ex- 

 clusively employed in each locality. These 

 data added to records from 1,100 widely 

 ■distant points, many of which are secular 

 variation stations, furnish precious ma- 

 -terial for the study of the earth's magnet- 

 ism. The work of the Survey in the inves- 

 tigation of the force of gravity has been 

 ■carried on both within and without the 

 limits of the United States. Twenty-eight 

 foreign stations have been occupied, includ- 

 ing points in Europe, Asia, Africa, Aus- 

 tralia and many islands in both the At- 

 lantic and Pacific. New light on the 

 •subject of volcanic formation, as well as on 

 the constitution of the earth's crust, has 

 come from this work. Fifty nine-stations 

 have been observed at home, including a 

 line across the continent. Half-second 

 pendulums are now exclusively employed, 

 and the determinations are purely differen- 

 tial. The period of oscillation is usually 

 known to within a few millionths of a sec- 

 ond. 



In the field of Physical Hydrography 

 most comprehensive studies have been 

 made. 



The exploration'of the Gulf Stream, in- 

 cluding a study of its density, temperature 

 and currents, the geology of the sea bottom, 

 the establishment of cotidal lines, the de- 

 termination of the ocean depth from earth- 

 quake waves and other specialties in the 

 domain of hydrography, have been made a 

 part of the regular work. The hydrog- 

 .raphy of the coast, to the head of tide- 



water, has been developed side by side with 

 the triangulation and topography. 



The practical results of the Survey are 

 shown in the publication of the annual re- 

 ports, the issue of charts, notice to mari- 

 ners (corrected monthly), coast pilots for 

 Atlantic, Pacific and Alaskan waters, tide 

 tables (now extended to foreign ports) 

 and various miscellaneous publications in 

 special lines of research. 



PRESENT AND FUTURE OPERATIONS. 



A resurvey of Chesapeake Bay, the meas- 

 urement of an arc through the United States 

 on the 98th meridian, and the development 

 of Alaskan geography, are among the proj- 

 ects of Dr. Pritchett, the present superin- 

 tendent of the organization. All these 

 have been carried on during the last two 

 years. The line of transcontinental precise 

 levels is being pushed westward with all 

 available means. Primary triangulation on 

 the Pacific coast has been resumed, and will 

 soon be completed from San Francisco to 

 the Mexican boundary. Hydrographic sur- 

 veys are in progress along the Atlantic sea- 

 board, on the Pacific, and at the mouth of 

 the Yukon in Alaska. Numerous topo- 

 graphic, astronomic and magnetic parties, 

 are employed in the interior. 



An extension of the great arcs, of the 

 United States into Mexico and the British 

 possessions has been proposed by Dr. 

 Pritchett, and diplomatic representations 

 between the interested governments look- 

 ing towards concerted action in the near 

 future have already been made. This will 

 give to North America an additional me- 

 ridian arc of about 55° and an oblique one 

 of 33°. Together with existing arcs, the 

 proposed material will practically exhaust 

 our contribution to the determination of the 

 earth's figure. 



In the ordinary prosecution of the field 

 work since 1895 about fifty parties have 

 been employed during the course of each 



