306 



SCIENCE. 



[N. S. Vol. IX. No. 218. 



in the hands of a civilian, and civilian 

 methods have been applied in the adminis- 

 tration. At the present time it has been 

 continuously under the Treasury for a 

 period of sixty- two years. Although statis- 

 tics do not always give an adequate concep- 

 tion of the work to which they are sup- 

 posed to bear testimony, a general idea of 

 the activity displayed may be had from the 

 following statement of work done : 



350,000 square miles (906,500 sq. kilo.) of triaugu- 

 lation, embracing 

 15,000 stations for horizontal measures, and de- 

 termining 

 28,500 geographical positions at which 

 1,000 astronomical coordinates have been ob- 

 served. 



38,500 square miles (99,710 sq. kilo.) of topog- 

 raphy, embracing 



11,600 miles (18,670 kilometers) of general coast 



line and more than 

 100,000 miles (160,900 kilometers) of shore line 

 (rivers, etc.), also including 



51,000 miles (82,080 kilometers) of roadways. 



545,000 miles (877,100 kilometers) of sounding, 



covering 

 164,000 square miles (424,800 sq. kilo) of area, 



besides 

 93,000 miles (149,700 kilometers) of deep sea 



sounding, in which 

 14,000 bottom specimens were obtained. 



4,600 original topographic and hydrographic 

 sheets, from which 

 1,300,000 charts have been made and distributed ; 

 30,000 original volumes of observations, including 

 magnetic records from 

 1,100 stations. 



BASE LINES. 



Two hundred and three base lines have 

 been measured, of whichnineteen,on account 

 of their accuracy, length and geodetic con- 

 nection, are classed as primary. The average 

 length of these is 9,892 meters. The prob- 

 able error, which includes both that of 

 measurement and the comparison with the 

 stajidard, is 22.2 millimeters, or about 

 l/^^OOO of the length stated. Speaking 

 of the three types of apparatus used in the 



Survey, and referring now to errors of 

 measurement purely, it may be said that 

 with the different forms of metallic bars, 

 compensating and otherwise, the error is 

 one-millionth part of the length measured. 

 With the tape line the accuracy may be in- 

 creased to 1/2,000,000, while with a rod in 

 melting ice 1/5,000,000 is easily attainable. 

 In the first form the contacts are material ; 

 in the last, optical ; with the tape they are 

 linear. The cost is greatest for the rod in 

 melting ice, and least with metallic bars. 



Attention may here be called to a new 

 form of base apparatus named the Duplex 

 and designed by Assistant William Eim- 

 beck. It consists of two bars, brass and 

 steel, five meters in length, so arranged 

 that the measure may be made with each 

 component separately and simultaneously. 

 It may also be employed as a Borda scale, 

 or the temperature may be directly ob- 

 served. Some unique features, which need 

 not here be described, are employed iu its 

 manipulation. The Salt Lake base, meas- 

 ured in 1896, gave results with either com- 

 ponent having a probable error of less than 

 1/5,000,000 part of the measured length. 



TRIANGULATION" AND ARCS. 



The shore line of the United States, ex- 

 clusive of Alaska, is 5,452 miles (8,774 kilo- 

 meters). This has been covered by tri- 

 angulation, with the exception of a few 

 hundred miles on the northwest coast. An 

 oblique arc of 22° has been measured from 

 the northeast bouudarj' in Maine, to the 

 southwest limit of Alabama, on the Gulf of 

 Mexico, and an arc of 49° on the 39th par- 

 allel of latitude has been completed, from 

 the Atlantic to the Pacific. All of the New 

 England States, a large part of the Middle 

 ones, and considerable areas in the South 

 and West, have been covered with triangu- 

 lation. Adjacent regions have had careful 

 reconnaissance. The work in this direction 

 has been executed on a large and accurate 



