268 



SCIENCE. 



[Vol. I., No. 10. 



tions of local authorities, or the enterprise 

 of private map-publishers : ' ' The radical dif- 

 flcult}' with our modern survej'S lies not in 

 want of capacit}-, integrity, or ambition among 

 the local survej-ors, but in the want of a sj's- 

 tem of lines measured with absolute precision, 

 and permanently marked, which can be made 

 a base of all surveys, and can furnish checks 

 at short distances, and keep errors within cer- 

 tain well-defined limits." 



A trigonometrical survej- of this nature, 

 whenever completed, will be used in a great 

 varietj' of waj's, entirelj' independent of &\iy 

 topographical mapping that maj' be founded 

 upon it. In pursuance of this policj', the sur- 

 vey has been confined to trigonometrical work. 

 The triangulation is based on that of the 

 U. S. coast and geodetic survej', which had 

 l)een extended across Massachusetts to the 

 Hudson ; certain stations on the Hudson River 

 series of coast-survey triangles having been 

 connected both with the New England and 

 Fire Island bases. Comparison of results from 

 these diflferent lines of measurement shows that 

 the positions of points overlooking the Hudson 

 Eiver vallej' are known with great exactness, 

 and ma}' therefore be used as starting-points 

 for most accurate surveying. 



The lines of principal triangulation are be^ 

 ing pushed into the settled parts of the state 

 as rapidlj' as possible, in order to set tertiary 

 stations for use of local surveyors, wherever 

 propertj' is most valuable, and to save bound- 

 aries whose loss seems imminent. Principal 

 stations being once established, the subdivision 

 in smaller triangles, and determination of pub- 

 lic boundaries, can proceed at separate places 

 whenever demanded by the exigencies of spe- 

 cial regions, and can be done at the expense 

 of individuals, towns, and counties. 



The Hudson vallej' is alreadj' well supplied 

 with principal stations hy the U. S. coast sur- 

 vey. The state survej' has therefore planned 

 to lay out a series of principal triangles ex- 

 tending from Albanj' westward through the 

 central and western counties of the state ; and 

 another from the lower part of the Hudson, 

 through what is known as the southern tier of 



counties. The first of these, or the central 

 series of triangles, begins at the coast-survey 

 stations, Rafinesque and Helderberg ; the first 

 being north-west of Troj', and the latter west 

 of Albanj' on the Hudson River. The distance 

 between these points, which is the base of this 

 sj-stem of triangles, is about 36,966 metres. 

 The triangulation beginning at the Hudson 

 runs westward, si^anning the valley of the Mo- 

 hawk River, and the vallej's which continue this 

 great depression westward across New York. 

 Along the shore of Lake Ontario, from Oswego 

 to Buifalo, the U. S. lake survey has measured 

 a small but accurate chain of triangles, a part 

 of their main chain along the lakes. With 

 this lake-survey triangulation, the scheme of 

 the state survej' was connected south of Oswe- 

 go ; the distance between the lake-survej' sta- 

 tions. Victory and Clyde, being the joining 

 line, and, in fact, forming a base from which 

 work was begun on the western part of the 

 state-survey chain, before connection was made 

 with the Hudson River section. 



The measurement of the angles of the larger 

 triangles is done with 12-inch horizontal cir- 

 cles divided b}^ Troughton and Simms of Lon- 

 don. One of them was, however, mounted hy 

 Fauth and Co. of Washington. The Fauth 

 theodolite has three reading microscopes di- 

 vided to seconds, and a telescope of 23 inches 

 focal length with object-glass of 2^ inches 

 diameter. The Troughton and Simms the- 

 odolite has two reading microscopes divided 

 to seconds. The angles of the smaller sec- 

 ondar}-, and of the tertiarj' triangles, are meas- 

 ured with 8-inch Troughton and Simms circles 

 with two reading microscopes divided to sec- 

 onds. These instruments have also vertical 

 circles divided and read in the same waj- as 

 the horizontal. 



A complete sj'stem of trigonometrical level- 

 ling is carried on in connection with the sec- 

 ondary and tertiarj' triangulation, the zenith 

 distances being observed with the 8-inch cir- 

 cles. Measurement of the horizontal angles 

 of each class are repeated until the probable 

 errors are within the limits prescribed hy the 

 U. S. coast survey and the British ordnance 



