The Coast Survey Level 



With the beginning of this Century, the U. S. C. & G. S. dis- 

 carded the wye-construction in favor of a precision dumpy type, of 

 which our Engineers' Precise Level is a simplified modification. To 

 overcome the effects of temperature the telescope and the 

 outer tubularencasement werecast in nickel-steel and nickel- 

 iron and wherever the vast experience of the geodecists 

 of this department dictated radical and scientific departures 

 from conventionalities, they were adopted with con- 

 spicuous success. It is said America leads the world in 

 the accuracy, rapidity and economy of precise leveling. 

 Outside of the powerful telescope and the method of 

 observing the bubble, by prismatic reflection, at the instant 

 of observation, the chambered level vial is the domi- 

 nating feature of its construction. 



A view of the chambered vial is given in Fig. 17. 

 There is a glass partition between the larger and smaller 

 chambers with a tunnel connection in the under side. The 

 fluid is sulphuric ether, which finds its equilibrium quickly 

 but is more susceptible to temperature changes than 

 alcohol. When, in very hot weather, the air bulb shrinks 

 within the normal lines, there is made an exchange of fluid 

 andair through the orifice by a little clever manipulation. 

 These vials are sensitive to one or two seconds of arc 

 and uniformly ground. 



We have manufactured this instrument to official 

 specification since its inception, but the question of precis- 

 ion leveling is rather too involved for exposition here. 

 For the student who desires to pursue the topic we append 

 a list of references : 



U. S. C. & G. S. Report, 1900, Apx. 6, p. 521 



Trans. A. S. C. E., Vol. XLV, 1901, pp. 127-175 



U. S. C. & G. S. Report, 1902, Apx. 4; ibid 1903, p. 200 



J. F. Hayford in Eng. News July 2, 1903 



E. M. Douglas " " " May 17, 1906 



C. H. Lee " Sept. 17, 1908 



H. W. Maynard " Cornell "Civil Engineer" May '09 



andNov.'lO 



H. C. Mitchell " Eng. News, Mar. 23, 1911, p. 356 

 C. M. Cade " Eng. & Cont. Nov. 29, 1911, p. 591 



Prof. W. H. Burger, Trans. Ills. Soc. Eng. & Surv. 

 Fig. 17 Vol. 26, p. 141 



"Geodetic Surveying" Prof. E. L. Ingram 1911, p. 153-162 

 W. E. Jessup in "Wisconsin Engineer" Mar. 1913 

 W. N. Showalter in National Geographic Magazine, June 1914 

 Rausch & Lomb Metro III Catalog, p. 116 etc. 



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