R. 8. Woodward — -Iced Bar Base Apparatus. 33 



The analysis gave : 



PbS0 4 74-76 



CaS0 4 19-64 



H 2 required to form gypsum.. 5'20 



99-60 



showing that these crystals had a considerable admixture of 

 gypsum. 



Cheni. Laboratory. Ill S. 10th St., 

 Philadelphia, Nov. 22d, 1892. 



Aet. IV. — Preliminary Account of the Iced Bar Base 

 Apparatus of the U. IS. Coast and Geodetic Survey /* by 

 R. S. Woodward. 



Historical Note. — The use of ice in thermometry to furnish 

 a standard temperature naturally suggests the availability of 

 ice to fix the temperature of a standard of length when used 

 in laboratory comparisons or in measuring base lines It does 

 not appear, however, that ice has been generally used even in 

 laboratory work with standards of length, f and I am not aware 

 that any attempt has been made hitherto to measure a base 

 with a bar whose temperature is controlled by means of melt- 

 ing ice. The feasibility of using such an apparatus in base 

 measurement has, nevertheless, been suggested and maintained 

 by several persons. One of the first, if not the first, to out- 

 line a scheme for such an apparatus is, I believe, Mr. E. S. 

 Wheeler, a former colleague on the U. S. Lake Survey. Mr. 

 Wheeler's plan is advocated by Professor T. W. Wright in his 

 treatise on the Adjustment of Observations.^ The late Cap- 

 tain C. O. Boutelle of the U. S. Coast and Geodetic Survey 

 also advocated the use of such apparatus. 



Soon after joining the U. S. Coast and Geodetic Survey in 

 July, 1890, 1 was requested by Dr. Mendenhall, Superin- 

 tendent, to devise means of testing in the most thorough way 



* Communicated by permission of the Superintendent of the Survey. The sub- 

 stance of this paper was presented before Section A of the American Association 

 for Advancement of Science, at the Rochester meeting, August, 1892. 



f From published accounts it would appear that the most extensive series of 

 laboratory comparisons of standards, wherein ice was used, are those of the IT. S. 

 Lake Survey, conducted under the superintendence of General C B Comstock, 

 Corps Engineers, U. S. A. In these comparisons ice was successfully used dur- 

 ing several years. See Professional Papers Corps Engineers, U. S. A , No. 24. 



\ D. Van Nostrand, New York, 1884. See also this Journal. Ill, vol. xxviii, 

 p. 479. 



Am. Jour. Soi. — Third Series, Vol. XLV, No. 265.— January. 1*93. 



