76 abstracts: geodesy 



GEODESY. — Triangulation in California, Part II. C. R. Duvall 

 and A. L. Baldwin. App. No. 5, Rept. Coast and Geodetic 

 Survey for 1910. Pp. 173-429. 40 illus. 1911. 



The geographic positions on the United States Standard Datum, of 

 triangulation points between Monterey Bay and Trinidad Head, Cali- 

 fornia, are given with all available descriptions of stations, and 40 

 sketches, together with a complete index. 



The results of the primary, secondary and tertiary triangulation of 

 1906-07, executed principally to determine the effect of the earthquake 

 of 1906 on the old triangulation, are here published in full for the first 

 time. Along with the newly determined position of each of the 61 old 

 points is given the position resulting from observations made before the 

 earthquake. For a number of the old points it was possible to compute 

 separately the observations made before the earthquake of 1868, and for 

 these the three corresponding positions are placed together. A compari- 

 son of these positions and a discussion of the corresponding displacement 

 was published in Appendix No. 3, Coast and Geodetic Survey Report 

 for 1907. ("The Earth Movements in the California Earthquake of 

 1906," by J. F. Hayford and A. L. Baldwin.) C. R. D. 



GEODESY. — The measurement of the flexure of pendulum supports with 

 the interferometer. W. H. Burger. App. No. 6, Rept. Coast 

 and Geodetic Survey for 1910. Pp. 431-449. 5 figs. 1911. 



The interferometer was adopted by the Coast and Geodetic Survey 

 for determining the flexure of the pendulum supports in 1907. Pre- 

 liminary investigations were made by the author under the direction of 

 Mr. John F. Hayford with apparatus designed and constructed in the 

 instrument division of the Survey, under the immediate direction of 

 Mr. E. G. Fischer. The instrument and methods are here described and 

 illustrated in sufficient detail to enable one to use them successfully. 



This interferometer is a modified form of the one described in "Light 

 Waves and Their Uses," by A. A. Michelson. It has given excellent 

 results at more than sixty field stations in the United States during the 

 past three years and at the base station at the Sur ey office, while the 

 pendulums were being restandardized. This is believed to be the first 

 time that the flexure of the pendulum support has been determined satis- 

 factorily at field stations by this method. William Bowie. 



