proceedings: philosophical society 557 



viN, Paul, Wenner, Swann, and C. A. Briggs, particularly with refer- 

 ence to correction on account of velocity of ship, pumping effects and 

 damping by decreasing diameter of capillary tube, correction due to 

 mean variation of instrument from vertical, and effect of non-uniformity 

 in ice packing. 



The 756th meeting was held on April 10, 1915, at the Cosmos Club, 

 President Eichelberger in the chair; 43 persons present. 



Mr. W. BoW'iE spoke on Geodetic work of the Coast and Geodetic 

 Survey. Reference was made to the measurement of arcs in Europe 

 in the 17th and 18th centuries, but for lack of time the history during 

 the ages before the 19th century was not dwelt upon. The problems 

 before the geodesist today were presented. Some of the earlier prob- 

 lems have been solved, the measurement of base lines l^eing one of 

 them. The nickel-steel (invar) tapes and wires now in general use 

 give results which are entirely satisfactory. The illustrations showed 

 the instruments used in the several branches of geodetic surveying and 

 the field methods were described. Every effort is made by the Survey 

 to reduce the unit costs of the work without decreasing the accuracy 

 of the results. The motor truck has been used successful^ as the 

 means of transportation for several seasons. Three of them will be used 

 by the primary triangulation party this year on the Utah-Idaho line. 

 Aside fr-om the scientific value of the geodetic surveys they have great 

 practical value, for they furnish the fundamental control for maps and 

 surveys made by government and private organizations. The paper 

 was discussed by Messrs. Winston, Curtis, Priestly, and L. A. 

 Fischer. 



Mr. R. B. Sosman then presented a paper by himself and Mr. J. C. 

 Hostetter entitled Note on the magnetic properties of iron dissolved in 

 ylatinum. This paper is printed in the Journal of the Washington 

 Academy of Sciences, 5: 293. 1915. The communication was dis- 

 cussed by Messrs. Burgess and Swann. 



Mr. H. E. Merwin then spoke on Chromatic reflection of covellite. 

 (Published in the Journal of the Washington Academy of Sciences, 5: 

 341-344. 1915.) The paper was discussed by Messrs. Humphreys, 

 Priestly, and C. A. Briggs. 



Mr. G. W. ViNAL then spoke on The solubility of metallic silver in 

 distilled water. The practice of nearly all observers with the silver 

 voltameter has been to continue the washing of the deposit until the 

 presence of silver nitrate can no longer be detected in the wash waters 

 by chemical tests, but many haye taken the further precaution of allow- 

 ing distilled water to stand on the deposit for a considerable period of 

 time. As a test on the completeness of the washing. Prof. G. A. Hulett 

 and the speaker compared the conductivity of the water before being 

 put in the cup with its conductivity after it had stood in the cup for 

 various periods of time. In every case the conductivity increased 

 with time. It was at first supposed that this increase was due to 

 entrapped silver nitrate gradually soaking out, as the silver in the 



