Decembeb 7, 1906.] 



SCIENCE. 



715 



show that the changes in length to which 

 the Invar wires are subject are so small, 

 and that the Invar wires have such phys- 

 ical properties, that they are suitable for 

 the measurement of primary bases. The 

 experience in the Simplon tunnel confirms 

 this conclusion. The base apparatus there 

 used is elaborate in comparison with that 

 now in use in the United States for the 

 measurement of primary bases with steel 

 and Invar tapes. It also differs radically 

 from the Coast and Geodetic Survey (U. 

 S.) apparatus in having the entire meas- 

 urement carried forward on movable tri- 

 pods, just , as measurements with base bars 

 are made, instead of being carried forward 

 on stakes driven in the ground, as are the 

 tape measurements in the United States. 

 The Simplon tunnel base was 20 kilometers 

 long. The tunnel was placed entirely at 

 the disposition of the measuring party for 

 five consecutive days, no trains being run 

 during that time. The measurement was 

 made continuously in each direction 

 through the tunnel, the party working in 

 shifts of eight hours, day and night. The 

 forward measurement was made in 59 hours. 

 The remeasurement was made, after a day 

 of rest, in 27 hours. The total number of 

 persons employed on the measurement at 

 any one time was 28. Seventy-seven dif- 

 ferent persons in all were involved in the 

 measurement. This performance and its 

 results leave no doubt that the necessary 

 accuracy can be secured more quickly and 

 conveniently with Invar wires than with 

 any bar apparatus. Any one who will 

 carefully compare this work, in all respects, 

 with what has been accomplished with steel 

 and nickel-steel tapes in the United States, 

 on primary base work, will also be convinced 

 that all the advantages claimed for wires 

 may also be claimed for tapes, and that the 

 use of tapes, rather than of wires, and of 

 stakes, rather than of tripods, makes the 



measurement much more rapid, economical 

 and convenient, and that the tapes are 

 more reliable, as to length, than the wires. 



Baron Eotvos, of the University of 

 Budapest, occupied the greater part of one 

 session in presenting a discussion of the 

 results secured by him with certain torsion 

 balances of special design. A similar pre- 

 sentation may be found in Wiedemann's 

 Annalen, 1896, and another in the report 

 of the Congres International de Physique, 

 Paris, 1900. He evidently aroused much 

 interest. The conference visited his labo- 

 ratory in a body to see the apparatus. He 

 derives from the observations the first dif- 

 ferentials of gravity with respect to dis- 

 tance measured along the three rectangular 

 axes at the point of observation. From 

 these observed quantities may be derived 

 various other quantities, such as, for ex- 

 ample, the radii of curvature of the geoid 

 at the point of observation. The claipis 

 made as to the simplicity of the manipula- 

 tion of the apparatus, the accuracy of the 

 results, and the certainty with which the 

 positions of the excesses and defects of 

 mass within the earth may be determined 

 by such observations, are astonishing. If 

 the validity of these claims is established by 

 future investigations, these torsion balances 

 will become very important as being the 

 most powerful means available for deter- 

 mining the distribution of density within 

 the earth. 



Dr. 0. Hecker exhibited the very inter- 

 esting apparatus which has been used by 

 him, under the direction of the association, 

 for determining the value of gravity at 

 sea. He presented the results of recent 

 observations made with this apparatus on 

 the Pacific on two voyages between Sidney, 

 Australia, and San Francisco, and between 

 San Francisco and Yokohama. The at- 

 mospheric pressure is determined in terms 

 of millimeters of mercury by a mercurial 



