714 



SCIENCE. 



[N. S. Vol. XXIV. No. 623. 



past three years in those countries; (2) the 

 presentation of special papers bearing upon 

 improvements in instruments, methods of 

 observation and methods of computation; 

 (3) the transaction of the business of the 

 association itself at the conference, in con- 

 nection with the continuous operation of 

 the central bureau maintained at Potsdam 

 and in connection with the tield work be- 

 ing done by the association as an organ- 

 ization; and (4) the social features of the 

 meeting. 



Through this and similar conferences a 

 close and effective cooperation of many men 

 of many nations, acting as an association, 

 is secured in a certain few lines of research. 

 Of these the greatest now being carried for- 

 ward is an investigation of the variation 

 of latitude. 



Aside from this cooperation, all the ac- 

 tivities of the conference served to make 

 it a clearing house for ideas, a place where 

 each may learn what ideas, old or new, are 

 being acted upon in geodetic work in other 

 countries than his own. In this process 

 the social functions play an important part 

 in bringing men together and helping them 

 really to understand each other. 



The association, as such, does not fix the 

 methods of observation or computation in 

 any country. It controls only the methods 

 used in its own central bureau and in the 

 field work paid for from the association 

 funds. But, by virtue of the active inter- 

 change of ideas which takes place at the 

 conferences, the association undoubtedly 

 exerts a strong influence in making the 

 methods used in various countries much 

 more uniform and progressive than they 

 otherwise would be. 



The reports of progress within the past 

 three years which were submitted show 

 that the rates of progress in accumulating 

 new results are very different in different 

 countries, depending upon a great variety 

 of conditions. Each country brought 



some contribution and the total represents 

 a rapid increase in the mass of geodetic 

 facts available for future use. It would 

 be tiresome to summarize these reports here 

 and the summaries would be of little value. 

 Three items are, however, of special inter- 

 est. Progress has been made within the 

 last three years in the observations and 

 computations connected with an arc in 

 Spitzbergen and in connection with the 

 remeasurement of the classical Peruvian 

 arc, extended. Progress has also been 

 made in South Africa on the measurement 

 of an arc which is expected, ultimately, to 

 extend from the Cape of Good Hope to the 

 northern part of Russia, a total length of 

 104°. 



Let us turn now to the special papers 

 bearing upon improvements in instruments, 

 methods of observation and methods of 

 computation. 



Th. Albrecht, of Germany, presented a 

 report on a thorough investigation made 

 at and near Potsdam, of the applicability 

 of wireless telegraphy to the accurate de- 

 termination of differences of longitude. 

 The transmission time was found to be ex- 

 tremely small and sensibly independent of 

 the particular receiver used and of the in- 

 tensity of the sending. 



Though not a delegate to the conference, 

 Ch. Ed. Guillaume, of the International 

 Bureau of Weights and Measures, by 

 special invitation occupied the greater part 

 of one session in presenting the results of 

 the many tests of the Invar (nickel-steel) 

 wires made at the International Bureau, 

 describing the apparatus devised there for 

 the rapid measurement of bases with In- 

 var wires, and in giving a general state- 

 ment in regard to the use of this appa- 

 ratus in the measurement of a base extend- 

 ing the entire length of the recently com- 

 pleted Simplon tunnel. The extensive in- 

 vestigations of the International Bureau 



