FISCHER: LENGTH STANDARDS AND MEASUREMENTS 157 



and using the bars. It is probable that this form of apparatus 

 would have been extensively used and have superseded all other 

 base bars but for the introduction of tapes. In 1900 and 1901 

 a party of the Survey measured nine base lines along the 98th 

 meridian, using these bars and fifty- and one hundred-meter 

 steel tapes. The tape measures agreed so closely with the 

 bar results that the officials felt justified in discarding bars 

 altogether for base measuring, and in substituting tapes. Mr. 

 A. L. Baldwin who had charge of this campaign of base measure- 

 ments described his season's operations in an address before this 

 Society. An elaborate report on the work is contained in the 

 1901 report of the Survey.^ 



But the problem of an entirely satisfactory base measuring 

 apparatus was not solved until the discovery of the nickel- 

 steel alloy called "invar" with very small temperature coeffi- 

 cients. Tapes made of this alloy used during the day and sub- 

 ject to the usual temperature variations, when exposed to the 

 sun's rays, gave better results than the steel tapes used at nighty 

 and at a lower cost. All primary bases of the Coast and Geo- 

 detic Survey are now measured with invar tapes, and in each of 

 the other countries conducting geodetic surveys the base appara- 

 tus, which is nearly always in the form of tapes or wires, is made 

 of invar. A paper was read before this Society by Mr. O. B, 

 French in which he gave the results of various tests of invar 

 tapes made at the Bureau of Standards and in the field during 

 actual measurements. 



What, may we inquire, were the industries doing for stand- 

 ards while they were in the hands of the geodesists, and before 

 the establishment of the National Standardizing Laboratories? 

 It would be impossible for one to cover the whole field in the 

 time at my disposal nor do I think the development in the 

 different countries was sufficiently different to require this. 



The need of accurate and reproducible standards was no- 

 where felt sooner in the industries than in the United States, 



* Other publications of the Survey which give the results of recent measure- 

 ments of bases are Appendix 5, Report for 1907; Appendix 4, Report for 1910 

 and Special Publication No. 19. 



