154 FISCHER: LENGTH STANDARDS AND MEASUREMENTS 



It had been decided as early as 1873 that the new standards 

 should be made of an alloy of 90 per cent platinum and 10 per 

 cent iridium, and that they should be line standards. Alto- 

 gether 31 meters and 40 kilograms were constructed. By 1889 

 the entire work was completed and in September of that year a 

 , general conference was held at Paris, and by it the work of the 

 international committee was approved. 



The meter and kilogram which agreed most closely with the 

 meter and kilogram of the Archives were declared to be the 

 international meter and the international kilogram. These two 

 standards, with certain other meters and kilograms, were de- 

 posited in a vault under one of the buildings of the international 

 bureau, where they are only accessible when three independent 

 officials with different keys are present. The other standards 

 were distributed by lot to the various governments contributing 

 to the support of the international bureau. Those falling to the 

 United States were meters Nos. 21 and 27, and the latter of these 

 two standards, which was accepted as the National Prototype, 

 superseded our earlier standards. 



Practically all that has been said heretofore has had reference 

 to standards rather than to measurements made with them. In 

 deciding upon what measurements to select for discussion it 

 appeared to me, that none were more interesting than the measure- 

 ment of base lines. Perhaps my interest in them is due to the 

 fact that I was a witness to very radical changes in the method 

 of making them. When I entered the Coast and Geodetic 

 Survey over 30 years ago my first task was to assist in a very minor 

 capacity in determining the lengths of two base measuring bars 

 of a new design which will be found described in appendix No. 7 

 of the Report of the Survey for 1882. 



These bars were supposed to be compensated for temperature, 

 the metals being two steel bars connected to the opposite ends 

 of a zinc bar in such a manner that the expansion of the two 

 different metals would compensate one another. They were 

 end standards and the method of using them in the field was the 

 well known one of supporting the bars on tripods and placing 

 them end to end. The standard with which they were com- 



