158 



THE NATIONAL GEOGRAPHIC MAGAZINE 



weight ; but now the scope of weights 

 and measures is immensely broadened, 

 for many new commodities are in the 

 market which were formerly unknown, 

 such as electric current, light, heat, re- 

 frigeration, and services of other kinds. 

 The term "measures" now includes the 

 measurement of energy, velocity, power, 

 illumination, and electricity. 



The standardization of these new and 

 often intricate measures requires very 

 elaborate equipment and a high standard 

 of scientific attainment in the worker. 



ti-ie; sort of pe;oplk who nised the 



BURKAU 



Perhaps the best idea of the far- 

 reaching work of the Bureau may be 

 gained by glancing over the mail arriv- 

 ing any morning at the Director's office. 

 Here are letters from iron-founders, 

 tanners, iron-pipe makers, textile engi- 

 neers, optical instrument makers, dyers, 

 photographers, universities, well-sinkers, 

 Chicago meat-packers, glass-makers, mu- 

 nicipalities, manufacturers of refriger- 

 ating plants, contractors in concrete, 

 railroad officials, lamp-makers, boiler- 

 makers, chemical manufacturers, rail- 

 road commissioners, glass-blowers, pa- 

 per-makers, officials of international sci- 

 entific commissions, makers of fine- 

 mesh cloth for sieves, engineering firms, 

 dry-goods houses, officials of almost 

 every department of the federal govern- 

 ment, makers of oleomargarine, carpets, 

 water-meters, gas-meters, and watches, 

 and, finally, officials of foreign govern- 

 ments. 



Thus the Bureau does for the manu- 

 facturer something of what the Depart- 

 ment of Agriculture is doing for the 

 farmer. 



THE STANDARDS OF AL,h MEASURES OE 

 WEIGHT AND LENGTH 



Perhaps the division of weights and 

 measures has a greater interest for the 

 layman than any other division of the 

 Bureau. Here are preserved the funda- 

 mental standards on which all measures 

 of weight and length depend. These are 

 kept under double glass cases in a fire- 

 proof safety vault and are never used 

 except to check the copies that have been 

 adopted as working standards. 



The unit of length is the meter, which 

 is defined as the distance, at the tem- 

 perature of melting ice, between two fine 

 lines ruled on a bar of platinum-iridium, 

 which is kept at the International Bureau 

 of Weights and Measures at Breteuil, 

 near Paris, France. Accurate copies of 

 this bar have been made and distributed 

 to the various governments of the world; 

 that preserved at the Bureau is No. 27. 



In shape it resembles the letter H, 

 with the uprights bent slightly outward. 

 The scale marked upon it is so fine as to 

 be almost invisible to the naked eye. 

 When this prototype is to be compared 

 with any other meter, both bars are 

 placed side by side in a receptacle, which 

 is then placed in an oil bath in a trough- 

 like comparator, which is kept at an even 

 temperature. Microscopes are mounted, 

 on an invar-steel bar, and with the most 

 delicate micrometer screws are adjusted 

 to the prototype ; the standard to be com- 

 pared is then brought beneath them and 

 the difl^erence, if any, is recorded. Ob- 

 servations are made to the i/254,oooth 

 of an inch (see page 155). 



Measures of considerable length — as, 

 for example, the invar tapes used in the 

 United States Coast and Geodetic and 

 the Geological Survey — which are tested 

 by the Bureau before and after each ex- 

 pedition, are compared in a long tunnel 

 in the basement of the main building. 

 This tunnel is kept at an even tempera- 

 ture by means of a series of hot and cold 

 pipes, and a five-meter bar, packed in ice 

 and mounted on a movable carriage, to- 

 gether with microscopes mounted on in- 

 dependent piers at fixed intervals, is used 

 to test any bar or tape up to 50 meters in 

 length. On the other side of the tunnel 

 is an iron bar 164 feet long, in which 

 platinum-iridium plugs are inserted at 

 intervals. This also is used for testing 

 tapes and similar measures requiring less 

 exact determination. 



The standard of mass, which most 

 people call weight, is the kilogram (see 

 page 154), also of platinum-iridium, and 

 comes, like the meter, from Krance. The 

 Bureau possesses the two copies of the 

 original kilogram numbered 4 and 20. 

 From this prototype all other weights, 

 such as the pounds avoirdupois and 

 Troy, are derived. 



