544 



NA TUBE 



\Oct. 31, 1872 



INTERNATIONAL METRIC COMMISSION 



TH K following methodical statement of the resolutions come to 

 by the International Commission on Weights and Measures 

 st its recent meeting at Paris was presented to the Frencli 

 Academy of Sciences by M. Tresca, one of the secretaries of 

 the Commission. 



I. In n-fa-eme to the Md-c 



1. As a starting-point for carrying into effect an international 

 measure, tlie Commission takes the metre of the Archives, in its 

 present condition. 



2. The Commission declares that, considering the actual con- 

 dition of the platina measure of the Archives, it thinks tlie 

 marked or line metre {milre h tmils) may be deduced from it 

 with certainty. Nevertheless, tlii; opinion of the Commission 

 requires to be confirmed by the different processes of comparison 

 which can be employed in this investigation. 



3. The proportion (ijiiatioii) of the International Metre will 

 be deduced from the present length of the metre in the Archives, 

 determined according to all the comparisons which have been 

 made by means of the processes which the International Metric 

 Commission will be in a condition to employ. 



4. While deciding tliat the new International Metre ought to be a 

 line-metre (iiutir a trails), of which every country will receive an 

 identical copy made at the same time as the universal prototype, 

 tlie Commission will feel bound afterwards to construct a certain 

 number of standards marked by projections {f/alons d bonis) for 

 those countries which desire them ; and the proportions of such 

 metres to the new prototype d trails, will also be determined 

 under the care of the International Commission. 



5. The International Metre will have the length of the melre 

 at zero (centigrade). 



6. There will be employed for the manufacture of the metres 

 an alloy composed of 90 parts of platina and 10 of iridium, with 

 a margin (iiiu- tolc-ranci-) of 2 to the 100, more or less. 



7. In manufacturing the measures, the ingot must be formed 

 by a single casting by means of the processes used in the working 

 of the known metals. The number and form of these measures 

 will be determined by the International Commission. 



S. These measures will be annealed for many days, at the 

 higliest temperature— notwitlistanding that they are never likely 

 tobe subjected to anything but the most feeble strains— before 

 taking them to be compared with the standard instruments. 



9. The bars of platina alloy upon which the line-metres are 

 to be traced, will have a length of 102 centimetres, and their 

 transverse section will be represented by the model described in 

 a note of M. Tresca. 



to. The bars intended for the construction of the projection 

 metre measures (it Ivtds), will have a similar transverse section, 

 but symmetrical in the vertical direction, conformably to the 

 special figure which represents it ; the nobs or projections [bonis) 

 will then be wrought with a spherical surface of one metre 

 radius. 



1 1. During all the operations which the standard metres must 

 undergo, they will be supported on the two rollers {rouleaux) 

 indicated by General Baron de Wrede ; but, for their preserva- 

 tion, they will be placed in a suitable case. 



12. Each of the International Metres ought to be accompanied 

 by two mercurial thermometers, isolated, and carefully compared 

 with an air-thermometer ; it is deemed necessary that these 

 thermometers should be verified from time to time by means of 

 the air-thermometer. 



13. The method of M. Fizeau will be employed to deter- 

 mine the dilatation of the platina alloy used in the construction 

 of the metres. 



14; The prototypes will be submitted to the processes by 

 means of which the coefficients of the absolute dilatation of the 

 complete metres can be best determined. These measures will 

 be separately made, at five different temperatures at least, 

 between zero and 40" centigrade. 



15. The comparison of the prototypes with each other ought 

 to be made at, at least, three temperatures comprised between 

 these same limits. 



16. The Commission decides that two apparatus be con- 

 structed, the one with a longitudinal movement for tracing 

 these metres, the other with a transverse movement for Dieir 

 comparison. 



17. The comparisons will be made by immersing new standards 

 in a liquid and in air ; but the standard of the Archives must not 

 be immersed in any liquid before the end of the operations, 



iS. The tracing of the line or traced metres (d traits), and their 

 first comparison with the metre of the Archives, will be for the first 

 efTected by means of M. l'"izeau's process. 



19. For the determination of the proportions of the various 

 standards, there will be employed moreover all the means of 

 comparison already known and approved, according to circum- 

 stances, either by actually bringing tlie different forms into con- 

 tact, or by the method of Messrs. Airy and .Struve, or by that of 

 MM. Stamkart and Steinheil. 



20. The relations between the Archive metre and the new 

 International traced metre, as well as the relations between the 

 other traced standards and the International Metre, will be deter- 

 mined by comparing the results of all these observations. 



21. Operations will be performed, on the other hand, by setting 

 out from the International Metre for the construction of the 

 standards with projections (I'la/o/is a bouts), which may be asked 

 for by various states. 



II. /« rcfcren:e to tJu' Kilogramme 



22. Considering that the simple relation estalilished by the 

 authors of the metric system between unity of weight and unity 

 of volume is represented by the actual kilogramme in a manner 

 sufficiently exact for the ordinary uses of industry, and even of 

 science ; considering also that the exact sciences liave no real 

 need of a simple numerical relation, but only of a determination 

 as exact as possible of that relation ; and considering the difficul- 

 ties which would result from a change of the existing unity of 

 metric weight, it is decided that the international kilogramme will 

 be derived from the kilogramme of the Archives in its present 

 condition. 



23. The International Kilogramme ought to be decided by 

 weighing in a vacuum. 



24. The material of the International Kilogramme will be the 

 same as that of the International Metre, viz. : an alloy of pla- 

 tinum and iridium, as stated in No. 6. 



25. The material of the kilogramme will be founded and cast 

 in a single cylinder, which will afterwards be subjected to furnace 

 heat and mechanical operations, such as will give to its whole 

 mass the necessary homogeneity. 



26. The form of the International Kilogramme will be the same 

 as that of the kilogramme of the Archives, viz., a cylinder whose 

 depth is equal to its diameter, and whose corners may be easily 

 rounded. 



27. The determination of the weight of the cubic decimetre oi 

 water ought to be made under the direction of the International 

 Commission. 



28. The balances which will be used for weighing ought to be, 

 not only those which may be placed for the present at the disposal 

 of the Executive Committee by institutions and men of science 

 who possess them, but also a new balance constructed according 

 to conditions of the greatest exactness. 



29. The volumes of all kilogrammes will be determined by the 

 hydrostatic method ; but the kilogramme of the Archives will 

 neither be placed in water nor in a vacuum before the end of the 

 operations. 



30. To determine the weight of the new kilogramme, in com- 

 parison with that of the Archives, in a vacuum, two auxiliary 

 kilogrammes will be made use of, as nearly as possible of the 

 same \\'eight and the same volume as that of the Archives, 

 according to the method indicated by M. Stas. Each of the new 

 kilogrammes ought also to be compared in air with the kilo- 

 gramme of the Archives. 



31. When the International Kilogramme is constructed, all 

 others will be compared with it, in air and in vacuum, for the 

 determination of their proportions. 



32. For this 'purpose is employed the method of alteration 

 and that of substitution, with a counterpoise of the same material. 



33. The corrections for losses of weight in air will be effected 

 by means of the most precise and least disputed data of science, 

 ill. In reference to the carrying out of the Commission'' s Decision 



34. The making of tire new prototypes of the metre and the 

 kilogramme, the tracing of the metres, the comparison of the new 

 prototypes with those of the Arcliives, as well as the construction 

 of the auxiliary apparatus necessary to these operations, are 

 entrusted to the care of the French section, with the concurrence 

 of the Permanent Committee, provided in the following article. 



35. The Commission has chosen from its members a Permanent 

 Committee, which will do duty till the next meeting of the Com- 

 mission, with the folio-wing organisation and powers : — (a.) The 

 Permanent Committee will be composed of twelve members, 

 belonging to different countries. Five of these members 



