202 



NATURE 



[Dec. 27, 1888 



THE INTERNATIONAL BUREAU OF 

 WEIGHTS AND MEASURES. 



ALTHOUGH the International Bureiu of Weights 

 and Measures has now been in existence for some 

 years, its work hardly appears to have been so generally 

 recognized as it ought to be. This may be owing partly 

 to the fact that the results of its labours are published in 

 volumes accessible only to a few ; and, partly, that the 

 researches of the Bureau, being in the direction of the 

 highest accuracy in physical measurement, are hardly 

 appreciated at first in the every-day work of ordinary 

 life. It may be well, therefore, to mention briefly the 

 contents of the five annual volumes of the Bureau which 

 have already been issued, before noticing the contents of 

 the sixth volume which lately reached us/' 



The first volume issued in 1881, under the immediate 

 direction of Dr. O. J. Broch, gives the results of the re- 

 searches made at the Bureau on the tension of aqueous 

 vapour ; on the fixed points of thermometers ; on the true 

 weight of a litre of air ; and on the specific gravity of 

 water. The second, third, and fourth volumes contain 

 papers on the dilatation of the standard metres ; on the 

 weighing of the standard kilogrammes ; and on the 

 dilatation of mercury. In the fifth volume may be found 

 an exhaustive consideration of the methods of verifying 

 subdivided linear measures ; of calibrating thermometers ; 

 and of correcting the progressive errors of micrometer 

 screws. This latter volume also contains thermometric 

 studies ; as well as studies of the theory of the balance 

 as applied to scientific weighings. 



The new volume (tome vi. pp. 620) contains three 

 papers, one by Dr. Rend Benoit, on the measurement of 

 dilatations by the method of M. Fizeau ; one on the com- 

 parison of mercurial thermometers with the air or hydrogen 

 thermometer, by Dr. P. Chappuis ; and a third paper on 

 practical formulae for the transformation of thermometric 

 coefficients, by Dr. A. E. Guillaume. 



M. Fizeau's method of determining the rate of expansion 

 of solid bodies by heat is well known {Atmales de Chiniie 

 et de Physique, 1864-66), but its application has hitherto 

 been difficult. Dr. Benoic has succeeded in removing 

 this difficulty, and by clear explanation and complete 

 formulas of reduction, has brought the use of this 

 dilatometer within the reach of the ordinary student. We 

 regret that our space prevents us giving an outline of 

 Dr. Benoit's methods and a sketch of the particular form 

 of dilatometer he uses ; the following, however, are the 

 coefficients of linear expansion for 1° C., from 0° to /°, as 

 ascertained by him during the past year : — 



Quartz — Direction parallel to the axis 



+ o 000007 1 107 

 + o 00000000856 



Direction perpendicular to axis j « ^ + VS^^{^, 



Beryl-Direction parallel to the axis... j « " ; l^^^^SS^^^ 



Direction perpendicular to axis { « = + l^^^\(,^ 

 -,, ,. f a =-h O •000008840 5 



Pl^'^'^"^ t)3 = + o-oooooooT89 



Platinum-iridium (Mr. Matthey's alloy, J a = i- 0000008615 



Type I.) / j8 = + o'oooooooo22i 



Gold coin, English sovereign and half- j o = + o '000014472 



sovereign ... ... J /3 = + o'oooooooo42i 



Steel cast by Messr.. Jessop and Sons... { « = + ^'.^^^^^^ 

 Brass and Bronze — 



Copper, 73751 



Zinc, 2418 ( /o = + o'ooooi782o 



Lead, 0-57 ( \ j8 = + 000000000584 



Tin, 1-52'' 



Copper, 8i-20N 



Zinc, 8-6jI /a = + 00000174^1 



Lead, 0-17 ( \ /8 = -I- 0-00000000618 



Tin, 9-87; 



I "Travaux et Mtfmoires du Bureau International des Poids et Mesure;," 

 tcmevi. (Paris : Gauthier-Villarje; Fils, 1888.) 



Phosphor Bronze (rich in phosphorus, hard)- 



Copper, 94 '6 \ 

 Tin, 47 



Phosphor, 07 J 



^ a- + o-ooooi6SSl 

 \ ;3 — + o •0000000061 8 



Dr. Chappuis states that since the study of the mercurial 

 thermometer has shown that this instrument is susceptible 

 of the greatest precision, there has been recognized a 

 necessity for stating its indications in a scale unique and 

 invariable. The choice of such a scale-presents serious 

 difficulties, for even in the best measurer of temperature — 

 as Regnault's air or gas-thermometer — practical measure- 

 ment is dependent on the limits of pressure between which 

 the measurement is made, and on the nature of the air or 

 gas used. The mechanical theory of heat has given a 

 new definition to temperature, independent of any suppo- 

 sition as to the regularity of the dilatation of bodies, and 

 furnishes therefore an absolute scale of temperature, 

 which, on the supposition that a perfect gas is used,, 

 should accord with the definition of temperature of the 

 gas thermometer. 



A rigorous verification and intercomparison have there- 

 fore been made by Dr. Chappuis of a gas-thermometer of 

 large capacity, with eight of Tonnelot's hard-glass standard 

 mercurial thermometers. He found that the scale-read- 

 ings of the mercurial thermometers differ as follows from 

 the scale-readings of air, hydrogen, and carbonic-acid 

 thermometers, the hydrogen-thermometer presenting the 

 greatest divergence : — 



o°'io7 C. at 40^ C. for hydrogen, 



o°-o97 ). 40'' M air, 



o°'049 ,, 35° ,, carbonic acid ; 



the difference in the march of the air and hydrogen 

 thermometers (7), and between the carbonic acid and 

 hydrogen thermometers (8), being represented by the 

 following formulas : — 



(7) T^s- Th = + 0-00542995(100 - T„)T,« 



-f- 1-4118126 X io-*(ioo"' - Tf«)T;„ 



- 1-322986 X io"®(ioo' - T„,)T,„. 



(8) Tco-2- Th = + 0-03591397(100 - T„,)T„, 



- 0-2310806 X io"-'^'ioo'^ - tL)T,„ 



- 0-510047 X io"''(ioo'' - t,;'!)t,„. 



Dr. Benoit has accordingly given the coefficients of ex- 

 pansion of the several bodies above referred to in terms of 

 mercurial thermometers made of crystal glass and of hard 

 glass respectively^ and of the hydrogen thermometer ; of 

 which the following is an instance : — 



L'near Coefficients of Dilatation for 1° C. 



By mercurial thermo- By mercuri4l therm i- 



meter made of crystal meter made of hard 



glass. glass. 



Gold (English Standard, \l) 



10-3(14473 + 4-27;-) ... io-''(i4497 + 4'03n ••• io-»(i457i + 3*i9^> 

 Platinum. 



io-»(8840-s + i-Sgt) ... io-''(8S55-hi-74/) ... 10-9(89014-1-21^^ 



We have recently called attention to the fact that the 

 work of the Comitd International des Poids et Mesures 

 is now approaching completion, so far as relates to the 

 delivery to each country of a verified copy of the metric 

 standards of measure and weight, the prototypes of which 

 are to be kept and maintained at the offices of the Bureau, 

 situated at the Pavilion de Breteuil. Sevres, near Paris; 

 and we are glad to see from the Proch-verbaux, also 

 recently issued by the Comite, that the Government of 

 this country have requested the Comitd to furnish the 

 Standards Department of the Board of Trade with exact 

 standards of the metre, and of the kilogramme, made in 

 platinum-iridium. 



