Oct. 1 8, 1883] 



NATURE 



595 



the steam from a little copper,/ placed at some distance 

 from it. 



The arrangements we have just briefly described enable 

 a difference of readings between the air thermometer 

 and the mercurial thermometer to be determined to nearly 

 the hundredth of a degree. 



From the descriptive summary thus given it will be 

 seen how important is the new and remarkable inter- 

 national establishment now really established in the neigh- 

 bourhood of Paris. It remains to add a word regarding 

 the benefits which the labours of this institution are 

 calculated to yield and the phases they have actually 

 assumed. 



The signing of the Metre Convention of 1875 will 

 necessarily be followed in the near future by the adoption 

 of the metric system on the part of all the nations of the 

 civilised world. The universal introduction of a uniform 



system of weights and measures, by establishing a new 

 bond between people and people, and by promoting inter- 

 national relations, will undoubtedly prove a powerful 

 factor in the interests of civilisation. This, however, is 

 not the only, nor even the principal, interest of this 

 international work. It was not necessary, it may be 

 properly asserted, for the purposes of commerce and 

 industry, to create a collection of such complex and 

 perfect instruments and machines. More than anything 

 else the interest of the labours of the bureau is scientific. 

 Science will more and more cease to rest content with close 

 approximations ; in all possible branches it craves rigorous 

 exactitude, it aims at precision. The International Bureau 

 will furnish science not only with standards of measure- 

 ment exactly controlled and verified, but also with a 

 great number of physical constants determined with the 

 greatest care and under conditions as perfect as poss ble. 



Fig. 4. — Apparatus for Measurement of Temperature and Barometric Pressun 



Among all the sciences the one which will reap the 

 greatest benefit from the new institution is geodesy. In ; 

 fact one of the greatest drawbacks to an exact knowledge 

 of the figure of our globe is just the uncertainty still prevail- 

 ing in regard to the relative values of the measures which, 

 having been employed for the measurement of the different 

 bases, have served as points of departure for triangulations 

 executed on various points of the earth's crust. The 

 minute study of these measures, centred henceforth in the 

 laboratories of Breteuil, will assuredly cause the trouble- 

 some discrepancies to vanish, and will offer a surer basis 

 for the labours of geodesists. As much may be said 

 for the study of the variations of gravity by means of the 

 pendulum. The International Commission have decided 

 on taking as the point of departure for the new metric 

 units the standards already existing, that is, the metre and 

 the kilogramme of the archives of France in their actual 

 state. This decision ought to receive unqualified approval. 

 While rendering full homage to the great and valuable 



idea, formed at the end of last century, that the basis of 

 universal measurements must besought in the dimensions 

 of the globe occupied by the human race, it ought also to 

 be understood that for the present day the pith of the 

 matter does not centre in the metre being a few microns 

 (millionths of a millimetre) longer or shorter. The great 

 point is that the whole world possess the same metre, and 

 that the copies distributed be all perfectly equal to the 

 standard, or rather rigorously determined in relation to 

 that standard. To demand over and above that the 

 length of the metre tally exactly with its theoretic defi- 

 nition would assuredly be demanding that the metre be 

 subjected to periodical retouchings and modifications in 

 order to make it keep pace with the progress of science, 

 which would be the very worst of inconveniences for a 

 fundamental unit. 



This point settled, the next thing was to make an inter- 

 national metre and kilogramme, — copies, viz. as exact as 

 possible of the metre and the kilogramme of the archives, 



