31^ 



attained. As we shall have to refer to these papers more than once 

 we shall quote by volume and page from "Bosscha's Verspreide 

 geschriften" (B.'s collected papers) published in three volumes. 



The importance of a comparison of the Dutch metres with the 

 International jdatinum-iridium metre kept in Paris was, however, not 

 lost sight of by the Commission. It was probably by their request, 

 that in the protocol drawn up of the handing over of the two 

 metres bj^ the Frencii Section of the international Metre-Commission 

 to the Dutch delegates Bosscha and Oudemans it was specially stated : 

 Cette remise est faite sous la réserve du droit qu'aura le Gouver- 

 nement des Pays Bas de faire etfectuer les comparaisons entre ces 

 metres et le prototype du Bureau international des poids et mesures 

 pour la determination de leurs equations a i'égard de ce mètre. 



However, not only did the Dutch Commission leave open the 

 possibility of obtaining a direct comparison with the international 

 metre later on, but also l)y making determinations at Paris of the 

 differences between the Dulch metres and metres which are in their 

 turn coiuiected to the International metre, they took care, that the 

 I'elation between the lengths of our metres and the International 

 metre can be calculated. 



Although all the observations which are required for these calcu- 

 lations are fully communicated in Bosscha's papers and only very 

 simple calculations are suflicient to obtain the relation in question, 

 the results have not been published either by Bosscha himself or 

 as far as I know by anybody else ; and as they are needed in order 

 to express the length of our base-line in international metres, I shall 

 here shortly communicate them. 



The relation to the International metre is obtained not only through 

 the metre des Archives A (see further down), but also through the 

 two Metres /^ and 20, both of the second alloy of Matthky, of 

 which jM is also made; in addition use is made of the two metres 

 23 and 27 both of the first alloy (metal du conservatoire). 



For the reduction of the difference of length of 23 and /^ the 

 difference of the coefficients of expansion of these two metres is 

 required, and I shall therefore try to derive its most probable value 

 from the results communicated by Bosscha. 



In the first place we ma}^ conclude from Bosscha's calculations, 

 that the metres of the second alloy have all got the same coefficient 

 of expansion (Vol. Ill, p. 74 — 76). The equality of the coellicients 

 of exi)ansion of the metres 1, 3, 12, and 13 of the first alloy is 

 also demonstrated (Vol. Ill p. 77). According to Fizeau's measure- 

 ments llie coefficients of expansion of the metres 19, 27, and 23 of 



