311 



series of observations is Ihc mean of' llic values : 0.420 (T), 0.428 (liy, 

 0.434(111) and 0.40J (V) tiieretbre: 



m— :t 0..^421 



As the measnrenient of each portion of tiie ineasnring bar was 

 obtained for each observer b3- taking the mean of 8 series of obser- 

 vations, the mean 'error in the length of each portion measnred by 

 one observer is : 



0y.421 



± = i 0/^149, 



1/8 



and as the whole measn ring-bar consists of fonr portions, the mean 

 error in the length of the bar for each observer is 

 ± 0.-.149 1/4= ± 0/^298. 

 If the value of this mean error is formed by comparing with each 

 other the lengths of the nieasnring-bar according to each of the three 

 observers, we obtain : 



± 0/^355. 



From the agreement of the last two values we maj^ conclude, 

 that in the results obtained the influence of the observer and of the 

 position of the metre and the measn ring-bar is eliminated, and that 

 therefore, beyond the influence of the temperature determination and 

 errors in the coeflicient of expansion, the mean eri'or in the length 

 of the whole measuring-bar expressed in the length of metre 27, 

 determined by one observer, is equal to 



± 0/^36. 

 and is therefore for the mean of the three observers : 



0.36 



i/Z 



^ ± .205. 



Geodesy. — "Comparison of the Dutch pi it mum- iridium Metre 

 No. 27 lüitli the international MHre M, as derived from the 

 measurements hi/ the Dutch Metre-Commission in 1879 and 

 1880, a7id a pre/imina>-;/ determination of the length of the 

 measuring-bar of the French /jasj-apparatus in international 

 Metres" By Prof. H. G. van dk Sande Bakhuyzen. 



The main object of the measurements made by the Dutch Metre- 

 Commission (Bosscha, Oudemans and Stamkart) at Paris in 1879 

 and 1880 was an accurate comparison of the two Dutch metres 

 19 and 27 vv^ith the Metre des Archives, the various papers published 

 by Bosscha on tlie subject sliovv, how very well this object was 



2i'^ 



