G-eodesy. — "Comparison of the measuring har used in the hasè^ 

 measurement at Stroe mith the D/itch Metre No. 27". UyU. G. 

 V. D. Sanue Bakhuvzen, N. Wildeboek and J, W. Dieperink. 



Ill tlie Slimmer of 1913, the Government-Commission for Triangii- 

 latioii and Levelling measiiicd a base of about 4320 metres, under 

 the direction of Prof. H. J. Keuvelink, on the high road between 

 Apeldoorn and Amersfoort, near the Railway-station Stroe. 



The measurements were made with the base-apparatus of the 

 "Service géographique de l'armée" at Paris, which was lent through 

 the courteous help of the Director of that service to the Government 

 Commission bv the French Government. 



The measuring bar of this apparatus is an H-shaped invar-bar of 

 four metres length, provided with two very sharp end lines at the 

 extremities, between which three intermediate lines are drawn, which 

 divide the measuring bar into four parts, a, b, c and d, each one 

 metre long. 



Previous to the base measurement here, this measuring-bar had 

 been compared several times with the metre international at Breteuil ; 

 these comparisons had shown, that the length had undergone some 

 slow changes, as is often the case with invar-bars ; it was therefore 

 important to determine the length shortly before and after the base- 

 measurement. 



In April 1913 therefore a comparison was made at Breteuil, but 

 as the comparator there had to undergo some repairs, the comparison 

 could not be repeated in the autumn of 1913 ; it was therefore 

 decided to compare the measuring bar in this country with one of 

 the two Dutch pialinnm-iridium metres, viz. with No. 27, by means 

 of t''e comparalor which had been supplied by messrs. Repsold and 

 Sons in 1867 wiih the base-apparatus for the triangulation in the 

 East Indies, and which is now mounted in the geodetic buildings in Delft. 



From the experience gained in previous measurements we did not 

 consider that sutTicient accuracy could be obtained with this compa- 

 rator, especially on account of the inferior quality of the microscopes ; 

 on this account it was decided to order two new micrometer-micros- 

 copes from Zeiss (in Jena) which were delivered in the autumn of 

 1913, so that in December the comparator was ready for the comparison. 



We are very much indebted to Prof. Heuvelink, who arranged 

 everything for the measurements and placed a room in the geodetic 

 buildings, and an instrument-maker at our disposal for some weeks ; 

 and fiirllicr to the "Commission for the preservation of the stan- 

 dards", who allowed us the use of metre 27. 



