178 



EEPORT — 1882. 



The corrections as thus obtained are inserted in Table XVIII., 

 Column I. In Column II. are given (for the sake of comparison) the 

 corrections calculated from the observed instead of the transferred thread- 

 lengths. The greatest difference is 0°-005. 



This example will have made Rudberg's method clear. The correction 

 for the middle part, C, of a tube A B, is obtained by measuring a thread 

 approximately equal to A C or B C with its extremities at A and B in 

 turn. 



A C B 



A thread approximately equal to ^ the length of tube is measured in 

 the positions A d, d e, e B. Hence its true length and the corrections at 

 d and e are found. By then measuring it in the positions C/ and C g, 



d e 



since its length and the correction for C are kno-wn, the corrections for 

 f and g are found, and the tube is thus divided into six parts. 



f d eg 



Next, to divide the tube into 12 parts, a thread = -fh of its length 

 is taken. The true length of this and the correction for h are determined 



A 



h c Jc I 



m B 



/ 



d 



9 



by measuring it in the positions A 7j, li g, as the corrections of A and g 

 are known. An independent value of the length and the correction for 

 % may be found by measuring fk, k B. In the present case the two 

 values of the length differ only by O'OOIS. That determined from Ag 

 has been used. By measuring forwards from d and C the corrections for 

 I and m are found, and by measuring backwards from e and C, those for 

 n and o. 



To divide the scale into 24 parts a thread ^^ of its length would be 

 used, and so on. 



