ORIGIN AND PROGRESS OF GEODETIC SURVEY IN SOUTH AFRICA. 235 
was laid down. Its terminals were marked by fine holes in brass blocks, 
fixed on concrete pillars 2 feet square and 4 feet deep, founded on rock. 
Each pair of wires was compared a number of times on November 3, 
4, and 5 with the 400-foot ground standard before measurement of the 
base, and again on December 22 and 24 after measurement of the base. 
The length of the standard base for the measurements in November 
was computed from the results of the Cape comparisons in the preceding 
August and September, and those of December from the Cape com- 
parisons in the following January. 
The results are given in the following table, in three columns, for 
comparison— 
a. From all measures. 
b. From measures with wires not used in the base work. 
ce. From measures with the old wires only, and excluding the later 
measure with the C, D pair (D having been used on the base). 
Length of 400-foot Ground Standard.—A. 
1900 Wires a b c 
mm, mm. mm, 
November 3, 4, and 5, P and PP 121923°66 121923°66 — 
with lengths derived Q ,; D 24°81 24-81 — 
from Cape compari- Agr 706 23°20 23°20 121923:20 
sons in August and Gioteren, LD) 23°20 23 20 23:20 
September eos We 23°54 23°54 23°54 
December 22 and 24, = } nf he “ie cy 
with lengths derived A ene 93-53 93°53 93-53 
from Cape compari- C D 93-89 
* ” : = oa“ Saas 
sons in January 1901 BE) F 23-17 23-17 23-17 
Means . . 3 - _— 12192391 121923°59 121923°35 
Probable error . 2 _ +0716 +0715 + 0°06 | 
The wires A, C and EK were of steel. 
5 BS Drand sh 5 brass. 
” PandQ Pr nickel steel invar. 
= PP 5 nickel steel having a coefficient of expansion some- 
what like that of brass. 
The pairs of wires P, PP and Q, D were alone used for measurement 
of the base, but they were compared with the 400-foot ground standard 
before and after measurement of each section of the base, with the fol- 
lowing results, when corrected to the temperature at which both wires 
have the same length (Jiiderin method), assuming the 400-foot ground 
standard (S) to be constant in length. 
1900 P, PP Q, D 
. _mm. mm. 
November 3,4,5 . P é . 38. --3°61 18.—3°94 
a9 14, 15, 16 - A : —3:80 —3'96 
a R28 ‘ 5 A —3°76 —3:°95 
December 5. ’ - : : —3 82 —4:02 
ye ae ‘ 3 y —4-01 —419 
is 22,24° . s Z —4:28 —4:35 
