236 REPORT —1905. 
It will be seen from this and the preceding table that the hard work 
of base measurement has a tendency to induce molecular change in the 
wires, and that the wires left at comparative rest give more consistent 
results for the standard ground base (see column c of preceding table). 
It is also evident that new wires have a tendency to contract. 
This latter point will be more evident from the following table of the 
lengths of the wires at 70° F. at the different epochs when their absolute 
lengths were determined at the Royal Observatory. 
A B Cc D E F 
ihe Steel Brass Steel Brass Steel Brass 
mm. th mm. mm, | m mm. mm. 
| (1) April-May, 1898 » |24383°93 |24386°23 |24384-36 24386 18 |24383- 57 |24385-94 
(2) Oct.—Nov. 1898 5 82°65 $5°67 84:17; 86:04) 82°57 85°42 
(8) April-May,1900 , 82°63 86:01 84:13 86:03 | | 83:12 85°77 
(4) Aug.—Sept. 1900 : 82:40 85°73 83°91; 85°79) 82°81 85:19 
(5) Jan. 1901 ‘ 82:15 85°58 83°71 | 85:84 | 82°64 85:02 
The wires P, PP and Q were only supplied in 1900. 
(1) and (2) were the comparisons made before and after the measures 
of the Inseza base near Bulawayo, of which I give here no further details, 
as it does not enter into the great arc of meridian ; (3) was an inter- 
mediate comparison ; (4) and (5) the comparisons of the wires made 
before and after the measures of the Inseza base. 
The length of the 400-foot ground standard was adopted from the 
mean of the measures with all the wires before and after the base 
measurement. 
The adopted lengths of the measuring wires for each section of the 
base were the mean length derived from their comparison with the 
ground standard before and after the measurement of that section. 
Each section of the base was measured both forwards and backwards 
by both wires. The following are the results :— 
Section Bi ra io Gi ak Discordance 
mm. mm. 
Ia e 5 5 1,646,525 1,646,530 lin 329,000 
b H . 4,020,152 4,020,130 FS 163,000 
II. . : | 3,144,434 3,144,433 », 3,100,000 
Ill. a 5 3,530,470 3,530,492 * 161,000 
b ‘ ‘ -| 1,595,383 1,595,382 » 1,600,000 
1V. a és j 3,715,304 7,758,926 » 431,000 
b - 4,0436,40 — — 
21,695 908 21,695,893 1 in 1,446,000 
— | 
The adopted mean length is 21,695,901 mm, 
71,181°419 feet. 
I have gone into this detail in connection with the measurement of 
the Gwibi base because it is certainly the least accurate of the base lines 
that occur on the great are of meridian, 
