138 MEASUREMENT OF BASE LINE. 
5. Errors in micrometers. This would necessarily be very 
small, if any, as the micrometers are only responsible for the 
measurement of 1:018 inches of the whole base. 
The extreme error possible under any of the above—Nos. 1 
and 2—would not exceed an inch, and in the others it would 
amount to a very small fraction. Having given the question 
careful consideration it was determined not to make any allow- 
ance for these small errors. 
I have endeavoured to give a general idea of the details of the 
measurement, avoiding as far as possible technicalities which 
would only be understood by the profession. As a rule the 
general public take little interest in the execution of these 
surveys. They may acknowledge them to be necessary, but do 
not care to know the processes by which they are carried out. 
I am glad of the opportunity the Royal Society has afforded me 
of placing the results of the measurement on record, and trust 
I have succeeded in interesting the members whilst dealing with 
a somewhat dry subject :— 
APPENDIX A. 
DETERMINATION OF THE LENGTH or Tapes A AND B USED IN 
MEASUREMENT OF Basz LIne. 
100FT. APPROX.—TAPE A. 100FT. APPROX.—TAPE B. | Tea 
Date of Mea- | Tempera- | Length at 62deg. || DateofMea- Tempera- | Length at 62deg. || 
surement. ture. * | Faht. surement. | ture. Faht. 
1883. FEET. 1883. FEET. 
Sep. 14 66°5 99°9977453 || Sep. 14 67:9 99°9969864 
a aD 66°0 99:9978127 3 LD 66°5 99°9970344 
Nowe 7) 72:5 99:9983970 || Nov. 8 72°70 | 99°9977527 
a ath 730 99°9980835 ee ris) 735 99°9974.246 
Uf TBES 99°9980573 ng (aio 99°9975248 
May 16 |. 61:0 | 99°9975325 May 16 63:0 | 99°9976441 
epee le 61:0 99°9975197 Le. 62°5 99°9978327 
Aug. 8 640 | 99:9982328 || Aug. 7 64°0 99:9973815 
a ats 64°5 99°9985049 sae LOY) 65:0 | 99°99806381 
aD) 63°5 99:9986753 song 64°5 99°9985667 
Nov. 1 72-0 99°9968217 || Nov. 1 740 99°9976355 
ee) 72-0 99°9964533 
Adopted mean - 99:9980561 Adopted mean - 99.9976211 
