ge 
WATER CONSERVATION SURVEYS OF N.S.W. LXXXIII. 
Distance Error of Error of mr innawse theese 
No Levelled. Close. 1 foot in Water 
Miles. Feet. Miles. and es Railways. Conservation. 
1] 1300 1°56 e333. | 886 |... | 450 
2 392 “54 726 S 189 203 
3 1394 “50 2788 850 264 280 
4 721 2°34 308°1 ae 291 430 
5 1597 5:07 315 957 640 
6 1020 2°42 421°4 1020 
: 2240 2°10 1066-6 850 890 560 
8 590 1°68 351-2 370 220 
9 1203 1:33 904°5 853 350 
10 513 1:22 420°5 203 310 
11 340 1°51 225'1 140 200 
12 330 1°71 193 70 260 
11640 “S196 4 CRE ee 
in 2,788 miles in No, 3, to 1 foot in 193 miles in No. 12, while 
the mean closing error on the total distance levelled sinsunted to 
1 foot in 529% miles. To the surveyor, this information was of 
very little value without a knowledge of the country levelled over, 
and the circumstances under which the levels were taken. 
this subject the paper did not touch, the author no doubt think- 
ing that most of his hearers would have a good idea of the class 
of country traversed, from being residents in the Colony ; but in 
the interests of readers in other parts of the world, it was to be 
regretted that this information had not been given. In all reports 
on levelling operations by the Survey Department of India, in 
the Geodetic Survey of the Cape of Good Hope, the United States 
Coast Surveys and various other valuable scientific reports, the 
rises and falls, number of bench marks laid down, and the class 
of country traversed, were all enumerated as having an important 
bearing on the subject, and allowing those interested to form an 
Opinion on the value of the close. 
Tt was perhaps unnecessary to state that the value of a line of 
levels was by no means to be gauged by a knowledge of the clos- 
ing error only. The writer .d on various occasions made the 
