TRIGONOMETRICAL SURVEY OF NEW SOUTH WALES. 235 
greatest east and west elongations, but the instruments used were 
only the same small ones employed in the terrestrial work. The 
time is looked to, however, when the whole of the survey will be 
the object of a little more consideration from those in charge of 
the purse-strings, so that this extensive triangulation, which now, 
with only one small gap, covers nearly 19 degrees of longitude 
and 17 of latitude, may be made available not only for all the 
needs of land administration, but also may be made to contribute 
to our knowledge of earth shape and size. 
TASMANIA, 
The trigonometrical survey of this colony may be said to have 
been initiated in 1849, when the first measurements were made 
of a base line, nearly 4 miles in length, at Ralph’s Bay. Rods 
of fir, each 15 feet long, protected by a covering case and insulat- 
ing material, and fitted with brass caps at the ends, were used, 
and the general slope of the ground was followed, corrections for 
the inclinations of the rods being applied. The brass caps of the 
ends of the adjacent bars were brought side by side, and a scale 
fitted to one was read by a vernier engraved on the cap of the 
next bar. The lengths of the rods were ascertained by comparison 
with a 4-foot steel standard divided into inches and fortieths, 
comparisons being made from time to time during the operations. 
This was, at the time, the only standard in the colony ; but 
shortly afterwards a 10-foot steel bar was obtained from England, 
and on the older one being compared with it, the two were found 
to be in such very close agreement, that Major Cotton stated in 
a report of his on the subject in 1852, that the measurement 
required no reduction on this account. 
This later standard was one of those employed in base-line 
measurement for the Ordnance Survey of Ireland. Its length, 
therefore, may be assumed to have been well determined. The 
same base was afterwards measured twice in 1851, when the 
earlier results were found to differ from the mean of the later, by 
about 10 inches; the mean of the later determinations, over 
which greater precautions had been taken, and which differed 
only by slightly more than an inch, was adopted. 
A base of verification nearly 5 miles long was measured twice 
by similar means, at Longford, on the Norfolk Plains, the two 
measures differing only by 3} inches. The bases, which were 
about 100 miles apart, were connected by a system of triangles, 
the angles of which were measured by repetition with a 12-inch 
altazimuth graduated to 10 seconds. The greatest error of close 
on this system was 3:3, a result which points to the accuracy of 
the instrument and to the care taken in making the observations. 
A further proof of the accuracy of the work is given by the fact 
