TRIGONOMETRICAL SURVEY OF NEW SOUTH WALES. 237 
assumed in the computations do not well represent the surface of 
Tasmania, or that there are considerable local deviations of the 
vertical. Possibly both these causes contribute in some degree ; 
the latter may certainly be expected to have effect from the 
rugged nature of the country covered by the survey. The 
writer is unaware of the elements adopted, but in some of the 
computations appended to Major Cotton’s account of the triangula- 
tion, read in 1855 before the Royal Society of Tasmania, and from 
which much of the above information has been drawn, a mean 
radius of 20,887,457 feet has been used. The whole of the survey, 
it should be stated, was executed by Mr. J. Sprent, under Major 
Cotton’s direction. 
For some thirty years or more no other application of the 
trigonometrical survey appears to have been made, than by its aid 
to construct a framework for the projection of a map of the 
Colony, and on one occasion at least its general accuracy has been 
assailed, for reference may be found in the Tasmanian Royal 
Society’s Proceedings, as lately as the year 1881, to its having 
been challenged by the late Mr. Calder, a former Surveyor- 
General of the Colony. However, the opinion expressed by Mr. 
Black, of Victoria, when, in 1883, reporting on the system of 
surveying in Tasmania, seems a most feasible one. His view was 
that ‘It is quite possible that the erroneous character of much 
of the topography of Mr. Sprent’s map may have given rise to the 
impression that the whole data is worthless ; but it by no means 
follows that this is the case because some person evidently 
imperfectly acquainted with the country has sketched the features 
incorrectly.” 
Some attempt has recently been made to put the triangulation 
to some service, and during the years 1884-6 some forty of 
the stations were rebuilt. Many others, however, are, it is 
understood, not now recoverable. The cause of its having fallen 
into desuetude was no doubt the fact that it was not combined 
with a sufficient amount of minor triangulation to enable proper 
connection of the chain surveys to be made, without having to 
run traverses for long distances, and often into country presenting 
the greatest difficulties in the way of chaining. The advantages 
offered by a trigonometrical survey have now been fully recognised, 
and some five base-lines have been measured for the purpose, 
doubtless, of carrying out any future extensions on the New 
Zealand scheme of initiating purely local systems which become 
eventually joined into one comprehensive survey of the whole 
country. 
