6 ANNIVERSARY ADDRESS. 
and asked him for futher particulars of the rise going on in Vic- 
toria ; and in reply he said that Mr. Clarke had in some way mis- 
understood his remarks, which had reference to the silting up of the 
harbour—not the elevaticn of the land ; and he at the same time 
sent me a copy of his paper on “ The Tidal Datum of Hobson’s 
Bay,” read before the Royal Society of Victoria, August 14, 1879. 
After givingthe history of the tide-gauge, which wasstarted in 1858, 
under the Harbour Department, and was not under his control 
until 1874, Mr. Ellery says :—‘“ It is to be regretted that no pre- 
cise references to mean tide-level in the earlier days can be found. 
Where measurements do exist in Hobson’s Bay, they are lacking 
in accurate information as to the state of the tides, and I find 
nothing trustworthy upon which to base any statements as to 
change of sea level since surveys have been made, I think it 
desirable that permanent bench-marks on the natural faces of the 
rock in sitw should be established around our bay, carefully con- 
nected by accurate levelling with one another and with the tide- 
gauge, for it is very doubtful if bench-marks on buildings can be 
assumed to afford a permanent datum.” 
The first self-registering tide-gauge in Sydney was erected on 
Fort Denison, by the late Mr. Smalley, in 1867. Unfortunately 
the design was so faulty that all the records of the heights of 
tides made by it are of no value, although the times of high and 
low water are correct. The reason for this fault in its records was 
that an ordinary hempen cord was used to connect the float and 
the pencil, and this gradually got longer by use, and also varied 
with the weather. Finding it impossible to remedy this fault 
satisfactorily, in view of the necessity for exact records of the 
heights of the tides, in 1872 I had anew gauge made, which, 
without losing the accuracy of the time record which the old one 
possessed, ensured the correct record of the height of the tides. 
This instrument is figured and described in the “Sydney Meteoro- 
logical Volume for 1878,” and to that work I must refer you for 
particulars. The record by the new gauge was begun on June 27, 
1872, and at that time the precaution was taken of measuring the 
