ANNIVERSARY ADDRESS. rf 
length of the chain connecting the float and the wheel, so that 
should any change take place its exact amount could be ascer- 
tained. The wisdom of this has been evident on several occasions 
when the chain was broken by accident and the exact length 
restored. The well made for the tide-gauge is in part cut in the 
solid rock, and from the rock to the surface of the ground the 
sides of the well are built up (round) with solid masonry, so that 
the top ring of the well is practically part of the solid rock, and 
cannot move unless the rock does so. On this ring the frame of 
the tide-gauge stands, and the instrument, therefore, has a per- 
manent relation to the rock, and there can be no change in its 
parts which might be mistaken for a change in sea-level. 
I have been particular in detailing the conditions under which 
the tide measurements have been made, to show you that sufficient 
precautions to ensure accuracy have been taken. In each year 
the mean of all the tides is taken as the mean sea-level for that 
year, and when these results for the past twelve years are placed 
side by side, it is at first sight rather puzzling; for although the 
greatest departure from the mean of all is only 1 inch, yet within 
this small range the land seems to rise and fall in an erratic way. 
The cause of these variations, however, was found in the varying 
relative positions of sun, moon, and earth, and perhaps to some 
extent in the effects of heavy gales. Taken as a whole, these 
results seem to prove conclusively that no change whatever has 
taken place in the relations of land and sea during the past twelve 
years. Of course the question is not settled—a slow change that 
would be visible in centuries might be altogether hidden in the 
results before us; but so far as they go these results will be 
interesting to scientific men, for they are the first that have been 
taken with such accuracy as the investigation demands. 
Mean sea-levels :— 
1873... ws 2 feet 59 inches 
Mihi ke ek ae 
1875. Da ee 
1876... 6 a Bes 
