56 CAPTAIN SIR E. BELCHER ON THE TIDE OBSERVATIONS AT OTAHEITE. 
which the rod traversed freely. Above the trunk, secured to strong uprights, step- 
ping into its exterior sides e, e, the graduated battens rose, having a clear space 
between them, and very neatly and strongly graduated with black divisions on a 
white ground. 
The index had a clamp tube, through which the gauge-rod passed, f, when it was 
finally clamped at the first high water. 
The index was a piece of machinery, per se,ff. It was furnished with fore, as 
well as back, friction rollers, on springs, amounting to eight, by which it maintained 
its position steadily, and kept the gauge-rod perpendicular. This machine had been 
well tested at Bow Island and its imperfections obviated. 
This gauge was fixed upon the abrupt steep of the reef in ten feet water, and well 
ballasted by pigs of iron, on which it also rested. It was distant from the wall 
thirty yards, and easily read off by a telescope. It was registered during daylight 
(from 6 a.m. until 6 p.m.) from the top, so that the least number indicated high water, 
and vice versa. 
The tide-batten was lashed to the rocks (similarly ballasted) close to the wall of 
Motouta, in four feet water, and a thick plank enabled the observer to take the 
closest inspection. It was registered from the bottom by day as well as night, and by 
day at the same periods as the tide-gauge. The greatest number therefore indicates 
high water. 
As it is almost impossible to determine the actual moment of high or low water, I 
had recourse to the method of equal altitudes, within two hours on each side; as the 
results of my observations on the coast of Lancashire, where the water was subject 
to a rise and fall of thirty-one feet, always coincided up to the latest half hour. 
I have been thus minute in order to satisfy any sceptical minds bent on the main- 
tenance of the absolute noon period, that the minutest attention was devoted to this 
duty, and the coincidence of the two observers, five miles asunder, will in some points 
be found to agree minutely. 
It will be seen by reference to the mean tide-levels, subsequently reduced for each 
day (and not contemplated by the observers themselves), how strictly this duty was 
attended to, the range never exceeding two inches on either gauge or batten. 
The position at Matavai was at the extremity of Point Venus, which was shielded 
in a great measure from the influence of the sea, by reefs similar to those at 
Papiete ; but here we had merely tide-battens ; the observations, however, were cor- 
roborated by repetitions within the rivulet, on a pole with crosses to mark the 
simultaneous levels, the more readily to deduce the moments of high and low water. 
These were watched for the last week by Mr. Christopher George, second master, 
my general assistant in the observatory, and superintendent of the tide-journals. 
These data (from the 22nd to the 27th) are comparable with those observed at 
Motouta. 
By these documents it will be observed that there were two irregular moments of 
