162 
NATURE 
[JUNE 15, 1899 
running with a strong current in a devious channel amongst the 
bars and mud flats, which are left dry at low water. 
The run of the rising tide first breaks into a bore at Stony 
Creek, eight miles below Moncton, and it continues to the 
head of the estuary at Salisbury, thirteen miles above. The 
total distance on the river that a bore occurs is therefore twenty- 
one miles, 
With regard to the time of arrival of the bore at Moncton, 
this really corresponds with the time of half tide. At the 
central moment between the previous and the following high | 
water, which we may term the theoretical time of low water, 
the level of the water in the river is still falling ; and it con- 
tinues to fall, though at a much slower rate, for about three 
hours longer before the bore arrives. The time of the arrival 
of the bore is thus only about three hours before the next high 
water, which serves to account for the very rapid rise which 
takes place after the bore passes. 
The rate at which the tide falls amounts at its maximum to 
eight feet per hour ; but after the theoretical time of low water, 
the rate of fall soon becomes very slow,.and the river appears 
to a casual observer to remain at the same level for some two 
hours before the arrival of the bore. The flow, however, con- 
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the wharf at 23h. 19m., or eleven minutes after its sound was 
first heard. The rapidly-flowing layer of incoming tide ad- 
vanced over the current of the river in the opposite direction, 
with a front of broken and foaming water, which had a height 
of perhaps two or three feet. The front edge was by no means 
straight. The higher part of the bore extended across the 
waterway, and this was bent back and also heightened in the 
middle by the opposing current of the river, which is naturally 
swiftest at the centre of the stream. Beyond this the bore 
formed a long sweep, where it broke over the flats, retarded and 
decreasing in height towards the further bank of the river. 
The surface current of the water following the main front has 
the same speed of flow as its rate of advance; and after the 
main front passes, there usually follow a series of others, 
stepped up a few inches of additional height. These form 
irregular lines of curve across the surface of the advancing tide, 
which do not extend far without interruption. These may be 
due in part to back-wash from the flats into the main channel. 
As seen in the day-time, the water forming the bore is exces- 
sively muddy and reddish-yellow in colour, just as the out- 
flowing water of the river also is. The actual broken water in 
the front is nearly white, except at the shore end ; but the long 
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2 MILES. 
CORRESPONDING SCALE OF DISTANCE 
FROM AVERAGE SPEED OF BORE. 
AVERAGE SPEED AS OBSERVED 
tinues to be fairly swift ; and it no doubt still consists of tide | 
water. The rate of fall in the level of the water, as measured 
shortly after spring tides, was found to be as follows :— 
From 4 to 24 hours before arrival of bore, rate of fallsix inches per hour. | 
Pe ey akeliag  geveyehe os * on 0 four inches nn 
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The first observation of the bore was made on the evening of 
August 4. The point of view commanded some two or three 
miles down stream below the bend, as well as the foreshore op- 
posite Moncton. The moon was a little past the full, and was 
well risen before the bore arrived ; and the sky was then clear 
also. There was a very slight breeze, and in the stillness sounds | 
could be distinctly heard. It was thus at the spring tides, and 
twenty-four hours after the lowest of the tides at that moon. | 
The first sound of the approaching bore was heard at | 
23h. 8m., in 60th meridian time, and two minutes later the 
sound was quite distinct. This sound was very similar to the 
noise of a distant train when heard across water. It afterwards 
increased to the usual hissing and rushing sound of broken water, 
as in a rapid on a river; but there was no mingling in this 
sound of any roar, such as a waterfall makes when falling into 
deep water, even from a moderate height. The bore arrived at 
NO. 1546, VOL. 60] 
@-47 mites PER HOUR. 
edge of the advancing water on the flats appears nearly black in 
strong sunlight. With a stiff breeze down stream, the sound of 
the bore cannot be heard till it has approached within a few 
hundred yards. 
During the neap tides the bore still appears, and the front 
edge usually breaks a few inches high. But there are times 
when it consists merely of a heavy ripple, like the side waves 
from the bow of a steamer when they are advancing over still 
water ; and it then only breaks occasionally, except in passing 
over the flats. 
The rate of advance of the bore was timed from a point of 
observation on one of the upper wharves, which commands a 
view around the bend of the river. The velocity, as determined 
from several observations, was about 84 miles an hour. 
To ascertain the form of the bore, and its rate of rise, a 
graduated board 13 feet high was set up in the front of the 
wharf, at which the tide gauge was placed. The current, after 
the bore passes, appears to have the same surface velocity as the 
rate of advance of the bore itself. 
The height of the bore, as observed at spring and neap tides, 
and the rise of the water following it, are shown in the report 
| by diagrams, of which one is reproduced here. The rise is by 
