258
6
In comparing the high and low waters at Canton and Whampoa, I assume that the spring rise varies as the mean range. Owing to the varying slope of low water from mouth to mouth this is not, of course, strictly true, but it will be found to serve well enough to give indications of changes,
In 1891 the means of high and low waters at each full and change were as follows:-
7
Collecting these differences, we see that the Canton gauge varied in its conformity with the Whampoa gauge as follows:-
High water
Low
Range
Canton.
Whampoa,
Ft. in.
Ft. in.
12 10-2
8 5.6
$ 0-2
2 6.4
4 10
511-2
Now, on the supposition that we wish the zeros of these gauges to conform at the mean of the river, and taking Whampoa as a standard, we ascertain that the mean high water at Canton should have been by the following proportion:-
5 ft. 112 in. : 4 ft. 10 in. :: 8 ft. 5-6 in. : 6 ft. 107 in.
ie., had Canton gange been set to couforia with Whampoa gange (at the meau condition of the river), its mean high water would have been 6 ft. 10-7 in., but actually it was 12 ft. 10-2 in., že..
5 ft. 11.5 in. too much.
It is evident, then, that the raising of the Canton gauge in 1900 to the extent of 6 feet, to make it conform with the Whampoa gauge, was about right.
I will now make a comparison for the twelve months from June 1908 to May 1904, to ascer- tain whether at that period any change in the conformity of the zeros had occurred.
For the year 1891 I took a Table already existing. For the period June 1903 to May 1904 I have had the mean of the daily high and low waters for the several months worked out, as the change in conformity month by month is instructive.
1903-
June
July
August
September
October
November
December
1904-
January February
March...
April
May
Too Much.
Too Little.
Feet,
Feet.
1.3
15
0.3
0.6
0-3
0-1
0.2
0'2 0.7
The means of these non-conformities is 0-4 foot too much,
Wo see, then, that in 1891 the gauges conformed almost exactly at the mean conditions of the river, but that in the year June 1903 to May 1904, at the mean condition of the river, the Canton gauge is calculated to have shown 04 foot too much.
This is fairly conclusive evidence that the 05 foot which I found the gauge to be out in June 1904 was due to its subsidence, de,, we have good reason to suppose that in November 1893 the gauge was correct, and that in June 1904 it was 0-5 foot too low.
In order to obtain a correction for the 1903 records, it is necessary to assume that the gauge sank uniformly. On this supposition the mean error of the gauge for 1903 would be 0:37 foot too low.
Date.
Cauton.
Whampoa.
1903-
Feet.
June
High water
7-4
Low
3.1
Ft. in. 8 1.6 2 5.3
Range
4.3
5 83
Remarks.
Hore deducing what Canton should have shown from the proportion between the ranges, we find that Canton should have shown 6'1 feet instead of 74 feet, i.c., it showed 13 feet too much,
0'5 foot.
0-37 foot.
Feet,
July
High water
Low Kange
...
October
August
September
High water
Low
Range
High water
Low Range...
High water
Low
Range...
75
November
High water Low
Range
December
...High water
Low
Range ...
1904
January
High water Low
Range...
February
High water
Low
Range
March
April
Low
Range ...
High water
Low
High water
JF
17
Range
May
High water
Low
27
Range
+
382 383 323 332 633 ANG ANN AUX 283 382 383
8-4
3.7
2.9
4.2
5.5
Here Canton should have shown 04 feet, i.e., it showed 1-5 feet too much.
8:0
Canton should bave shown 6-9 feet,
2.2
i.e., it was 3 feet too much.
5-8
8-%
Should have shown 7 feet; 0'6 fout
2.6
too much.
5+7
January 1901.
November 1900.
January 1902.
January 1903.
June 1903.
January 1914.
June 1904.
7.3
8.4
Canton showed correctly.
2.5
2.9
48
5*5
We are now ready to compare the ascertained means of the recorded high and low water at Canton for the years 1882, 1888, 1893, 1898, and 1903 --
7:0
8.0
24
2.5
Should have shown 6'7 feet; 0.3 foot
too much.
Mean of recorded-
4.6
5-5
6.6
7-8
Should have shown G'5 feet; 0'1 foot
Range.
2.0
2.3
too much,
High Water.
Low Water.
5.5
Ft. in.
Ft.
in.
6.7
7-8
2.3
Should have shown 6.8 feet; 0.1 Foot
too little.
1882
12 9.6
8 10
Correction for altered setting
8 00
0 0·0
4-8
5.5
6 0.6
6-4
7.6
Should have shown 6'6 feet; 0.2 foot
2 1.0
1-5
2-0
too little.
In feet and tenths
6.80
2:08
4.72
49
5-6
1888
***
12 9.5
8 5.7
6.7
7.7
Canton showed correct.
Correction for altered setting
€ 0.0
6 0.0
1-8
2+1
5'6
6 9.5
2 5-7
7-9
Should have shown 67 feet; 0-2 foot
In feet and tenths
6-80
2.48
4.32
10
2.0
too much.
5:0
5.9
1893
.-་
12 5-7
8 31
8:0
Should have shown 6-7 feet; 0.7 foot
Correction for altered setting
6 0'0
6 0·0
2-5
2.2
too much.
6 5.7
2 3·1
4.9
5.8
In feet and tenths
[2288 6-1]
6.18
2.20
4.20
D
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