THE RIVER THAMES AT LONDON BRIDGE AND THE SEA. 187 
The mean high-water mark, taking every high water through the months, is 
as follows : 
1828. 
1829. 
January - - . 
. . 17-342 
. . 16.904 
February . . 
. . 16.904 
. . 16.804 
March . . . 
. . 17-070 
. . 17-208 
April .... 
. . 16.925 
. . 17.270 
May .... 
. . 17-352 
. . 17.175 
June .... 
. . 17-258 
. . 17-091 
July .... 
. . 17-595 
. . 17-350 
August . . . 
. . 17-466 
. . 17-100 
September . . 
. . 17-345 
. . 17.591 
October . . . 
. . 17-000 
• • 55 
November . . 
. . 17.001 
. . 17.412 
December . . 
. . 16.691 
. . 16.787 
Means 
. . 17-1624 
C- 
. . 17-1538 
17.1581 
The difference therefore between the mean of 
spring and neap tide and the 
means of the months, as above, is 
(17-1581-16.947) 0.2111. 
The index mark xxi at the canal is 0.2110 + 4.0661 = 4.2771 above spring 
tide high-water mark at Sheerness ; and the spring tide high-water mark at 
the Regent’s Canal being 19.233, 
xxi — 19.233 
= 1.767, and 4.2771 - 1767 
= 2.5101, the height of mean spring tide high-water mark at the Regent’s 
Canal above the same at Sheerness. 
The index mark xxi is also 6.1321 above mean high-water mark at Sheerness. 
And the mean high-water mark at Regent’s Canal being 
16.947, xxi - 16.947 = 4.053 and 6.1321 — 4.053 = 2.0791 
or 17-1581, xxi - 17.1581 = 3.8419 and 6.1321 - 3.8419 = 2.2902 the 
height of mean high-water mark at the canal above the same at Sheerness. 
And the mark xxi is 7-9761 above mean neap tide high-water mark at 
Sheemess. The mean neap tide mark at the canal being 14.662, xxi — 14.662 
= 6.338 and 7-9761 — 6.338= 1.6381, the height of mean neap tide high 
water at the canal above the same at Sheerness. Therefore the water of spring 
tides at the canal above spring tides at Sheerness is higher by 0.8720 than it 
is at neap tides at both places. 
2 b 2 
