Giving the vulgar establishment or time of high water at full and change, and the rise and fall or whole range at spring and neap tides, except for the United States.

PLACES.

Time of H. W. at full and change.

Range at spring tides.

Range at neap tides.

EAST COAST OF ATLANTIC OCEAN.

h. m.

feet.

feet.

Simon's bay, Cape of Good Hope...

2 44

St. Helena island ....

3 11

3

St. Paul de Loanda, Africa

4 30

5

Sierra Leone, " .........

7 55

8

.....

Cape Verd, " .........

7 45

5

. . .

Ceuta, straits of Gibraltar

2 6

Gibraltar, old mole................

2 20

. .

Fayal, Azores

11 45

4

Cape Finisterre, Portugal

3 0

15

. . .

Bordeaux, France

6 50

14

11½

Brest, " .................

3 47

19

St. Malo. " .................

G 5

3.5

17

Cherbourg

7 49

17

Havre, " .................

9 51

22

14

Calais, " .................

11 49

19½

11½

Dover, England .......

11 12

18¼

11¼

Portsmouth dockyard, England

11 41

12½

Plymouth breakwater, "

5 37

15½

PLACES.

Time of H. W, at full and change.

Range at spring tides.

Range at neap tides.

EAST COAST OF ATLANTIC OCEAN.

h. m.

feet.

feet.

Scilly isles, St. Agnes, England . . . .

4 30

16

8

Bristol (King road), " . . . . .

6 65

44

22

Liverpool, " . . . .

11 23

26

14½

Glasgow, Scotland . . . . . . . . . . . . . . .

1 25

9

6

Stromness, " . . . . . . . . . . . . . . .

9 0

10

5

Aberdeen, " . . . . . . . . . . . . . . . .

1 0

12

8

Leith, " . . . . . . . . . . . . . . . .

2 17

16½

9

Hull, England . . . . . . . . . . . . . . . . . . .

6 29

20¾

11¾

Yarmouth roads, England . . . . . .

9 15

6

2

Margate, " . . . . . . . . . . . . .

11 40

15½

10½

London docks, " . . . . . . . . . . . . .

1 57

19½

14½

Cape Clear, Ireland . . . . . . . . . . . . . . . .

4 0

9

4

Cork (Penrose quay), Ireland . . . . . . . .

4 58

12¾

Dublin bar, " . . . . . . .

11 12

12 - 14

7 - 9

Galway, " . . . . . . .

4 35

14¾

Ostend, Belgium . . . . . . . . . . . . . . . . .

12 25

19

11

Texel (outside shoals), Holland . . . . . .

6 30

4

3

Helgoland, Elbe entrance . . . . .

11 33

Loffoden islands. Norway . . . . . . . . . . .

12 0

9

6

Keret's point, gulf of Archangel . .. . . . .

4 30

. . .

WEST COAST OF ATLANTIC OCEAN.

Cape Horn islands, South America.

3 50

8

. . .

Santa Cruz river, " "

9 30

40

18

Rio Janeiro, " "

3 0

4

2

Cape St. Roque, " "

. . .

8 - 10

. . .

Maranbam, " "

7 0

17½

. .

Cartagena, " "

11 0

½

Cape St. Antonio, Cuba . . . . . . . .

. . .

. .

Bermudas, dockyard . . . . . . .

7 14

4

. . .

Greytown, Nicaragua . . . . . . . . . . . . . . .

9 0

. . .

Vera Cruz. Mexico . . . . . . . . . . . . . . .

. . .

2

. . .

Cape Sable, Nova Scotia . . . . . .

8 30

9

4

St. John's, New Brunswick . . . . . . . .

11 23

23

17

Sackville, " " . . . . . . . . . .

11 48

50

24

Halifax harbour, Nova Scotia . . . . . .

7 49

6

2

Quebec, Canada . . . . . . . . . . . .

6 38

18

8

St. John's, Newfoundland . . . . . . . . . .

7 30

7

. . .

Upernavik, Greenland . . . . . . . .

11 0

8

. . .

Van Rensselaer bay, Greenland . . .

11 50

11

INDIAN OCEAN AND WEST COAST OF PACIFIC.

Mozambique harbour, Africa . . . . . .

4 15

12

. . .

Bab-el-Mandeb, Red sea . . . . . .

12 30

. . .

. . .

Suez bay, head of gulf, Red sea . . . . .

2 0

6

. . .

Surat, Hindostan . . . . . . . . . . .

4 0

19

. . .

Bombay, dockyard, Hindostan . . . . .

11 40

12 - 17

. . . . .

Maldives, Adou atoll . . . . . . . .

1 0

4

. . . .

Trincomalee harbour, Ceylon . . . . . .

8 18

2

1

Madras road, Hindostan . . . . . . . . . . .

7 34

. . .

Western entrance to Hoogly river. . .

10 0

10¾

. . .

Singapore, new harbor . . . . . . . . . .

9 45

10

5

Batavia, Java . . . . . .

10 0

2

. .. .

Canton river (entrance). China . . . . . .

10 0

8

. ..

Yangtse-kiang (entrance), China . . . .

12 0

15

5

Nagasaki bay, Japan . . . . . . . . . . . . .

6 28

6 ¼

. . .

Sydney, Australia . . . . . .

8 38

Melbourne " . . . . . .

1 20

3

. . .

Tahiti or Otaheite island . . . . . .

noon

1

. . .

Honolulu, Sandwich islands . . . . . . .

4 0

2

. . .

EAST COAST OF PACIFIC OCEAN.

Cape Virgin, strait of Magellan___

8 30

36 - 42

. . .

Cape Horn . . . . . .. .

4 40

9

. . .

Valparaiso, Chili . . . . . . .

9 32

5

. . .

Callao bay, Peru . . . . . . .

5 47

4

. . .

Guayaquil, Ecuador . . . . . .

7 0

11

. . .

Panama road, Colombia . . . . . .

3 23

15 - 22

5 - 10

Port la Union, gulf of Fonseca

3 15

10¾

Mazatlan, Mexico . . . . . . . . . . . . . . .

9 40

7

. . .

A study of the preceding tables, with the aid of a map, will develop many interesting facts with regard to the propagation of the tide wave and the effect of the configuration of the coasts on the time and height of the tides. It will be seen, for example, that high water occurs nearly at the same time at the headlands of the great middle and eastern bays of the Atlantic coast of the United States - at Cape Hatteras, Nantucket island, and Cape Sable - making an allowance for the difference in local time. If by a line on the map we connect these points at which high water occurs simultaneously, we may regard that line as representing the crest of a tide wave advancing upon the coast. We shall find high water to occur later and later as we go up into the hays and rivers; and by following up the progress of the waves, we may be enabled to draw lines representing the time of high water or the top of the wave for each successive hour. Such lines are called co-tidal lines, and have been traced for the coasts of the United States by Prof. Bache, for which we again refer to the coast survey reports.

A chart of co-tidal lines for the British isles, by Prof. Whewell, will be found in Keith Johnston's "Physical Atlas," as well as a chart of co-tidal lines for the whole globe; but the latter must be looked upon as a rather adventurous generalization, in the absence of any positive knowledge of the tides in mid-ocean. The tides about the British isles present a very interesting study. The advancing high water passes up the English channel, occupying six hours from the Scilly isles to the mouth of the Thames, where it is met and reenforced by the high water 12 hours older, which has travelled around the isles to the northward and down the North sea. There is a point in the latter, about midway between Yarmouth and the Texel, where the co-tidal line of nine hours of the latter tide wave intersects that of three hours of the former, causing the interference of low water of the one with high water of the other tide, in consequence of which no change takes place in the sea level, as has been ascertained by actual observations over a shoal spot in that locality.

A remarkable case of the meeting of two tides, which will be more particularly noticed below, occurs near Throg's Neck at the W. end of Long Island sound. - The agency of tidal currents in producing changes in the entrances of bays and harbors is a subject of the first importance to commerce and navigation, which has received full attention in the prosecution of the American coast survey. As on the average the same amount of water moves inward and outward with the flood and ebb tides, we might readily suppose that the same amount of material is transported either way, and that no important change would take place in the configuration of the bottom. But the operation of the flood stream is very different from that of the ebb stream. We have as a general feature an interior basin of some extent communicating with the sea by a comparatively narrow passage. The flood stream, therefore, running with considerable velocity through this channel, will as it enters the basin spread out and become slow, depositing the sand and mud it is charged with, and making extensive flats or shoals opposite the entrance.

The ebb stream runs slowly over the flats from all directions toward the opening without removing much of the deposit, and gradually concentrates in definite narrow channels, which it scoops out, and the depth of which will depend in a great degree on the proportion of the area of the basin to the outlet, or, in other terms, on the difference of level which will be reached during the ebb between the basin and the ocean, which determines the greatest velocity and transporting power reached by the ebb stream. On the bars of most of the sand-barred harbors on our southern coast, the place and direction of the channel are frequently changed during violent storms, when the direction of the waves happens to be oblique to that of the channel; or when the sea runs directly upon the channel, the depth of water may be considerably diminished for the time being, by the sand rolled up by the waves. But in all these cases it is found that the normal depth is speedily restored by the scour of the ebb tide, which depends upon the unchanged factors of area and form of basin, height of tide, and character of the material forming the bar. To illustrate the important subject of tidal currents, we will examine the hydraulic system of New York harbor.

Considering first the progress of the tide wave through Long Island sound from the eastward to its meeting with that entering New York bay at Sandy Hook, we see that about 7½ hours after the transit of the moon high water has advanced just within Block island with an elevation of 2 ft., and at the same time has just passed Sandy Hook with an elevation of 4½ ft. Traversing the sound westward with increasing heights, it reaches Sand's Point three hours later with a height of 7.7 ft. The observed time of transmission from the Race to Sand's Point is 2h. lm., and the time computed from the depths according to the law developed by Airy is 2h. 14m.; a very good approximation when we consider the irregularities in the configuration of the sound, which could not bo taken into account. Advancing still further, the height somewhat declines in consequence of the changes of direction in the channel and its shallowness. At Hell Gate this tide wave is met by that which had entered at Sandy Hook, and advanced more slowly owing to the narrowness and intricacies of the channel, especially in the East river.

These two tides which meet and overlap each other at Hell Gate, differing in times and heights, cause contrasts of water elevations between the sound and harbor which call into existence the violent currents that traverse the East river. The conditions of the tidal circulation through Hell Gate are such that if there were a partition across it, the water would sometimes stand nearly 5 ft. higher, and at other times 5 ft. lower on the one side than on the other. In the actual case of the superposition or compounding of the two tides, the difference of level existing at any time is of course much less, but the difference of one foot is often observed within the space of 100 ft. in the most contracted portion of Hell Gate off Hal-lett's Point. The entrance from Long Island sound is a natural depression or arm of the sea which is not changed by the forces now in operation. The tidal currents which flow through it do not change the channel, but are obliged to follow it in its tortuous course. The Sandy Hook entrance, on the contrary, is characterized by a cordon of sands extending from Sandy Hook to Coney island, intersected by channels, which are maintained against the action of the sea, which tends to fill them up, by the scour of the ebb tide from the tidal basin of New York harbor.

The advance of Sandy Hook upon the main ship channel is among the notable and important instances of the effect of tidal currents; within a century it has increased a mile and a quarter. In the place where the beacon on the end of the Hook now stands there was 40 ft. of water 15 years before it was built. The cause of this growth is a remarkable northwardly current along both shores of the Hook, running both during the flood and the ebb tides with varying rates, and resulting from those tides directly and indirectly. The best water over the bar is about 2 m. E. of Sandy Hook light, in a direct line with the Swash channel; the greatest depth over it is 22 ft. at mean low water, and the same depth can now be carried through the Swash channel, which formerly was 3 ft. shallower, but has deepened since the cross section between the Hook and Flynn's knoll has been diminished by one third its area by the growth of the Hook. This relative change in the capacity of the channels has not affected the depth on the outer bar, which, according to the principles above laid down, is dependent mainly upon the area of the tidal basin within.

The depth of 22 ft. at mean low water, which is now maintained at the entrance, through the sands constantly thrown up by the waves of the sea, may be considered as depending upon the following elements: 1, the large basin between Sandy Hook and Staten island, including Raritan bay, which furnishes more than one half of the whole ebb scour; 2, what is called the Upper bay, including the Jersey flats and Newark bay; 3, the North river, perhaps as far as Dobbs Ferry, maintaining the head of the ebb current, although not directly taking-part in the outflow; and 4, a portion of the sound tide, which flows in through Hell Gate. The proportion of the first three divisions in producing the depth of channel may be approximately estimated by a comparison of the areas and distances from the bar. In order to maintain the depth which we now have, it is important that the area of the tidal basin should not be encroached upon. In proportion as that is diminished the depth of the channels will decrease. The flats, just bare at low water, but covered at high tide, form as important a part as any other portion, for it is obvious that it is only the volume of water contained between the planes of low and high water, the "tide prism," that does the work in scouring the channels.

The water on the flats is especially useful by retarding the outflow, thus allowing a greater difference of level to be reached between the basin and the ocean. The part which the fourth division in our classification of the basin of New York, that of the East river and Hell Gate passage, plays in the outflow of the ebb tide through the Sandy Hook channels, depends less upon the area involved than upon the difference in point of time and height of tide in Hell Gate already adverted to. The westerly current, usually called the ebb stream since it falls in with the ebb stream of New York harbor, taking place when the sound tide is highest, starts from a level 3½ ft. higher than the easterly, and thus a much larger amount of water flows out through the Sandy Hook channels than through the narrows at Throg's Neck. It is apparent, then, that this portion of the ebb stream, reenfor-cing the ebb stream of the harbor proper at the most favorable times, performs a most important part in maintaining the channels through the Sandy Hook bar.