Depth of |            Length of the Wave in Feet.[1]
the Water|     |      |       |        |         |          |
in Feet. |  10 |  100 | 1,000 | 10,000 | 100,000 |1,000,000 |10,000,000
---------+-----+------+-------+--------+---------+----------

+----------
|
| Corresponding Velocity of Wave per Hour in Nautical Miles.
|
1 | 3.2 |  3.4 |   3.4 |    3.4 |     3.4 |      3.4 |       3.4
10 | 4.3 | 10.1 |  10.7 |   10.8 |    10.8 |     10.8 |      10.8
100 | 4.3 | 13.5 |  32.0 |   34.0 |    34.0 |     34.0 |      34.0
1,000 | 4.3 | 13.5 |  42.9 |  101.8 |   107.5 |    107.5 |     107.5
10,000 | 4.3 | 13.5 |  42.9 |  135.7 |   320.3 |    340.0 |     340.3
100,000 | 4.3 | 13.5 |  42.9 |  135.7 |   429.3 |   1013.0 |    1075.3
---------+-----+------+-------+--------+---------+----------

+----------

[Footnote 1:  As an example, this table shows that waves 1,000 feet
in length travel 43 nautical miles per hour in water 1,000 feet
deep.  The length is measured from crest to crest.]

From these numbers it appears that—­

1.  When the length of the wave is not greater than the depth of the water, the velocity of the wave depends (sensibly) only on its length, and is proportional to the square root of its length.

2.  When the length of the wave is not less than a thousand times the depth of the water, the velocity of the wave depends (sensibly) only on the depth, and is proportional to the square root of the depth.

It is, in fact, the same as the velocity which a free body would acquire by falling from rest under the action of gravity through a height equal to half the depth of the water.

Rollers are of the nature of a violent ground swell, and possibly the worst of them may be due to the propagation of an earthquake wave.  They come with little notice, and rarely last long.  All the small islands in the Mid-Atlantic experience them, and they are frequent on the African coast in the calm season.  They are also not unknown in the other oceans.  In discussing the meteorology of the equatorial district of the Atlantic, extending from lat. 20 deg. to 10 deg.  S, Captain Toynbee observes that “swells of the sea are not always caused by the prevailing wind of the neighborhood.  For instance, during the northern winter and spring months, northwesterly swells abound.  They are sometimes long and heavy, and extend to the most southern limit of the district.  Again, during the southern winter and spring months, southerly and southwesterly swells abound, extending at times to the most northern limit of the district.  They are frequently very heavy and long.”