Lastly, there is the _storm wave_--the result of the cyclone or hurricane--and, perhaps, the greatest terror to seamen, for it almost always appears in the character of a _heavy cross sea_, the period of which is irregular and uncertain. The disturbance within the area of the cyclone is not confined to the air, but extends also to the ocean, producing first a rolling swell, which eventually culminates in a tremendous pyramidal sea and a series of storm waves, the undulations of which are propagated to an extraordinary distance, behind, before, and on each side of the storm field. Enough has now been said to show that whatever the character of the waves encountered by the Umbria and Martello in July last, they were in no sense "tidal," but, if approximating to the dimensions stated, they were either due to storm or earthquake, or, possibly, to a combination of both the last agents. For those of our readers who may be interested in wave observations, we conclude by introducing Prof. Stokes' summary of the method of observing the phenomenon: "_For a Ship at Sea._ "(1.) The apparent periodic time,[2] observed as if the ship were at rest. "(2.) The _true_ direction from which the waves come, also the ship's _true_ course and speed per hour. "(3.) A measure or estimate of the height of the waves. "(4.) The depth of the sea if it is known, but, at any rate, the position of the ship as near as possible, either by cross bearings of land or any other method, so that the depth may be got from charts or other sources. "_For a Ship at Anchor._ "(1.) The periodic time. "(2.) The true direction from which the waves come. "(3.) A measure or estimate of the height of the waves. "(4.) The depth of water where she is anchored." [Footnote 2: The period of a wave is the interval of time which elapses between the transits of two successive wave crests past a stationary floating body, the wave crest being the highest line along the ridge.] It is the opinion of scientists that when the period of oscillation of the ship and the period of the wave are nearly the same, the turning over of the ship is an approximate consequence, and thus the wave to such a ship would appear more formidable than to another ship with a different period of oscillation.--_Nautical Magazine._ * * * * * PRACTICAL EDUCATION.