DEDUCTIONS FROM THE TIDES. 29 



aflSrra that all the oceans behave, in the main, as if they were isolated bodies 

 held in basins on the surface of the lithosphere. There are no effective tidal 

 belts stretching around the earth parallel to the equator and furnishing an 

 opportunity for the development of a continuous tide of the canal type. 

 The Southern Ocean, once regarded as such, does not prove to act in this 

 way, nor do the Pacific and Indian Oceans act as a common body, as 

 represented on the old tidal charts.* For the purposes of this discussion it 

 may be assumed with practical safety that the seas occupy a chain of irregu- 

 lar basins linked to one another in various unsystematic manners, and that 

 each of these bodies is subject, in its own way, to such oscillations as the 

 rocking of its basin may impart to it. If the tides of the lithosphere are 

 as small as present evidence seems to indicate, this may not be important in 

 its own first effects, but as a periodic action it may become, by commen- 

 surate accumulation, a not unimportant factor. Some of the peculiar fea- 

 tures of the tides seem to be much more intelligible on the supposition that 

 they arise from the oscillations of the lithosphere than from the direct action 

 of the lunar and solar attractions. The rocking action of the basins would 

 generate tides as freely on the eastern as on the western sides of the oceans, 

 whereas the attraction of the moon and sun should be accumulative toward 

 the western side. The tides are, however, rather higher on the eastern than 

 on the western sides of the oceans. We shall have occasion to return to this 

 significant feature. 



When a strain, or a deformation, or a movement of any kind is being 

 impressed with increasing or declining intensity upon an elastic body which 

 is already in a state of constant pulsation, as is the lithosphere, the super- 

 imposed action becomes itself pulsatory, however continuous and uniform 

 the increment or decrement of the superimposed action may be in itself, 

 for the existing pulsation of the body alternately opposes and coincides 

 with the superimposed action and gives it a corresponding pulsation. The 

 water-tides assigned to the rocking of the containing basins may therefore 

 be treated as composite pulsations, each advancing and each declining 

 phase consisting of an undetermined number of pulsations, each of which 

 gives rise to its own partial free wave. These, as do all waves of what- 

 ever source, react on the lithosphere. Each such reacting pulsation, so 

 far as it takes the form of a compressional wave, passes through the litho- 

 sphere to the antipodes in about 22.5 minutes. It there constitutes an 

 impulse acting at an angular distance of about 5.6° in the rear of the corre- 

 sponding part of the antipodal wave, tending, in its minute degree, to 

 strengthen it, but with a slight increase of amplitude. The return of this 

 wave requires an equal period which brings it into action at about 11.2° 

 in the rear of the crest of the wave from which it sprang. This wave will 

 therefore act several times in an approximately commensurate way before 

 any appreciable incommensurate effects will be developed, and by that 

 time its force will largely be spent. In so far as the reaction of the original 

 wave develops an undulatory wave on the surface of the lithosphere, 

 this wave will reach the antipodes in about 2.25 hours and will act in a 



* See Tidal charts of the U. S. Coast and Geodetic Survey, Rept. Sept. 1900, App. 7, 

 Outlines of Tidal Theory, Pt. IV a, RoUin A. Harris. Also Pt. IV b, 1904. 



