Theory of the Tides 



295 



equation (IX. 19) changes only insofar as H is replaced by 7/cos 2 and 

 p = (nR/c)coS(p. 



For a series of zonal canals which can be imagined to exist in the oceans 

 between the continents, Prufer (1936) and Dietrich (1944) have computed 

 the distribution of heights and phases along these canals for the M 2 and 

 the K x tide. An example is given in Table 32; it refers to the transverse 

 oscillation in a zonal canal of the Atlantic Ocean at 10°S. latitude. The forced 



Table 32. Forced transverse oscillation of the Atlantic at 10°<S. Lat., 



S5°W-13°E. long, (between South America and Africa) 



(Depth = 4-52 km. Phase referred to Greenwich) 



transverse oscillations of a semi-diurnal and diurnal character have in the 

 entire Atlantic Ocean (with the exception of 30°N. for the semi-diurnal, where 

 the ocean has its largest zonal extension) one "pseudo" nodal line, at which 

 the amplitude is reduced to a minimum and the phase changes by about 1 80° 

 over a short distance. In the Pacific Ocean, the number of nodal lines increases 

 when going from the pole towards the equator. For M 2 there is one nodal 

 line at 50°N„ two in 40° and 30°N., three in the equatorial sections. In the 

 Southern Pacific Ocean there are two nodal lines, when the Tasman Sea and 

 the Coral Sea are excluded. In the Indian Ocean, the M 2 tide shows a nodal 

 line for a canal at 5°N., and two for canals at 10° and 30°S. The /^-tide, 

 in the Indian Ocean, as well as in the Pacific, has only one nodal line in each 

 zone; only in the latter are there two nodal lines at 10°N. in the region of 

 the largest zonal extension. 



These computations are supposed to give only indications as to the ap- 

 proximate behaviour of these oceans in respect to the oscillation in a west- 

 east direction. It is obvious that transverse motions may alter essentially the 

 actual tidal picture resulting from the tide-generating forces, and, as we have 

 seen, there will be a development of amphidromies. However, there will be 

 little change in the number and position of the nodal lines, which become 

 nodal points through the development of amphidromies. Thus, the canal 

 theory of Airy also contributes towards a better comprehension of the 

 ocean tides. 



