DEDUCTIONS FROM THE TIDES. 31 



something less than 3.5" i)er century, whilst the length of the day may remain almost 

 unaffected. 



The results of these two hypotheses (a viscous spheroid and a nearly perfectly elastic 

 spheroid) show what fundamentally different interpretations may be put to the phenom- 

 enon of the secular acceleration of the moon. 



Under these circumstances, I can not think that any estimate having any pretension 

 to accuracy can be made as to the present rate of tidal friction.' 



THE TIDES OF THE HYDROSPHERE. 



If the preceding views are tenable, practically the whole tidal effect 

 on rotation at present is concentrated in the water-tides. A part of these 

 are assigned to the immediate action of lunar and solar attraction and a 

 part to the mediate action of the lithosphere. While the lithosphere is 

 thus supposed to contribute to the formation of the water-tides, this sup- 

 plementary action is supposed to be qualified by its distributive action 

 as previously explained. The water-tides are thus interpreted as more 

 complex in origin than they have usually been thought to be. This must 

 doubtless be regarded as an unwelcome infliction, for even under the simpler 

 conception of their origin from direct attraction only, they are, in many 

 of their phases, beyond complete mathematical treatment. These added 

 complexities put them still further beyond the reach of such treatment. 

 But this added complexity may, after all, only help to force us on toward 

 the adoption of naturalistic methods. It has been becoming increasingly 

 clear for some time that, to secure reliable results, the tides must be studied 

 on a direct observational basis. The more hopeless the purely theoretical 

 method becomes, the more assiduously is the observational method likely to 

 be pursued. If theoretical methods are given precedence, they should be such 

 as are based on the fundamental laws of energy, which hold good irrespective 

 of special forms of action, however multitudinous and irresolvable. 



As already remarked, the tidal water-bodies have no systematic, much 

 less have they any symmetric, distribution. Innumerable idealizations 

 as to the forms and relations of the oceans have been framed, but beyond 

 a few of a very general sort, they are notable principally for their undue 

 emphasis of amenable concurrences and their neglect of refractory non- 

 concurrences. The north-south extensions of both the eastern and western 

 continents are particularly unfavorable for the development of a con- 

 tinuous forward movement of the tides. The southern ocean furnishes 

 the only continuous east-west belt of ocean encircling the earth's axis of 

 rotation, but, according to the cotidal charts of the U. S. Coast and Geo- 

 detic Survey, this is not affected by a continuous westerly tide. The 

 Pacific tides move easterly from New Zealand and, by interpretation of 

 the scant data available, easterly all the way to the straits between South 

 America and Antarctica, through which they move eastward and then 

 northward along the Patagonian coast. The tides of the northeastern part 

 of the Indian Ocean move easterly into the straits between Australia and 

 Asia, while the Pacific tides enter on the opposite side and the two sets 



» On the precession of a viscous spheroid, etc. <Phil. Trans. Roy. Soc. Lond., Ft. II, 

 1879 (1880), p. 529. 



