Transactions of the Royal Society of New Zealand . there is a closer agreement between thevelocities (values of VJ for paths calculated along the chord than for thosecalculated along the arc ; in otherwords, that the chords represent acloser approximation to the actualpaths than the arcs. (It will beunderstood that the chord cannot bethe actual path of a wave passingthrough layers of varying density,and subject, therefore, to refractionat the bounding surfaces.) It will be seen that the velocity(Pj) of waves, calculated along thechord, for places not more than 60°from the origin is about 760 k
Transactions of the Royal Society of New Zealand . there is a closer agreement between thevelocities (values of VJ for paths calculated along the chord than for thosecalculated along the arc ; in otherwords, that the chords represent acloser approximation to the actualpaths than the arcs. (It will beunderstood that the chord cannot bethe actual path of a wave passingthrough layers of varying density,and subject, therefore, to refractionat the bounding surfaces.) It will be seen that the velocity(Pj) of waves, calculated along thechord, for places not more than 60°from the origin is about 760 kilo-metres, per minute ; that for placesbetween about 60° and 90° from theorigin the chordal velocity isgreater ; that for distances over 90°it is considerably less. This enables us to formulate ahypothesis illustrated by the dia-gram (fig. 2). Disregarding the sur-face rocks, which I have elsewhere shown to be not more than twenty-five to thirty miles in thickness, wemay assume a shell of much greater density about 500 miles in depth (AAA.). Fig. 2. Possible Paths of Py Waves, 9th November,1910, to Wellington, OW; Perth, OP:Zikawei, OZ ; Victoria (), OV; , 111, or 222, or 3r 3. O, origin. 142 Transactions. and below that a shell of still greater density about 630 miles thick (BBB).Below the last-named shell there seems to be a marked change of physicalcondition—either the density is much less (which is hardly conceivable) orthe centrosphere (CCC) is viscous. I have drawn hypothetically the possiblepaths of preliminary waves reaching the San Fernando Observatory from theorigin : (a) They may have been transmitted along a path approximatingto the chord 111, but with greatly reduced speed through the centralportion ; or (b) they may have been transmitted along, or nearly along,the path 2 2 2, as internal surface waves for the middle portion of thepath—that is, along the surface of the centrosphere ; or (c) they may havebeen transmitted along a path 3 r
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