SECONDARY UNDULATIONS OF OCEANIC TIDES. 8 / 



2^=126"\ which was actually recorded in the tide-gauge of 

 Batavia (PL XLIX, Fig. ?,f. Though the position of the node 

 at the southwest end is not very determinate, tlie ambiguity 

 does not affect tlie value of the calculated period in any serious 

 manner, because the bed to this end slopes down very steeply 

 toward the deep sea, so that if the virtual length of the strait 

 be assumed to be a little longer or shorter, tlie mean depth of 

 the oscillating basin becomes greater or less in a considerable 

 proportion, so that the value of //i/X remains fairly constant. 

 The fact that at Anjer at the northwest mouth of the strait, 

 the reported height of the waves was small, seems to stand in 

 liarmony with our supposition that the node lies near that place. 



Besides the mode of oscillation above described, a binodal 

 oscillation between the two sides of the strait, Java and Sumatra 

 sides, might possibly be generated by the eruption of Krakatoa, 

 wliicli lies at the loop of this mode of oscillation. The period 

 of the oscillation is calculated to be about one hour, wliicli 

 nearly coincides with the periods recorded at many stations 

 along the Indian coast. In addition, the higher modes of oscil- 

 lation than the above two with comparatively small amplitudes 

 might possibly have been in co- existence. 



Beyond tlie northeast end of the strait, the sea is shallow 

 and abounds in irregularities of bed, which may scatter the 

 weaves propagated from the end of the strait by complicated 

 reflection and refraction. Besides, the sectional area of the 

 northeast end of the strait is estimated to be about ^V that of 

 the southwest end, so that the energy j^ropagated from the 

 former mouth must liave been a small fraction of that from the 



*) All tide-gauge records regarding the Krakatoa eruption are the reproduction from the 

 Report of the Royal Society of London. 



