116 Messrs. K. Honda, T. Terada, and D. Isitani on tit 
le 
mode o£ oscillation possible in such a channel must lie midway 
through or perhaps somewhat nearer the narrower end. 
Fig-. 10. 
s*^ 
s. 
& 
f 1 *■ 7 J/iVA 
*«'+ 
***** 
Hence the eruption of Krakatoa which burst forth at the 
loop of this oscillation would be very favourable to excite 
natural, stationary oscillation of the strait as a whole. The 
initial disturbance would soon settle into a regular oscillation 
natural to the system, and this oscillation would be propa- 
gated into the external ocean as a train of regular waves, 
whose period is determined by that of the source. 
Taking the length o£ the strait as 160 km. and its mean 
depth as 183 m., we obtain from our formula * T = 126 m , 
which was actually recorded by the tide-gauge of Batavia. 
Besides the mode of oscillation above described, a binodal 
oscillation between the two sides of the strait, the Javan and 
Sumatra sides, might possibly be generated by the eruption, 
which occurred at the loop of this mode of oscillation also. 
The period of this oscillation is calculated to be about one hour, 
which nearly coincides with the periods recorded at man}- 
stations along the Indian coast. In addition, the modes o£ 
oscillation higher than the above two, with comparatively 
small amplitudes, might possibly have been in co-existence. 
Beyond the north-east end of the strait the sea becomes 
shallow and the bed abounds in irregularities, which may 
cause a scattering of the waves that have been propagated 
from the end of the strait, through complicated reflexion and 
refraction. Besides, the sectional area of the north-east end 
of the strait is estimated to be about -^ that of the south-west 
end; so that the energy propagated from the former mouth 
must have been a small fraction o£ that from the latter. These 
considerations probably account for the smallness of the waves 
propagated in the north-eastern direction. 
2/ 
* In this case, our formula evidently becomes T= -y— ; because both 
ends are open. ^ ( J' 1 
