52 K. HONDA, T. TERADA, Y. YOSHIDA, AND D. ISITANI. 



oscillating. By placing a photgraphic camera in a vertical posi- 

 tion over the model and exposing the dry plate about lialf a 

 period of oscillation, a fine path was traced on the plate by 

 each moving aluminium particle, and an aggregate of such tracks 

 of the particles showed beautifully the actual mode of the hori- 

 zontal motion. 



To determine the proper period of oscillation of a model, the 

 period of the pendulum was so adjusted as to give a nearly 

 maximum amplitude of resonance. The pendulum was then 

 stopped, and the period of the subsequent free oscillations was 

 determined by means of a stop-watch. Though the period of 

 the pendulum varied slightly from the proper value, the period 

 of the subsequent oscillation was quite constant. 



If the period of the exciter differed considerably from the 

 proper period of the bay, the oscillation after the stopping of 

 the pendulum was rapidly damped, and this gave us a good 

 means of detecting, whether the period of the exciter was near 

 to the proper one, or not. 



We experimented with models of seven bays, in which 

 regular and conspicuous undulations were observed ; the results 

 of experiments are given below : — 



(a) Bay of Hakodate. PI. LXXXVII. 



The scales of the model were as follows : — Length 1 : 20,200, 

 and depth 1 : 548, so that the factor r, which was to be multi- 

 plied into the observed period in order to obtain the period of 

 oscillation of the actual bay, was 863. The bay had two modes 

 of oscillation ; that is, the one was the fundamental oscillation 

 with its node at the mouth and the other tlie lateral oscillation 

 between Hakodate and Tomikawa with its node midway between 



