vi PREFACE. 



responds to waves of different periods, so that they are mingled 

 together, this procedure was the easiest step for analysing the 

 different components. 



Dr. Endrös, in his elegant research on the seiches in one 

 of the Bavarian lakes, made nse of a model for studying the 

 periods of oscillation. The same method was follow^ed by Drs. 

 Honda, Terada, and Isitani in a slightly different manner. The 

 models of bays having the contour lines and the magnified 

 depths of those already studied wei-e placed in a water tank, 

 so that tlie water in the model came to the level mark, and 

 waves were then excited in the tank. When the period of the 

 wave was in harmony with that of the model bay, the water in 

 the model responded to the exciting wave with extreme ease, and 

 continued vibrating for some time even after the subsidence of 

 the exciting wave. Not only was Dr. Endrös's experiment ex- 

 tended in this direction, but the courses of the stream Hues in 

 the model were closely studied by Dr. Honda. By an ingenious 

 device of sprinkling the surface of water with fine aluminium 

 powder, and photographing the surface by a camera with the 

 optical axis vertical, the trace of dust particles was observed ; 

 these photographs proved distinctly that the surface of the 

 water was oscillating and showed at a glance the mode of 

 response to the external source of excitement. This graphical 

 representation is more practical than that deduced from mathe- 

 matical calculation, which is next to impossible on account of 

 the variable deptli and tlie irregular contour. Thus in delineating 

 the oscillations proper to bays^ the study with models, when a 

 hydrographical chart can be obtained, is generally sufficient to 

 determine the nature of oscillations and their periods. It seldom 

 happened that the periods which can not be detected with the 



