12 



S. Xakamura aad K. Honda 



the intervals taken are large, the result will be a simple sinusoid. 

 Practically we found that eight or sixteen intervals are sufficient 

 for the purpose. The number of intervals need not, of course, be 

 equal to 2". T; hut the graphical method of drawing the mean 

 curve as above explained is practically more convenient than any 

 analytical method, taking an arbitrary number of intervals. In 

 Fig. G, tlie curve G a is a limnogram obtained at Hakoné, and the 

 curves drawn in full lines in G h and G c are the curves obtained 

 by the above method for seiches of periods of 15.4 and 6.7 minutes 

 respectively, by taking for G h eight, and for G c sixteen, intervals. 

 The result is simple sinusoids, and we can see their amplitudes 



Hikoné, Lake Biwa, Sept. 18, 1901. 



Fig. 7 a. 

 T=30.'"3 



Fig. 7 b. 

 T=16y>5 



and j)hases clearly from the figure. The curves in Figs. 7 «, 1 h 

 are similar one obtained at Hikoné on lake Biwa. This method 

 serves also to verify the existence of any motion in a limnogram, 

 for when the motion in question is not present, the mean curve 

 comes out practically a straight line. 



:t. l-^xperiinenfs with models. 



In order to study several possible modes of oscillation in a 



