50 



K. nONDA, T. TEEADA, Y. YOSHIDA, AND D. ISITANI. 



Fin:. G. 



the water ; a lead ball. 7 cm in diameter 

 was suspended by two strings passing 

 through two lioles in a horizontal rod, as 

 shown in Fig. 0. The joart of the pendulum, 

 which oscillated with the bob, was thus 

 restricted to that part of the strings below 

 the horizontal rod ; the length of this 

 portion could be varied at will by moving 

 the rod upward or downward. With this 

 arrangement, it was easy to obtain a 

 period less than three seconds. For a 

 longer period, however, it would be neces- 

 sary to use a pendulum of considerable 

 length. To avoid this inconvenience, a horizontal pendulum 

 was utilized. As shown in Fig. 7, a bar was horizontally sup- 

 ported by means of a string 

 suspended from a knife edge, 

 and of a steel cup, in which 

 the point of the horizontal 

 bar rested. A heavy lead 

 ball was hung by a three-way 

 string from a frame attached 

 to the horizontal rod. By 

 properly inchning the support 

 of the pendulum, periods 

 greater than tln-ee seconds 

 could easily be obtained. 

 When the pendulum was made to oscillate in front of the model 

 with its bob under the surface of water, the water in the model 

 oscillated smoothly with no appreciable surface wave. Though 



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