102 Messrs. K. Honda, T. Terada, and D. Isitani on the 
gular tank (150 x 76 x 1 9 cm. 3 ) filled with water to the water- 
line of the model. 
The waves were then excited by a pendulum-bob oscillating 
in the water. This was a lead ball, 7 cm. in diameter, 
suspended at the end of two pieces of cord, which from the 
point of suspension above passed downward through two 
holes in a movable horizontal bar, the latter being used to 
regulate the effective length of the pendulum. The part of 
the pendulum which oscillated with the bob was thus re- 
stricted to that part of the strings below the horizontal rod, 
the length of which could be varied at will by moving the 
rod upward and downward. With the pendulum arrange- 
ment, it was easy to obtain a period less than three seconds, 
but if one wished to obtain a longer period it would be 
necessary to use a pendulum of a considerable length. To 
avoid this inconvenience a horizontal pendulum was utilized. 
This was constructed by taking a horizontal brass bar, the 
one end of which rested in a steel cup embedded in a vertical 
framework, while the other was held by a cord which sloped 
from a point at the top of this framework. The cord was 
here attached by means of a steel ring, which rested on a 
knife-edge. A heavy lead ball was then suspended on the 
end of three strings from a frame attached to the movable 
end of the horizontal rod. By properly inclining this vertical 
framework, periods larger than three seconds could easily 
be obtained. 
When the pendulum was made to oscillate in front of the 
model with its bob under the surface of the water, the water 
in the model oscillated smoothly, with no appreciable surface 
waves. In order to keep the amplitude of pendulum oscil- 
lation constant, a slight force by hand was applied near the 
upper end of the pendulum at suitable intervals. To avoid 
the reflexion of the excited wave from the walls of the tank, 
a thick layer of a damping material, such as wood-shavings, 
was laid in front of the reflecting walls. 
By simply exciting waves with the above arrangement, 
the water in the model made a standing oscillation, whose 
amplitude was generally small ; but as the period of the 
pendulum approached to the proper period of the bay, the 
amplitude of oscillation gradually increased ; and when 
the period of the pendulum coincided with this proper period, 
its amplitude was a maximum. In this case the mode of 
oscillation was the same as that conceived bv us, that is, the 
end of the bay was a loop for the vertical motion, and a 
node for horizontal motion ; while its mouth was a node 
for vertical motion, and a loop for horizontal motion. The 
