SECONDARY UNDULATIONS OF OCEANIC TIDES. 21 



The large Bay of Miitsii has the form of a dumb-bell, con- 

 nected to the Strait of Tsugaru by a wide neck. The observa- 

 tion was made at Aomori, when the centre of a deep low 

 pressure was approaching the bay from Japan Sea side (PI. 

 XCIII). On this occasion, a regular undulation of 103™ appeared 

 on the record and continued for a day and a lialf. Upon this, 

 an undulation of the period ranging from 23.4"' to 26.3" was 

 superposed. Besides, a period of about 300™ may also be traced. 



The undulation of 103™ is probably the lateral oscillation of 

 the bay ; the period 108'" calculated on this view is in fair agree- 

 ment with the observed period. The undulation of the shortest 

 period may be its higher harmonics. The longest period is 

 perhaps that of the fundamental oscillation of tlie bay having 

 its node at the mouth ; tlie calcalation gives 284™ as the period 

 of this mode of oscillation. 



(2) Iwasaki. PI. IV, Fig. 3-4. 



Iwasaki is situated on a northern coast of Mutsu ; here 

 Kelvins' tide-gauge is constantly working. The undulation in 

 ordinary w^eather is generally conspicuous ; in stormy weather 

 (PI. IV, Fig. 3-4), undulations of considerable amplitude are 

 sometimes observed. The periods observed are 8.3™, 11.0™- 

 13.5™, 15.8™- 17.3™. 



(3) Niigata, Kashiwazaki, and Naoetsu (Aug. 9-17, 1904). 

 PI. V, Fig. 1-2. 



These stations are situated along the nortliern coast of 

 Echigo. The secondary undulation in these coasts are con- 

 spicuous, but much comphcated by the superposition of several 

 minor components. The periods observed are : 22.6™ at Niigata ; 

 11.6™-12.4™, 14.5™-17.2™, 22.0™-25.5™, 30.0™-35.8™ and 43.3™ at 

 Kashiwazaki ; and 37.6™ at Naoetsu. 



