Long Waves in Canals and Standing Waves in Closed Basins 191 



after the quadratures. The regular part of the Euripus currents, therefore, 

 is a consequence of the variety of the tides in the northern and southern 

 harbours of Khalkis. 



In both of these harbours there are always seiches. Contrary to the tides, 

 these seiches are of small amplitude in the northern harbour; Miaulis ob- 

 served during one month, despite stormy weather, only once amplitudes 

 of 15 cm during two oscillations; otherwise they were smaller than 5 cm. 

 The seiches in the southern harbour are a daily occurrence and have greater 

 amplitudes. The period of the seiches for Khalkis north is 1 -44 h, for Khalkis 

 south 1 84 h. The Japanese method (p. 164) was used to explain the period 

 of these seiches. It gave for the Evrippon Euripus (node at the opening near 

 the Isle of Kavalianis) 1 -87 h, in accordance with the observations. The 

 regularly shaped bay, the narrowing near the opening and the funnel-shape 

 of the adjoining Gulf of Petali call for greater amplitudes, as it was observed. 

 The period of the free oscillations of the entire northern canal with a correc- 

 tion for the opening is 6-49 h for the uni-nodal wave and 104h for the two- 

 nodal wave. It is doubtful, considering the complicated form of the northern 

 canal, whether such oscillations occur. They have not been observed. It is 

 possible that the 1 -44 h seiche is the one of the Talantic Euripus combined 

 with the seiche of the Mali Gulf, with an opening in the Oreos channel. If we 

 consider this as a closed system, the period of the free oscillation will be 

 96 h, hence smaller than the observed period of l-44h. With this disagree- 

 ment it can be expected that the amplitudes of the seiches in the northern 

 harbour, if there are any at all, will be small. Since in the southern harbour 

 the amplitude of the tide is small, the seiches become especially important 

 for the Euripus currents. According to their period, they can, under certain 

 circumstances, cause the current to alternate fourteen times in the course 

 of 24 h in the narrows of Khalkis. If we consider these irregular currents as 

 the actual Euripus problem, then Forel, in referring to the seiches, was the 

 first to give a correct explanation. 



A close scrutiny of the differences in the level in the northern and southern 

 harbours of Khalkis permits to get a better insight into the phenomena of 

 the reversal of the currents. Endros concluded from the observations of 

 Miaulis that these currents are not horizontal displacements, like in the 

 vicinity of the nodes in standing waves, but a compensating gradient current. 

 The reversal in the direction of the current occurs simultaneously with the 

 change of sign of the difference in level, and not at the time of extreme levels 

 in the north and the south of the narrows, as would happen in the case of 

 the water-masses oscillating through the narrows. The number of changes 

 in the direction of the current during one day depends also, however, on the 

 general daily level in the entire area of the Euripus. These variations in level 

 are superimposed on the tidal and seiches currents and they fix the sequence 

 of the changes in the current. The variations of the daily mean level originates 



