TIDES AND CURRENTS 



The upper curve is the larger side, and shows how it 

 diminishes at the first and third quarters (end of line to 

 the left) and increases at new and full (to right). The 

 lower curve is the smaller tide, and it is almost uniform 

 through all phases of the moon, though it is not always 

 so uniform as in the portion figured. 



Seiches. — The tide record shows what is known as a 

 " festooning," due to lesser undulations. These are seen 

 chiefly during blizzards, but they are known to occur also 

 in calms. The small scale on which the record is made 

 prevents any analysis of these undulations, but they were 

 more clearly seen on the first tide-measuring instrument 

 which we used. Before the recording tide-guage was de- 

 vised Dr. Mackay built an instrument for measuring tides. 

 In this there was simply a weight sliding on an inclined 

 plane which was marked as a scale. A pencil working in 

 a straight Hne gave the amount of the tides, but to get 

 the time of the different phases it had to be observed at 

 regular intervals. It was noticed that over and above the 

 steady rise and fall of the tide, the weight was constantly 

 rising and falling at intervals of one or a few minutes, 

 and sometimes to the extent of four inches or more. 



It would have been possible to plot a detailed curve 

 of these oscillations by observing at intervals of half or 

 quarter minutes, but the cold was too great to permit 

 uncovering the hands to record the observations. These 

 oscillations are considered to be of the nature of seiche 

 waves. Seiche was the name given to certain free oscilla- 

 tions of enclosed bodies of water, first observed in Swiss 

 lakes by Professor Forel. Whatever the origin of the 

 inequalities of level which must precede the oscillation, 

 that continues as a seiche, diminishing till a state of rest 

 is again reached. 



The period of the seiche (i.e., the time between the 

 recurrences of the same phase of the oscillation) has a 



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