Harmonic Analysis oc Tidal Obserrations. Q 



smootli running and good order. He records the comparison of 

 the clock indication with the correct time. The height of the wa- 

 ter is read from the tide-staff in order to obtain the working scale 

 of the instrument. 



Besides these duties, he observes the temperature of the 

 atmosphere and the sea- water, and estimates the strength of the 

 wind and its direction, when he visits the observatory. 



The sheet is changed once in every ten days and the clerk 

 draws on it the time lines at which he visited the observatory. 

 The marigrams so preparad, with the other records and necessary 

 remarks, are sent in to the Land Survey Department every tenth 

 day. 



Height of the Zero-Point of the Instruments. 



The precise levelling in our country is carried on by the Land 

 Survey Department of the Army, by comparing the heights of all 

 the survey points with the fundamental datum in the garden of the 

 Department. The height of the datum is referred to the mean 

 sea-level observed in the Bay of Tokyo and the value adopted at 

 present is 24.500 metres. 



The heights of all the bench-marks about the tide observa- 

 tories are referred to the mean sea-level of the Bay of Tokyo by 

 means of successive comparisons with the datum at the Land 

 Survey Department. The height of the instrumental zero-point is 

 determined from the comparison of it with that of the bench-mark. 

 Thus, in order to know the heights of the zero-points, referred to 

 the mean sea-level of the Bay of Tok3'-o, we gathered the necessary 

 constants for all the stations, as in the following table. There Hi 

 represents the height of the bench-mark referred to the mean sea- 

 level of the Bay of Tokyo; Hg the height of the zero-point of the 



