Harmonie Analysis of Tidal Observations. 



15 



The Working Scale of the Instrument. 



As we have already stated, the approximate scale of the in- 

 struments at the permanent, observatories is one-twentieth; but 

 the following exact values of the working scales were obtained by 

 the members of the Land Survey Department: — 



Takaw V^o.œ 



Kiirun Vso.o* 



Fukabori V20.08 



Hosojima Vso.os 



Tonoura Vso.oo 



Kushimoto Vso.n 



Wajima 



Aburatsubo 

 Iwasaki . . . 

 Ayukawa . . . 



Otaru 



Hanasaki... 



9.95 



/20.06 

 /20.11 

 /20.12 

 /20.41 

 /20.03 



Preparation of the Marigram for Reduction. 



The tide-gauges have pins round the drum both at the top and 

 the bottom. These pins, perforating the sheet, mark the beginning 

 of each hour and carry the sheet forward as the drum revolves. 

 The perforations thus made in the sheet are used as hour marks, 

 but as the clock rate is not uniform, the due correction is applied 

 to draw the hour lines. This preliminary operation being made, 

 the measurement of the height of the water is performed for each 

 hour. To ensure that the records are free from mistakes, the same 

 marigram was measured by two independent computers and their 

 readings were carefully compared together. When these agree 

 well within the error of measurement, one of them is taken for the 

 further reduction and the other is preserved for future reference. 

 Of course, in case one measurement differs too much from the other 

 the marigram is again measured to rectify the mistake of the read- 

 ing. For the measurement, a scale which is two decimetres long 



