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Mr. T. Wright, Harmonic Tidal Constants [Aug. 1 , 



G. H. Darwin for the loan of the apparatus he devised to facilitate 

 the summation of hourly tidal heights, and to the Hydrographer, Admi- 

 ral Sir W. J. L. Wharton, who supplied me with the observations. 

 The whole of the observations w T ere reduced by the methods devised 

 by Professor G, H. Darwin.* 



The observations made at the three first- mentioned ports were 

 derived from copies of continuous diagrams made by automatic tide 

 gauges; those at Brisbane and Sydney were times and heights of 

 high and low water. The observations in every case extended over a 

 period of about 1 year, and were almost complete. The breaks in the 

 continuity of the observations were so short that approximate values 

 could be easily inserted by interpolation with very small risk of error. 



From the automatic records at Ballina, Princess Eoyal Harbour, 

 and Newcastle the hourly heights were read off to the nearest one-tenth 

 of a foot, The range of the tide at these ports is small, and an 

 attempt was made to use a smaller unit, one-twentieth of a foot. An 

 experiment with one month's observations showed, however, that the 

 hourly and daily sums for the month differed very slightly, whether 

 the readings were taken to the nearest one-twentieth foot or to the 

 nearest one-tenth foot only. Besides, when the diagrams for two con- 

 secutive days were placed end to end there frequently appeared to be 

 a difference of at least one-twentieth of a foot between the end of one 

 day's curve and the beginning of the next day's. For these reasons it 

 was considered to be sufficient to work to the nearest one-tenth of a 

 foot, and that length was adopted as the unit. 



The heights being read off, the method followed was exactly that 

 described by Professor Darwin, except in one detail. The S sheet 

 (that is, the sheet which is used for obtaining the hourly sums for the 

 S tides) was not used. These sums were made on the sheets on which 

 the hourly heights were entered from the diagrams. As in Professor 

 Darwin's method, the hourly sums were made in groups of days which 

 could be built up into the 30-days' period for the S tides and into the 

 7 4-day s' period for the other tides. The daily sums were made through- 

 out the year (they are required for the long-period tides). By forming- 

 totals of these daily and hourly sums in appropriate groups they act as 

 a check on each other, and the two sets of sums are settled. 



The hourly heights for the first 74 days were then entered on the 

 strips, the strips were pinned to the M sheet, and the additions made. 

 The total of the 48 sums was checked against a corresponding total 

 made up from the daily sums and the hourly sums for S. Agreement 

 among these three totals is a check upon the copying on to the strips, 

 and also upon the sums for M. This slight modification of forming 

 the sums for S from the original heights as read off from the diagrams 

 saves one shifting of the strips, and, if all goes well and the totals 

 * 'Koy. Soc. Proc.,' vol. 48, pp. 277—340, and vol. 52, pp. 345—389. 



