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XX. 
ON THE HARMONIC TIDAL CONSTITUENTS OF THE POET 
OF DUBLIN. By SIR ROBERT S. BALL, Royal Astronomer 
of Ireland. 
[Read December 10, 1888.] 
In the recent edition of the Admiralty Manual of Scientific Inquirj^, 
Professor G. H. Darwin has described and illustrated by an example a 
convenient method of determining the chief Harmonic Tidal Consti- 
tuents, from a series of observations of the height (}i the water taken 
every hour for 720 consecutive hours. For the explanation of the 
process, reference must be made to the work referred to. 
As an exercise in this method, I have investigated the tides in our 
own. port. By the kindness of the Secretary of the Port and Docks 
Board, and of their Engineer, Mr. Stoney, and his assistant, Mr. 
Griffith, I was permitted to have access to the admirable series of 
automatic tidal records which have been taken at the North Wall for 
many years. I selected for my purpose the observations made in May 
and June, 1887. 
The first operation was to read off from the curves traced by the 
machine the height of the water at each hour for 720 consecutive 
hours. As the epoch for commencing, I took noon, on May 28th, 1887, 
when the height of the water was 7*4 feet. The results of the read- 
ing are shown on the sheet S, where, for convenience, I have omitted 
the decimal points. For example, on the 13th June, at 17^ we find 
the figures 106. This means that at 5 a.m. on the 14th June, in civil 
time, the tide-gauge showed the water stood at 10*6 feet above a cer- 
tain arbitrary level taken as the zero. Allowance has been made for 
barometric pressure at the rate of a foot of height per inch of mercury. 
The standard I took was 30 inches ; but this is immaterial. 
