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December 12, 1844^. 

 The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" On the Laws of the Tides on the Coast of Ireland, as inferred 

 from an extensive series of observations made in connexion with the 

 Ordnance Survey of Ireland." By George Biddell Airy, Esq., F.R.S., 

 Astronomer Royal. 



The elaborate investigations of which the results are communi- 

 cated in the present paper, were suggested by the necessity of 

 adopting some standard mean height of the sea, as a line of refer- 

 ence for the elevations ascertained in the operations of the Ordnance 

 Survey of Ireland. Colonel Colby, R,E, who conducted that survey, 

 had Avith this view determined to institute a series of observations 

 on the height of the water in different states of the tide ; and con- 

 ceiving that these observations might be made subservient to im- 

 provement in the theory of the tides, requested the assistance of the 

 author in laying down the plan of observation best calculated to 

 effect that object. The suggestions which were, in consequence, 

 made by the author were adopted in their utmost extent by Colonel 

 Colby ; and the collection of observations was placed in the author's 

 hands in the winter of 1842. The whole number of observations 

 exceeds two hundred thousand ; and they derive extraordinary value 

 from the circumstance of the localities, of their simultaneity, their 

 extensive range, and the uniformity of plan on which they were con- 

 ducted. Their reduction was made by the computers at the Royal 

 Observatory, Greenwich, under the superintendence of the author, 

 and with the authority of the Lords Commissioners of the Treasury. 

 The nature of the different branches of the inquiry may be gathered 

 from the titles of the several sections into which the paper is divided, 

 and which are as follows : — 



Section I. — Account of the stations, levellings, times and methods 

 of observation. 



Section II. — Methods of extracting from the observations the 

 times of high and low water; of supplying deficient times and 

 heights ; and of correcting the times first determined. 



Section III. — Theory of .diurnal tide as related to observations 

 only ; and deduction of the principal results for diurnal tide given 

 immediately by these observations. 



Section IV. — Theory of diurnal tide as referred to the actions of 

 the sun and moon. 



Section V. — Discussion of the height of apparent mean water, as 

 deduced from the heights of high and low water only, corrected for 

 diurnal tide ; with reference to difference of station, and to variations 

 of the phase of the moon, and of the declination of the moon. 



Section VI. — Discussion of the range of the tide, and of semi- 

 menstrual inequality in height, apparent proportion of solar and 

 lunar effects as shown by heights, and age of tide as shown by 

 heights, from high water and from low water. 



Section VII. — Establishment of each port, and progress of semi- 

 diurnal tide round the island. 



