122 



MR. AIRY ON THE LAWS OF THE TIDES 



Courtown ; but the reader, in reflecting on this, will see the importance of our com- 

 parison of the time of the largest tides at Courtown with the time of the largest tides 

 at the other stations. 



We shall now proceed to examine the second periodical term ; which will be found 

 not less remarkable than the first. 



On glancing over the values of c^ (first correcting that on August 9 as I have sug- 

 gested), the reader cannot fail to be struck with the general uniformity of the num- 

 bei*s. It is quite evident that this term has no respect to the sun's transit, but that 

 it respects only the moon's transit, or the commencement of the luni-solar tide. If 

 we look also to the coefficient C^, we find that its magnitude is considerable, some- 

 times exceeding that of the first term. It is clear therefore that this term does not 

 originate as a derivative from the first term, produced by the local circumstances of 

 the port. It does not change greatly, but nevertheless has on the whole larger values 

 about the times of large tides than about the times of small tides. If we divide the 

 observations into two groups, one corresponding to large tides and the other to small 

 tides (the limits being the same as those for the other stations) ; and if we correct as 

 before for the establishment at Ardglass (to which station the Courtown tides have 

 been referred) ; and if we collect the expressions for the second periodic term at the 

 three stations, Dunmore East, Courtown and Kingstown ; we have this sequence of 

 expressions. 



It appeal's here quite evident that this term at Courtown is only the representation 

 of the same quarto-diurnal tide which shows itself along the whole coast. This wave 

 (whatever its origin may be) appears to have its greatest range and its beginning of 

 phases at Kingstown, and tospread both ways, diminishing in range as it goes. 



The succeeding terms at Courtown are insignificant. 



We have now a clear representation of the apparently confused phenomena of the 

 tides at Courtown. Both the semidiurnal tides are very much diminished, the lunar 

 so much that its range is rather less than that of the solar tide. The quarto-diurnal 

 tide exists in nearly its greatest magnitude. The geometrical representation is per- 

 fect ; the mechanical explanation is not complete. In both respects, as regards what 

 is reduced to law and what is yet incomplete, the Courtown tides must be regarded 

 as the most remarkable that have ever been examined. 



Section XVIII. — Exarmnation into the question of tertio-diurnal tide. 

 The observations at Courtown, as has been mentioned, and as appears from the 

 Table in pages 118 and 119, WQve continued without interruption, day and night, for 



