ON THE COASTS OF IRELAND. 121 



From these circumstances it is plain that the time of high water (confining our 

 remarks to the term C^ sin (p+Cj)) respects mainly the time of the sun's transit and 

 not that of the moon's transit ; and therefore, at Courtown, the solar tide is greater 

 than the lunar tide. This is, I believe, the only place on the earth in which such a 

 result has been distinctly obtained. The observations of Sir Edward Belcher* show 

 that at Otaheite the solar tide is as nearly as possible equal to the lunar tide. 



The times following lunar syzygy by two days were June 24, 9\ July 9, 19^, July 

 23, 23^ August 8, 4^ August 22, 16^^; and about these times the luni-solar tide is 

 greatest at all the other stations. About these times also the soli-lunar tide at Cour- 

 town is greatest. 



The solar hour of high water at Kingstown, at the highest tides, is about 12'' 30", 

 that at Dunmore East is about 6'' 40"*. These are the two stations nearest to Cour- 

 town on the north and south sides. The solar hour of high water at Courtown at the 

 same times is about 9'* 30'". At these times the effects of the sun and the moon are 

 simultaneous as to phase, so that we may treat the result as if there were only a single 

 wave. It would seem then that the transition from a tide of elevation at Dunmore 

 East to one of simultaneous depression at Kingstown, and vice versa, is not effected 

 entirely by a node dividing the elevated wave from the depressed wave. It appears 

 that there is also a small progressive wave. The geometrical representation appears 

 to be this ; that there is a large stationary wave, having a node near Courtown, and 

 making high water simultaneous in all parts of the inland sea or Irish Sea, and syn- 

 chronic with low water in the exterior sea ; and that there is mingled with it a very 

 small progressive wave. As to the mechanical explanation of it, I can offer nothing 

 positive. But I would suggest for the consideration of wave-theorists, whether, in 

 the case of a gulf (as the Irish Sea) having a small outlet (like the North Channel), 

 it be possible that tiie fluctuation may be represented correctly on mechanical prin- 

 ciples by a combination of the stationary wave peculiar to a gulf with the progressive 

 wave peculiar to the channel. 



Returning now to the consideration of the magnitude of the tide, it is evident that 

 the coefficient of the lunar tide has been diminished in a far greater degree than that 

 of the solar tide. There is one explanation of this which is very plausible, and which 

 I have no doubt is the true one, namely that the node for the lunar tide and the 

 node for the solar tide do not coincide (which, on account of the difference of the 

 pei'iods of these tides, we should expect a priori), and that the node for the lunar 

 tide is much nearer to Courtown than is the node for the solar tide. It is clearly 

 possible that, by varying our choice of stations, we might vary the proportion of the 

 two effects in any degree whatever. Nay, by choosing a station between the two 

 nodes, we might have the solar and lunar effects to conspire when they are opposed 

 at other places, and vice versa ; and thus a station would be found where the spring 

 tides occur at the same time as neap tides at other places. This does not occur at 



* Philosophical Transactions, 1843, p. 55, &c. 



MDCCCXLV. R 



