Diurnal Tides of the Coasts of Ireland. 57 



and consequently, by equation (3), 



y = — cot (m — i,n) . 

 Substituting for h and / their values, we find 



^11^ = cot (m-4) = cot (45° 6') ; 

 0-1726 ^ 



and, converting 45° 6' into time, we have 



m-i,n = ^^ Q"^ ', 



but m, which is the establishment at Castletown send expressed 



in local time, is equal to 4^ 17"", and therefore 



Equation (4) also gives us the relation 



2M sin (3 max. declination) = Vh^ + P. 



Hence 



2M=^^^ = ^ =0-363 feet. 

 "^^^ sin (42°) 0-669 



If, therefore, the diurnal tide at Castletownsend be supposed 

 wholly due to the moon, it may be expressed by the formula 

 D = 0-181 sin 2/iC0s(m-l^ 11™). 

 In this equation, /a, the moon's declination, is to be assumed 

 for a period preceding the time of observation. The length of 

 this period or age of the tide could not be ascertamed in conse- 

 quence of the irregularity of the times of vanishing. It appears 

 from the preceding investigation, that the maxmmm effect in 

 raising or lowering the sea produced by the diurnal tide at 

 Castletownsend is 



0-181 ft. X sin42°=0-117ft. =1-4 inch, 

 the total effect both ways being less than 3 inches. 



It is not surprising that it should be difficult to separate such 

 a small effect as this into a solar and lunar tide. 



Section IV. Diurnal Tide at Caherciveen. 

 In discussing the solar and lunar diurnal tides involved in 

 the tables calculated for Caherciveen, the following results were 

 arrived at : — 



I. Diurnal tide in, height at high water. 



1. Maximum value of lunar tidefor positive heights = 0-1 5 ft. 



2. Maximum value of lunar tide for negative heights = 0-20 ft. 



3. Maximum value of solar tide =0-245 ft. 



4. Diurnal solitidal interval =^^ 28"». 



5. Ageof lunar tide =5^4^. 



