AECTIC SEAS.— PAET IY. NOETHUMBEELAND SOUND. 
321 
determine the Lunar Diurnal Tide *. It so happened, during the observations, that the 
time of vanishing of the whole Diurnal Tide at Low Water corresponded very closely 
with the time of vanishing of the Moon’s declination. 
So that we have, at the same times, 
[jj= 0, D=0, 
which reduces the general expression at these times to 
S sin 2crcos(s— ^)=0. (3) 
The times corresponding to 
jM,=0, D=0 
were 
h m 
1st June 3 0 a.m. 
15th „ 4 30 p.m. 
28th „ 9 30 a.m. 
If we now take the hours of Low Water of the Tides occurring nearest to the time 
of the Moon’s declination vanishing, we find : — 
h m 
1st June s= 2 40 a.m. 
15th „ 1 10 p.m. 
28th „ 1 38 a.m. 
Mean value of s . 1 49 
Now from equation (3) we have 
hence 
and, finally, 
s-i,= 6 h or 18 h , 
l h 49 m — « s =6 h or 18 h ; 
?,= — 4 h 11“ 
orf +T h 49 m . 
The Diurnal Tide at High Water, when ^ = 0, is represented by 
D=S sin 2<r cos 
and had the following values : — 
1st June D= +0-234 ft. 
16th „ -0-360 „ 
28th „ +0-302 „ 
Mean value of D . . 0-299 „ 
* See Note A, p. 327. 
T An examination of the signs of the numerical values of the tide shows that the negative value of i s must 
he chosen. 
