AND ON THE DIURNAL INEQUALITY. 
25 
The Diurnal Inequality from Observations. 
46. I shall follow the same order of place which I have employed in stating the 
tide-hours. The amount of the diurnal inequality given is the greatest difference 
of the two successive tides. 
Falkland Isles. Port Louis. — An excellent series of observations by Sir James 
C. Ross, beginning May 10, 1 842. Nine semilunations complete ; and the dependence 
of the diurnal inequality on the moon’s declination throughout regular. 
High water heights : diurnal inequality = 2 ft. Difference of mean springs and 
neaps = 2 ft. 
Low water heights : diurnal inequality = 2 ft. Difference of mean springs and 
neaps = 2 ft. 
The age of the diurnal inequality is about a day and a half. 
Cape Horn. St. Martin's Cove. — Observations by Sir J. Ross. Three semiluna- 
tions, tolerably regular. Sir J. Ross himself remarks*, that the diurnal inequality-f' 
“ is as great here as at the Falkland Isles, and at first seemed to present most unac- 
countable irregularities ; but the limited period of observation did not admit of 
thorough investigation.” 
High water heights : diurnal inequality = 2 ft. Difference of mean springs and 
neaps = ft. 
Low water heights: diurnal inequality = l^ft. Difference of mean springs and 
neaps = 1 ^ ft. 
High water times. There is a large diurnal inequality in the lunitidal intervals, 
amounting sometimes to 2^ hours, while the semimensual inequality also appears 
to amount to two hours. 
The following results are derived from the new observations already quoted : — 
Callao. — ^No definite result. See before. 
Guayaquil. Puna Is. — Apparently diurnal inequality in high water heights. 
Panama. — No apparent diurnal inequality. 
Nicoya. — High water heights : diurnal inequality = 1 ft. Low water heights : 
diurnal inequality = ^ft. 
Realejo. — High water heights : diurnal inequality = 1 ft. Low water heights : 
diurnal inequality = \ ft. Apparently diurnal inequality in the high water and low 
water times, but irregular in the observations. 
Acapulco. — Apparently diurnal inequality, but small and doubtful. 
Magdalena Bay. — High water heights : diurnal inequality = 1 ft ; low water 
heights, not apparent. High water times : diurnal inequality = 2^ hours : but these 
results doubtful, from the shortness of the series and its irregularity. 
Columbia River. — Diurnal inequality not apparent. 
King George’s Sound. — High water heights : diurnal inequality = 1 f ft. 
* Voyage, ii. 313. 
t He says “ the semidiurnal inequality,” but it is plain that he means our diurnal inequality. 
MDCCCXLVIII. E 
