2 On Cotidal lines of Diurnal and Semi-diurnal Tides 
way of preparing for the present discussion and to avoid 
pani into too great length at this time, I gave at the last 
meeting a = Assuciation an account of the tidal observations 
r Gulf Coast, and showed the type curves for the 
ferent’ stitions from Cape Florida to the Rio Grande.* I also 
explained the method of decomposition of the curves of obser- 
ation into diurnal and and semi-diurnal waves, an gave the 
analysis of the type curves at the several tidal stations. From 
Cape Florida and along the keys, and up the western coast of the 
peninsula, to St. George’s, the tides are of the half day class with 
a large diurnal inequality; from St. George’s which belongs to 
the day class to South West Pass they are of the day type, the 
semi-diurnal tide almost disappearing; at Derniére Isle, Caleasieu 
and Galveston they resume as a rule the half day type, and lose 
it almost completely at Aransas and the mouth of the Rio Grande, 
The Derniére Isle and less distinctly, the Calcasieu tides show 
cases of interference in the semi-diurnal wave, two high waters 
being at times easily traced in the semi- diurnal curves. 
The character of the tidal phenomena themselves, the pecu- 
liarities in configuration and in depth of the basin, the limited 
extent over which our researches Spread, and various other cir- 
> ay aie contribute to render this work less satisfactory than 
the former. Some of these will in the end Saeco as the Gulf 
is more re fully explored in the progress of the survey. Our infor- 
mation thus far extends to but one entrance of the basin, that 
by the Gulf of Florida, and of this to but one asa while of 
the nature of the tide wave which enters from the Caribbean Sea 
through the Straits between the western end of Cubs and the 
eastern end of Yucatan, we have no reliable information. Some 
of these causes render general speculation premature, and lie at 
the very threshold of attempts 7 trace out the great interference 
problems which present themse 
The progress of this ductaeaes has also shown that observa- 
tions of longer period are necessary in many cases to give data 
for conclusive results. 
This of itself is a great point gained and the practical results 
for the charts of this coast have themselves repaid all the labor 
whi een expended on the observation. Navigators vee - 
absolutely without information other than the most vague in 
regard to the tides of the Gulf. 
The hourly observations at each station being plotted in dia- a 
grams upon a suitable scale, the curves of observation Were = 
decomposed by the graphical method introduced by Mr. Pour- 
tales, into a diurnal and semi-diumal curve. It may be proper : 
to observe here that several comparisons have been made between 
this method and that which I had formerly used by the sine 
* Proceedings Amer. Assoc, A a 
Jour, Sci, and ee Jan. 1856, p. Pe Providence meeting, 1855, p. 152, and Am. 
