4 On Cotidal lines of Diurnal and Semi-diurnal Tides 
the period during which the tidal observations were made, and 
the names of the observers 
A diagram (No. 1) shows these results graphically. A curved 
line corresponding to the general outline of the shore cutting off 
its irregularities, is drawn on the chart of the Gulf Coast, and 
then developed into a straight line. Thus the tidal stations are 
plotted at their distances from each other, measured along the 
general line of the coast. For use by navigators any interme- 
diate stations may be marked in, in the same wa , and a rough 
ny aoe tie to the channster rot the eae $e obtained by the 
interpolation 
The least observed height is 0°9 feet at Brazos Santiago, and 
the greatest 2°5 feet at Cedar Keys. The least height of the 
average semi-diurnal tide is 0°16 feet at South West | pass, and 
the greatest 2-40 feet at Cedar Keys. The least height of the 
average diurnal eg at 21 feet at Cape Florida, and the greatest 
1°80 feet at St. Mark’s. Of course these numbers are for rea- 
sons easily seen ni ip approximation 
As we enter the Gulf of Mexico by the Straits of Florida the 
height of the tide first increases, then decreases. Passing into 
the bight at the ge end of the Florida peninsula the rise is 
greatest. West of St. George’s it diminishes, to rise again in the 
bight formed by 8 Southern coast of Louisiana and the eastern 
coast of Texas 
In the decompositions here traced, and in the very laborious 
discussions tentative and final of the whole of the observations 
upon which this ‘pores is based, I would acknowledge the great 
assistance derived from the labors of Assissant L. F. Pourtales in 
charge of the tidal division of the Coast Survey. The unwearied 
assiduity of his own labors and his intelligent supervision of the 
work of others, has been felt at every step in the progress of 
oe investigations. They have required on his part great re- 
ources of ingenuity, patience and knowledge. 
In discussing semi-diurnal tides, the 1 lunitidal interval of high 
or low water varying only froma certain mean within moderate 
limits affords a cardinal datum (the establishment) for the times. 
In the diurnal tide this datum is wanting. The law of the change 
of the diurnal tide as expressed in the formula of Prof. Airy 
eee: coe ae Eneyc. Metrop., p. 254, Art. 46) is in general — 
but the ee flatness in the form of the curves at 
nee relations 0: moon’s right ascension and declina- 
tion, required by the aeetee does not occur, The general 
tidal intervals of high water. About the maximum of decli- — 
n for some four to ox days the lunitidal intervals are 
moderately cotta, and the average of these is what I me 
mae nama ae whet 
