26 Co-tidal lines of the Pacific Coast of the United States. 
cotidal line with the meridian N. 35° 30’ W. and the mean co- 
tidal hour 18> 50™, the difference of establishment for one geo- 
graphical mile perpendicular to the cotidal line 4:7 minutes. As 
the observations at Santa Cruz were comparatively few in num- 
ber, it may be more proper to leave out that station, which will 
give for the corresponding results to those just stated N. 36° 43/ 
W., for the angle of the cotidal line, 184 58™ for the mean cotidal 
hour, and 3-9 minutes for the cotidal difference in one geograph- 
ical mile. 
Omitting Bodega from this group we obtain for the cotidal “7 
gle N. 37° 26’ W., for the mean ese args 184 50™, and fo 
the change of hour in one mile 3-9 mit 
Omitting Bodega and San Prudence trot the first group, the 
three southern stations, San Luis Obispo, Monterey and Santa 
Cruz, give for the same values N. 33° 06’ W., 185 18™, and 4:9 
minutes. The direction of the cotidal line being nearly the 
same, its denomination only is changed. The 18} hours would 
give nearly 18% if carried to the cotidal line of the first hypoth- 
esis, 185 50™, which is a good agreement. 
Omissions at the other end of the group produce the same re- 
sult. Leaving out San Luis Obispo from 1, we obtain for the 
cotidal angle N. 36° 30’ W., cotidal hour 18" 47™, change per 
mile 4-4 minutes. The same result is obtained by other omis- 
sions in the series. . 
The introduelion of Humboldt into a group with Bodega and 
San Francisco gives results materially different from those ob- 
tained, reducing the cotidal angle to 18° 05’, and increasing the 
velocity to 40 miles per hour. : 
The combination of San Pedro with southern stations also 
changes the results so rapidly as to prove that the group is lim- 
ited to the south of Point Conception. 
The proof seems complete that these five stations form a sin- 
gle group. Using the determination in which Santa Cruz is 
omitted for reasons already stated, we have for the cotidal angle 
N. 36° 43’ W., which gives an inclination to the general line of 
the coast of diate ten degrees. The line of nineteen hours 
meets the coast north of Point Afio Nuevo, and between it and 
Point San Pedro. 
e comparison of the observed and computed establishments 
from either of these hypotheses, is very satisfactory, from that of — 
the five stations. Santa Cruz alone stands out with a difference 
greater than fifteen minutes. For the second list of four stations 
the greatest difference is twelve I and the mean without 
regard to signs is but six minutes. 
The velocity of the tide wave is less aniicieery from the 
other data rising to but fifteen miles per hour. ‘The de 7 
