348 Prof. A. D. Bache on Tidal Observations. 
irregular tides occur near the time of the moon’s passing the 
duced from a less number of observations than the others, and 
are therefore less reliable. The following table gives the average 
heights, with the number of days from which they have been 
educed. No advantage resulted from displacing the epoch of 
the moon’s declination relatively to the day of highest tide. 
TABLE No. IL (Diacram 2.) 
Showing the value of the maximum ordinates of the diurnal curve, on the several days 
from zero of declination of the moon to zero again, with the number of days from 
which the results are deduced. 
Days from zero! 
of declination, I | 2 34 :4)°5| 6) 9 8| 9| 10| 1 | 12 13| 14 
No. of observa-| 
tions, | eo 
i | EQ aay 
Heights. (0°33/0:33! 0-32! 0-41| 0-59) 0-65) 0-78) 0 87| 0-85) 0°77] 0-70] 0-58) 0°51 
Nat. sin. 2x : 
5 4 4 7-3 xy EQ Fad 4 Ks Ak In| O94) 
Ld + 
o. 2. 
for the diurnal inequality, namely, dh=C. sin 20’; in which dh is 
the difference in height of two consecutive high or low waters, 
of the moon. The following table contains the greatest heights _ 
of the diurnal curves during the several lunations of the year, 
with the values of the sun’s declination and of the moon’s dec- 
lination, grouped as described in the several columns. 
TABLE No. IIL (Dracram No. 3.) 
Showing the effect of change of sun’s declination on height. 
\Natural sine 2 sun’s declination. Bem’ phsong A csag san ek ey ~ diurnal curve. 
Greater than 70° eae ST 6 a en er ee 
70 to 60 6 ‘577 a 
60 to 40 6 “565 og 
40 to 20 | 5 530 094 
20 to 00 4 “550 074 
The effect of the change of parallax of the moon may be 
shown satisfactorily by grouping the values of the heights at the 
greatest southern declination of the moon, and for the greatest 
northern declination, for the year; comparing them for slightly 
varying declinations of the moon, for mean declinations of the 
sun, and for large variations of the parallax. The result is 
shown in the following table, and in Diagram No. 4. ee 
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