Prof. A. D. Bache on Tidal Observations. 357 wd, 
2. Semidiurnal Curve. 
The results in relation to the semidiurnal curve have exceeded 
my anticipations. ‘The half-monthly inequality, both in height 
and time, is very well shown by the maximum ordinates deduced ; 
though the greatest value of the height is only 0-22 feet, and the 
Poialarition in the separate observed high waters fall upon hours 
instead of minutes. In the following table, the maximum ordin- 
ates obtained by the method of groups are used, and the small 
correction for the difference between maximum ‘and high water 
ordinates is omitted. The latter contains time of moon’s transit 
corresponding to observed height; and the height computed from 
the formula given by Mr. Lubbock as resulting from Bernouilli’s 
theory, and the difference between observation and theory. 
TABLE No. XVL 
Showing half-monthly inequality in height. 
Pe ce, o—G. 
oe S| Observed height. | Computed height. gre ef stag 
05 "990-4. 223 _— oe 
13 i -206 — ‘ol 
24 o "174 “025 
33 "147 "131 o16 
t 4g “132 087 045 
ages ae oe = 
=i : ‘047 "0 - 
73 "074 “087 gress 
83 ay “131 —o18 
93 “435 174 —*o3 
rod 133 -206 —*O7 
114 189 +223 — *034 
The greatest difference between observed and computed heights 
is 0-073, and the least difference 0-003; and the mean, without 
regard to sine, is 0-026. Diagram No. 8 shows the observed and 
computed curves of half-moutbly inequality of” heights. The 
average interval corresponds t 35m of the moon’s transit ; 
Which is therefore the zero point, or epoch of the half-monthly 
inequality in the interv. 
The interval wieieadne to the moon’s - “at 
transit at 3 30 is 11 45 
for 9 30 “ 13 05 
Diff is 1 20 
which, converted into are, is 20° 
Log tan 20° = log (ae 956107; 
1 
wince is nearly sins same as be obtained by in ae for Liv- 
“rime Vol. XIV, No, 42.—Noy., 1852. 
