346 Prof. A. D. Bache on Tidal Observations. 
A solution of ilmenite in hydrochloric acid, effected at a gentle 
heat, contains the ordinary form of titanic acid, but that dissolved 
from sphene under similar cireumstanees, has the characters of 
the new modification. When the acid precipitated from this so- 
pose the sphene, the titanic acid is obtained in the ordinary form, 
and is converted into the new modification by diluting and boil- 
ing its solution. 
“his state of titanic acid corresponds perhaps to the soluble 
form of the metatitanic acid of Demoly, who has described under 
that name the insoluble form of titanic acid thrown down on 
boiling its sulphuric solution, and existing in salts as TisQs, cor-,. 
responding to an anhydrous monobasic acid. The real nature 
of this modified titanic acid, and the action of sulphuric acid in 
thus precipitating it from its solutions, are questions which I pro- 
se mine at the earliest opportunity. 
Montreal, C. E, July 4th, 1852, 
Arr. XXXIV.— Additional Notes of a Discussion of Tidal ott 
servations made in connection with the Coast Survey at Cat 
Island, Louisiana; by Prof. A. D. Bacwe, Superintendent 
U.S. Coast Survey.* 
In my communication on the subject of the tides at Cat Island, 
coast of Louisiana, at the New Haven meeting of the American 
Association,t I showed that I had succeeded in decomposing the 
curves of rise and fall into a diurnal and semidiurnal curve, which 
were nearly: curves of sines; the diurnal curve having its maxi- 
mum approximately nine hours in advance of the first maximum 
of the semidiurnal curve, and the interference of these two waves 
producing the tidal wave as observed. The comparison of the 
curves deduced from the observations for three months, and the 
computed curves of sines, was shown to be satisfactory. This 
comparison, made as before by averages of periods of a week 
combined into one general mean, has now been extended to the 
whole year, as shown in the subjoined table. By increasing the 
maximum ordinate of the diurnal curve 0:02 of a foot, whic 
will make the rise and fall agree more nearly with the average 
deduced from observation, we obtain, as shown in No. 2, a result- 
ing curve not differing in any ordinate more than a quarter of an 
inch from observation, and in which the positive and negative - 
errors nearly balance, and the mean error deduced by summing 
the square of the errors is little more than one-eighth of an inch. 
memset 
'* Read at the meeting of the American Association at Albany, and revised by. 
the author, for publication in the American Journal of Science. 
+ See this Jour., xii, 341. 
