SUBMERGENCE AND EXPOSURE ino 
of actual mean tides at the former station were found to resemble those for the 
same tides at the latter station.* 
If, then, we allow for the 0.4 foot greater height of high water at Cold Spring 
Harbor, we can, from this predicted curve for Willet’s Point, determine with 
sufficient accuracy the probable duration of submergence and of exposure of any 
level between tide-marks at Cold Spring Harbor. That is, we can determine 
by measurement, between the points of intersection of the horizontal line 
representing any level with the curve, the submergence and exposure of that 
level per lunar day per month, and so the total for the whole season of six 
months. 
Table A, page 135, gives the duration of submergence and emergence, per 
lunar day and per average calendar month, for various levels from —1.25 feet 
to +9.00 feet measured from this predicted curve. This table shows in the 
second and third columns the average total submergence in hours per month of 
each level. The emergence of levels below mean low water and the submergence 
N00 RC SO 
 - ON Ae ee 
a a a 
ee Na 
INEM TR Gs RG A Pe Se 
mmm tL 
Oe a EE a SC a 2 Ve 
EET SS 7 Fe TE 
0 
Time IZPM. 1AM. 24M. 3AM. 4AM. SAM. 6AM. 7A.M. BA.M. 9AM, IOA.M, A.M. 12M. 12M. 2PM. 32M. 4PM. SPM. 6PM. 72M. SPM. OPM. IORM, HRM, 122M. 



Fic. 4.—Chart of tidal-curve of two successive mean tides, recorded at Willet’s 
Point, New York, on July 18, 1894 (supplied by the U. S. Coast and Geodetic Survey). 
(In comparing this curve with that in plate XIV note that the horizontal unit of the 
scale, representing an hour of time, is 20 per cent greater than the vertical unit, 
representing a foot in height, instead of equal to it, as in plate XIV. This accounts 
in part for the greater flattening of the crest and hollow of the curve.) 
of levels above 6.5 feet was measured on the predicted curve for Willet’s Point 
for all tides of the season. In determining the submergence and exposure of 
levels from 5 feet upward, allowance was made for the greater height of high 
water at Cold Spring Harbor, by measuring the submergence for each level at 
0.4 feet lower down from the crest of the curve of the tide for that day, or by 
measuring it on the curve of a tide of proper height, though it happened to be 
on another day. The durations so obtained when divided by 6 give the average 
durations of submergence or emergence for each month of the growing season. 
The submergence of the lower levels was obtained by subtracting the total 
* Actual records of the tides of the Inner Harbor at Cold Spring Harbor were made 
with a tide-gage loaned by the U. S. Coast and Geodetic Survey, in July, August, and 
September, 1913. The form of this curve corresponds very closely with the con- 
structed curve shown in plate v1 and with the predicted tide-curve for Willet’s Point. 
The most striking peculiarity of the curve recorded at Cold Spring Harbor in 1913 
is the sharpness of the trough at low water. This probably means that the times of 
“ihe given on page 136, for plants growing near mean low water are slightly 
too large. 
